diff options
| author | Andreas Jaeger <aj@suse.de> | 2012-05-03 09:46:57 +0200 |
|---|---|---|
| committer | Andreas Jaeger <aj@suse.de> | 2012-05-03 09:46:57 +0200 |
| commit | 7ac30cc5f0460b72646abffee96584e063f96b5a (patch) | |
| tree | a355588263e608d007b06a98e5588897b70a02f9 | |
| parent | e2dbf201abdfa13fc4035a1a8888ecec91bef44c (diff) | |
| download | glibc-7ac30cc5f0460b72646abffee96584e063f96b5a.zip glibc-7ac30cc5f0460b72646abffee96584e063f96b5a.tar.gz glibc-7ac30cc5f0460b72646abffee96584e063f96b5a.tar.bz2 | |
Move FAQ to wiki
The FAQ is now at http://sourceware.org/glibc/wiki/FAQ and not
anymore part of the repository.
| -rw-r--r-- | ChangeLog | 10 | ||||
| -rw-r--r-- | FAQ | 1976 | ||||
| -rw-r--r-- | FAQ.in | 1701 | ||||
| -rw-r--r-- | Makefile | 4 | ||||
| -rw-r--r-- | manual/install.texi | 8 | ||||
| -rwxr-xr-x | scripts/gen-FAQ.pl | 144 |
6 files changed, 15 insertions, 3828 deletions
@@ -1,3 +1,13 @@ +2012-05-03 Andreas Jaeger <aj@suse.de> + + * FAQ: Removed. + * FAQ.in: Likewise. + * scripts/gen-FAQ.pl: Likewise. + * manual/install.texi (Installation): Point to online location of + FAQ. + * Makefile (files-for-dist): Remove FAQ. + (FAQ): Remove. + 2012-05-02 Allan McRae <allan@archlinux.org> * elf/Makefile: (LDFLAGS-nodel2mod3.so: Use $(no-as-needed). @@ -1,1976 +0,0 @@ - Frequently Asked Questions about the GNU C Library - -This document tries to answer questions a user might have when installing -and using glibc. Please make sure you read this before sending questions or -bug reports to the maintainers. - -The GNU C library is very complex. The installation process has not been -completely automated; there are too many variables. You can do substantial -damage to your system by installing the library incorrectly. Make sure you -understand what you are undertaking before you begin. - -If you have any questions you think should be answered in this document, -please let me know. - - --drepper@redhat.com - -~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ - -1. Compiling glibc - -1.1. What systems does the GNU C Library run on? -1.2. What compiler do I need to build GNU libc? -1.3. When I try to compile glibc I get only error messages. - What's wrong? -1.4. Do I need a special linker or assembler? -1.5. Which compiler should I use for powerpc? -1.6. Which tools should I use for ARM? -1.7. Do I need some more things to compile the GNU C Library? -1.8. What version of the Linux kernel headers should be used? -1.9. The compiler hangs while building iconvdata modules. What's - wrong? -1.10. When I run `nm -u libc.so' on the produced library I still - find unresolved symbols. Can this be ok? -1.11. What are these `add-ons'? -1.12. My XXX kernel emulates a floating-point coprocessor for me. - Should I enable --with-fp? -1.13. When compiling GNU libc I get lots of errors saying functions - in glibc are duplicated in libgcc. -1.14. Why do I get messages about missing thread functions when I use - librt? I don't even use threads. -1.15. What's the problem with configure --enable-omitfp? -1.16. I get failures during `make check'. What should I do? -1.17. What is symbol versioning good for? Do I need it? -1.18. How can I compile on my fast ix86 machine a working libc for my slow - i386? After installing libc, programs abort with "Illegal - Instruction". -1.19. `make' complains about a missing dlfcn/libdl.so when building - malloc/libmemprof.so. How can I fix this? -1.20. Which tools should I use for MIPS? -1.21. Which compiler should I use for powerpc64? -1.22. `make' fails when running rpcgen the first time, - what is going on? How do I fix this? -1.23. Why do I get: - `#error "glibc cannot be compiled without optimization"', - when trying to compile GNU libc with GNU CC? - -2. Installation and configuration issues - -2.1. Can I replace the libc on my Linux system with GNU libc? -2.2. How do I configure GNU libc so that the essential libraries - like libc.so go into /lib and the other into /usr/lib? -2.3. How should I avoid damaging my system when I install GNU libc? -2.4. Do I need to use GNU CC to compile programs that will use the - GNU C Library? -2.5. When linking with the new libc I get unresolved symbols - `crypt' and `setkey'. Why aren't these functions in the - libc anymore? -2.6. When I use GNU libc on my Linux system by linking against - the libc.so which comes with glibc all I get is a core dump. -2.7. Looking through the shared libc file I haven't found the - functions `stat', `lstat', `fstat', and `mknod' and while - linking on my Linux system I get error messages. How is - this supposed to work? -2.8. When I run an executable on one system which I compiled on - another, I get dynamic linker errors. Both systems have the same - version of glibc installed. What's wrong? -2.9. How can I compile gcc 2.7.2.1 from the gcc source code using - glibc 2.x? -2.10. The `gencat' utility cannot process the catalog sources which - were used on my Linux libc5 based system. Why? -2.11. Programs using libc have their messages translated, but other - behavior is not localized (e.g. collating order); why? -2.12. I have set up /etc/nis.conf, and the Linux libc 5 with NYS - works great. But the glibc NIS+ doesn't seem to work. -2.13. I have killed ypbind to stop using NIS, but glibc - continues using NIS. -2.14. Under Linux/Alpha, I always get "do_ypcall: clnt_call: - RPC: Unable to receive; errno = Connection refused" when using NIS. -2.15. After installing glibc name resolving doesn't work properly. -2.16. How do I create the databases for NSS? -2.17. I have /usr/include/net and /usr/include/scsi as symlinks - into my Linux source tree. Is that wrong? -2.18. Programs like `logname', `top', `uptime' `users', `w' and - `who', show incorrect information about the (number of) - users on my system. Why? -2.19. After upgrading to glibc 2.1 with symbol versioning I get - errors about undefined symbols. What went wrong? -2.20. When I start the program XXX after upgrading the library - I get - XXX: Symbol `_sys_errlist' has different size in shared - object, consider re-linking - Why? What should I do? -2.21. What do I need for C++ development? -2.22. Even statically linked programs need some shared libraries - which is not acceptable for me. What can I do? -2.23. I just upgraded my Linux system to glibc and now I get - errors whenever I try to link any program. -2.24. When I use nscd the machine freezes. -2.25. I need lots of open files. What do I have to do? -2.26. How do I get the same behavior on parsing /etc/passwd and - /etc/group as I have with libc5 ? -2.27. What needs to be recompiled when upgrading from glibc 2.0 to glibc - 2.1? -2.28. Why is extracting files via tar so slow? -2.29. Compiling programs I get parse errors in libio.h (e.g. "parse error - before `_IO_seekoff'"). How should I fix this? -2.30. After upgrading to glibc 2.1, libraries that were compiled against - glibc 2.0.x don't work anymore. -2.31. What happened to the Berkeley DB libraries? Can I still use db - in /etc/nsswitch.conf? -2.32. What has do be done when upgrading to glibc 2.2? -2.33. The makefiles want to do a CVS commit. -2.34. When compiling C++ programs, I get a compilation error in streambuf.h. -2.35. When recompiling GCC, I get compilation errors in libio. -2.36. Why shall glibc never get installed on GNU/Linux systems in -/usr/local? -2.37. When recompiling GCC, I get compilation errors in libstdc++. - -3. Source and binary incompatibilities, and what to do about them - -3.1. I expect GNU libc to be 100% source code compatible with - the old Linux based GNU libc. Why isn't it like this? -3.2. Why does getlogin() always return NULL on my Linux box? -3.3. Where are the DST_* constants found in <sys/time.h> on many - systems? -3.4. The prototypes for `connect', `accept', `getsockopt', - `setsockopt', `getsockname', `getpeername', `send', - `sendto', and `recvfrom' are different in GNU libc from - any other system I saw. This is a bug, isn't it? -3.5. On Linux I've got problems with the declarations in Linux - kernel headers. -3.6. I don't include any kernel headers myself but the compiler - still complains about redeclarations of types in the kernel - headers. -3.7. Why don't signals interrupt system calls anymore? -3.8. I've got errors compiling code that uses certain string - functions. Why? -3.9. I get compiler messages "Initializer element not constant" with - stdin/stdout/stderr. Why? -3.10. I can't compile with gcc -traditional (or - -traditional-cpp). Why? -3.11. I get some errors with `gcc -ansi'. Isn't glibc ANSI compatible? -3.12. I can't access some functions anymore. nm shows that they do - exist but linking fails nevertheless. -3.13. When using the db-2 library which comes with glibc is used in - the Perl db modules the testsuite is not passed. This did not - happen with db-1, gdbm, or ndbm. -3.14. The pow() inline function I get when including <math.h> is broken. - I get segmentation faults when I run the program. -3.15. The sys/sem.h file lacks the definition of `union semun'. -3.16. Why has <netinet/ip_fw.h> disappeared? -3.17. I get floods of warnings when I use -Wconversion and include - <string.h> or <math.h>. -3.18. After upgrading to glibc 2.1, I receive errors about - unresolved symbols, like `_dl_initial_searchlist' and can not - execute any binaries. What went wrong? -3.19. bonnie reports that char i/o with glibc 2 is much slower than with - libc5. What can be done? -3.20. Programs compiled with glibc 2.1 can't read db files made with glibc - 2.0. What has changed that programs like rpm break? -3.21. Autoconf's AC_CHECK_FUNC macro reports that a function exists, but - when I try to use it, it always returns -1 and sets errno to ENOSYS. -3.22. My program segfaults when I call fclose() on the FILE* returned - from setmntent(). Is this a glibc bug? -3.23. I get "undefined reference to `atexit'" - -4. Miscellaneous - -4.1. After I changed configure.in I get `Autoconf version X.Y. - or higher is required for this script'. What can I do? -4.2. When I try to compile code which uses IPv6 headers and - definitions on my Linux 2.x.y system I am in trouble. - Nothing seems to work. -4.3. When I set the timezone by setting the TZ environment variable - to EST5EDT things go wrong since glibc computes the wrong time - from this information. -4.4. What other sources of documentation about glibc are available? -4.5. The timezone string for Sydney/Australia is wrong since even when - daylight saving time is in effect the timezone string is EST. -4.6. I've build make 3.77 against glibc 2.1 and now make gets - segmentation faults. -4.7. Why do so many programs using math functions fail on my AlphaStation? -4.8. The conversion table for character set XX does not match with -what I expect. -4.9. How can I find out which version of glibc I am using in the moment? -4.10. Context switching with setcontext() does not work from within - signal handlers. - - -~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ - -1. Compiling glibc - -1.1. What systems does the GNU C Library run on? - -{UD} This is difficult to answer. The file `README' lists the architectures -GNU libc was known to run on *at some time*. This does not mean that it -still can be compiled and run on them now. - -The systems glibc is known to work on as of this release, and most probably -in the future, are: - - *-*-gnu GNU Hurd - i[3456]86-*-linux-gnu Linux-2.x on Intel - m68k-*-linux-gnu Linux-2.x on Motorola 680x0 - alpha*-*-linux-gnu Linux-2.x on DEC Alpha - powerpc-*-linux-gnu Linux and MkLinux on PowerPC systems - powerpc64-*-linux-gnu Linux-2.4+ on 64-bit PowerPC systems - sparc-*-linux-gnu Linux-2.x on SPARC - sparc64-*-linux-gnu Linux-2.x on UltraSPARC - arm-*-none ARM standalone systems - arm-*-linux Linux-2.x on ARM - arm-*-linuxaout Linux-2.x on ARM using a.out binaries - mips*-*-linux-gnu Linux-2.x on MIPS - ia64-*-linux-gnu Linux-2.x on ia64 - s390-*-linux-gnu Linux-2.x on IBM S/390 - s390x-*-linux-gnu Linux-2.x on IBM S/390 64-bit - cris-*-linux-gnu Linux-2.4+ on CRIS - -Ports to other Linux platforms are in development, and may in fact work -already, but no one has sent us success reports for them. Currently no -ports to other operating systems are underway, although a few people have -expressed interest. - -If you have a system not listed above (or in the `README' file) and you are -really interested in porting it, see the GNU C Library web pages to learn -how to start contributing: - - http://www.gnu.org/software/libc/resources.html - - -1.2. What compiler do I need to build GNU libc? - -{UD} You must use GNU CC to compile GNU libc. A lot of extensions of GNU CC -are used to increase portability and speed. - -GNU CC is found, like all other GNU packages, on - - ftp://ftp.gnu.org/pub/gnu - -and the many mirror sites. ftp.gnu.org is always overloaded, so try to find -a local mirror first. - -You should always try to use the latest official release. Older versions -may not have all the features GNU libc requires. The current releases of -gcc (3.2 or newer) should work with the GNU C library (for MIPS see question 1.20). - -Please note that gcc 2.95 and 2.95.x cannot compile glibc on Alpha due to -problems in the complex float support. - - -1.3. When I try to compile glibc I get only error messages. - What's wrong? - -{UD} You definitely need GNU make to build GNU libc. No other make -program has the needed functionality. - -We recommend version GNU make version 3.79 or newer. Older versions have -bugs and/or are missing features. - - -1.4. Do I need a special linker or assembler? - -{ZW} If you want a shared library, you need a linker and assembler that -understand all the features of ELF, including weak and versioned symbols. -The static library can be compiled with less featureful tools, but lacks key -features such as NSS. - -For Linux or Hurd, you want binutils 2.13 or higher. These are the only -versions we've tested and found reliable. Other versions may work but we -don't recommend them, especially not when C++ is involved. - -Other operating systems may come with system tools that have all the -necessary features, but this is moot because glibc hasn't been ported to -them. - - -1.5. Which compiler should I use for powerpc? - -{} Removed. Does not apply anymore. - - -1.6. Which tools should I use for ARM? - -{} Removed. Does not apply anymore. - - -1.7. Do I need some more things to compile the GNU C Library? - -{UD} Yes, there are some more :-). - -* GNU gettext. This package contains the tools needed to construct - `message catalog' files containing translated versions of system - messages. See ftp://ftp.gnu.org/pub/gnu or better any mirror - site. (We distribute compiled message catalogs, but they may not be - updated in patches.) - -* Some files are built with special tools. E.g., files ending in .gperf - need a `gperf' program. The GNU version (now available in a separate - package, formerly only as part of libg++) is known to work while some - vendor versions do not. - - You should not need these tools unless you change the source files. - -* Perl 5 is needed if you wish to test an installation of GNU libc - as the primary C library. - -* When compiling for Linux, the header files of the Linux kernel must - be available to the compiler as <linux/*.h> and <asm/*.h>. - -* lots of disk space (~400MB for i?86-linux; more for RISC platforms). - -* plenty of time. Compiling just the shared and static libraries for - 35mins on a 2xPIII@550Mhz w/ 512MB RAM. On a 2xUltraSPARC-II@360Mhz - w/ 1GB RAM it takes about 14 minutes. Multiply this by 1.5 or 2.0 - if you build profiling and/or the highly optimized version as well. - For Hurd systems times are much higher. - - You should avoid compiling in a NFS mounted filesystem. This is - very slow. - - James Troup <J.J.Troup@comp.brad.ac.uk> reports a compile time for - an earlier (and smaller!) version of glibc of 45h34m for a full build - (shared, static, and profiled) on Atari Falcon (Motorola 68030 @ 16 Mhz, - 14 Mb memory) and Jan Barte <yann@plato.uni-paderborn.de> reports - 22h48m on Atari TT030 (Motorola 68030 @ 32 Mhz, 34 Mb memory) - - A full build of the PowerPC library took 1h on a PowerPC 750@400Mhz w/ - 64MB of RAM, and about 9h on a 601@60Mhz w/ 72Mb. - - -1.8. What version of the Linux kernel headers should be used? - -{AJ,UD} The headers from the most recent Linux kernel should be used. The -headers used while compiling the GNU C library and the kernel binary used -when using the library do not need to match. The GNU C library runs without -problems on kernels that are older than the kernel headers used. The other -way round (compiling the GNU C library with old kernel headers and running -on a recent kernel) does not necessarily work. For example you can't use -new kernel features if you used old kernel headers to compile the GNU C -library. - -{ZW} Even if you are using a 2.0 kernel on your machine, we recommend you -compile GNU libc with 2.2 kernel headers. That way you won't have to -recompile libc if you ever upgrade to kernel 2.2. To tell libc which -headers to use, give configure the --with-headers switch -(e.g. --with-headers=/usr/src/linux-2.2.0/include). - -Note that you must configure the 2.2 kernel if you do this, otherwise libc -will be unable to find <linux/version.h>. Just change the current directory -to the root of the 2.2 tree and do `make include/linux/version.h'. - - -1.9. The compiler hangs while building iconvdata modules. What's - wrong? - -{} Removed. Does not apply anymore. - - -1.10. When I run `nm -u libc.so' on the produced library I still - find unresolved symbols. Can this be ok? - -{UD} Yes, this is ok. There can be several kinds of unresolved symbols: - -* magic symbols automatically generated by the linker. These have names - like __start_* and __stop_* - -* symbols starting with _dl_* come from the dynamic linker - -* weak symbols, which need not be resolved at all (fabs for example) - -Generally, you should make sure you find a real program which produces -errors while linking before deciding there is a problem. - - -1.11. What are these `add-ons'? - -{UD} To avoid complications with export rules or external source code some -optional parts of the libc are distributed as separate packages, e.g., the -linuxthreads package. - -To use these packages as part of GNU libc, just unpack the tarfiles in the -libc source directory and tell the configuration script about them using the ---enable-add-ons option. If you give just --enable-add-ons configure tries -to find all the add-on packages in your source tree. This may not work. If -it doesn't, or if you want to select only a subset of the add-ons, give a -comma-separated list of the add-ons to enable: - - configure --enable-add-ons=linuxthreads - -for example. - -Add-ons can add features (including entirely new shared libraries), override -files, provide support for additional architectures, and just about anything -else. The existing makefiles do most of the work; only some few stub rules -must be written to get everything running. - -Most add-ons are tightly coupled to a specific GNU libc version. Please -check that the add-ons work with the GNU libc. For example the linuxthreads -add-on has the same numbering scheme as the libc and will in general only -work with the corresponding libc. - -{AJ} With glibc 2.2 the crypt add-on and with glibc 2.1 the localedata -add-on have been integrated into the normal glibc distribution, crypt and -localedata are therefore not anymore add-ons. - - -1.12. My XXX kernel emulates a floating-point coprocessor for me. - Should I enable --with-fp? - -{ZW} An emulated FPU is just as good as a real one, as far as the C library -is concerned. You only need to say --without-fp if your machine has no way -to execute floating-point instructions. - -People who are interested in squeezing the last drop of performance -out of their machine may wish to avoid the trap overhead, but this is -far more trouble than it's worth: you then have to compile -*everything* this way, including the compiler's internal libraries -(libgcc.a for GNU C), because the calling conventions change. - - -1.13. When compiling GNU libc I get lots of errors saying functions - in glibc are duplicated in libgcc. - -{EY} This is *exactly* the same problem that I was having. The problem was -due to the fact that configure didn't correctly detect that the linker flag ---no-whole-archive was supported in my linker. In my case it was because I -had run ./configure with bogus CFLAGS, and the test failed. - -One thing that is particularly annoying about this problem is that once this -is misdetected, running configure again won't fix it unless you first delete -config.cache. - -{UD} Starting with glibc-2.0.3 there should be a better test to avoid some -problems of this kind. The setting of CFLAGS is checked at the very -beginning and if it is not usable `configure' will bark. - - -1.14. Why do I get messages about missing thread functions when I use - librt? I don't even use threads. - -{UD} In this case you probably mixed up your installation. librt uses -threads internally and has implicit references to the thread library. -Normally these references are satisfied automatically but if the thread -library is not in the expected place you must tell the linker where it is. -When using GNU ld it works like this: - - gcc -o foo foo.c -Wl,-rpath-link=/some/other/dir -lrt - -The `/some/other/dir' should contain the thread library. `ld' will use the -given path to find the implicitly referenced library while not disturbing -any other link path. - - -1.15. What's the problem with configure --enable-omitfp? - -{} Removed. Does not apply anymore. - - -1.16. I get failures during `make check'. What should I do? - -{AJ} The testsuite should compile and run cleanly on your system; every -failure should be looked into. Depending on the failures, you probably -should not install the library at all. - -You should consider reporting it in bugzilla -<http://sourceware.org/bugzilla/> providing as much detail as possible. -If you run a test directly, please remember to set up the environment -correctly. You want to test the compiled library - and not your installed -one. The best way is to copy the exact command line which failed and run -the test from the subdirectory for this test in the sources. - -There are some failures which are not directly related to the GNU libc: -- Some compilers produce buggy code. No compiler gets single precision - complex numbers correct on Alpha. Otherwise, gcc-3.2 should be ok. -- The kernel might have bugs. For example on Linux/Alpha 2.0.34 the - floating point handling has quite a number of bugs and therefore most of - the test cases in the math subdirectory will fail. Linux 2.2 has - fixes for the floating point support on Alpha. The Linux/SPARC kernel has - also some bugs in the FPU emulation code (as of Linux 2.2.0). -- Other tools might have problems. For example bash 2.03 gives a - segmentation fault running the tst-rpmatch.sh test script. - - -1.17. What is symbol versioning good for? Do I need it? - -{AJ} Symbol versioning solves problems that are related to interface -changes. One version of an interface might have been introduced in a -previous version of the GNU C library but the interface or the semantics of -the function has been changed in the meantime. For binary compatibility -with the old library, a newer library needs to still have the old interface -for old programs. On the other hand, new programs should use the new -interface. Symbol versioning is the solution for this problem. The GNU -libc version 2.1 uses symbol versioning by default if the installed binutils -supports it. - -We don't advise building without symbol versioning, since you lose binary -compatibility - forever! The binary compatibility you lose is not only -against the previous version of the GNU libc (version 2.0) but also against -all future versions. - - -1.18. How can I compile on my fast ix86 machine a working libc for my slow - i386? After installing libc, programs abort with "Illegal - Instruction". - -{AJ} glibc and gcc might generate some instructions on your machine that -aren't available on i386. You've got to tell glibc that you're configuring -for i386 with adding i386 as your machine, for example: - - ../configure --prefix=/usr i386-pc-linux-gnu - -And you need to tell gcc to only generate i386 code, just add `-mcpu=i386' -(just -m386 doesn't work) to your CFLAGS. - -{UD} This applies not only to the i386. Compiling on a i686 for any older -model will also fail if the above methods are not used. - - -1.19. `make' complains about a missing dlfcn/libdl.so when building - malloc/libmemprof.so. How can I fix this? - -{AJ} Older make version (<= 3.78.90) have a bug which was hidden by a bug in -glibc (<= 2.1.2). You need to upgrade make to a newer or fixed version. - -After upgrading make, you should remove the file sysd-sorted in your build -directory. The problem is that the broken make creates a wrong order for -one list in that file. The list has to be recreated with the new make - -which happens if you remove the file. - -You might encounter this bug also in other situations where make scans -directories. I strongly advise to upgrade your make version to 3.79 or -newer. - - -1.20. Which tools should I use for MIPS? - -{AJ} You should use the current development version of gcc 3.2 or newer from -CVS. - -You need also recent binutils, anything before and including 2.11 will not -work correctly. Either try the Linux binutils 2.11.90.0.5 from HJ Lu or the -current development version of binutils from CVS. - -Please note that `make check' might fail for a number of the math tests -because of problems of the FPU emulation in the Linux kernel (the MIPS FPU -doesn't handle all cases and needs help from the kernel). - - -1.21. Which compiler should I use for powerpc64? - -{SM} You want to use at least gcc 3.2 (together with the right versions -of all the other tools, of course). - - -1.22. `make' fails when running rpcgen the first time, - what is going on? How do I fix this? - -{CO} The first invocation of rpcgen is also the first use of the recently -compiled dynamic loader. If there is any problem with the dynamic loader -it will more than likely fail to run rpcgen properly. This could be due to -any number of problems. - -The only real solution is to debug the loader and determine the problem -yourself. Please remember that for each architecture there may be various -patches required to get glibc HEAD into a runnable state. The best course -of action is to determine if you have all the required patches. - - -1.23. Why do I get: - `#error "glibc cannot be compiled without optimization"', - when trying to compile GNU libc with GNU CC? - -{AJ,CO} There are a couple of reasons why the GNU C library will not work -correctly if it is not complied with optimzation. - -In the early startup of the dynamic loader (_dl_start), before -relocation of the PLT, you cannot make function calls. You must inline -the functions you will use during early startup, or call compiler -builtins (__builtin_*). - -Without optimizations enabled GNU CC will not inline functions. The -early startup of the dynamic loader will make function calls via an -unrelocated PLT and crash. - -Without auditing the dynamic linker code it would be difficult to remove -this requirement. - -Another reason is that nested functions must be inlined in many cases to -avoid executable stacks. - -In practice there is no reason to compile without optimizations, therefore -we require that GNU libc be compiled with optimizations enabled. - - -. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - -2. Installation and configuration issues - -2.1. Can I replace the libc on my Linux system with GNU libc? - -{UD} You cannot replace any existing libc for Linux with GNU libc. It is -binary incompatible and therefore has a different major version. You can, -however, install it alongside your existing libc. - -For Linux there are three major libc versions: - libc-4 a.out libc - libc-5 original ELF libc - libc-6 GNU libc - -You can have any combination of these three installed. For more information -consult documentation for shared library handling. The Makefiles of GNU -libc will automatically generate the needed symbolic links which the linker -will use. - - -2.2. How do I configure GNU libc so that the essential libraries - like libc.so go into /lib and the other into /usr/lib? - -{UD,AJ} Like all other GNU packages GNU libc is designed to use a base -directory and install all files relative to this. The default is -/usr/local, because this is safe (it will not damage the system if installed -there). If you wish to install GNU libc as the primary C library on your -system, set the base directory to /usr (i.e. run configure --prefix=/usr -<other_options>). Note that this can damage your system; see question 2.3 for -details. - -Some systems like Linux have a filesystem standard which makes a difference -between essential libraries and others. Essential libraries are placed in -/lib because this directory is required to be located on the same disk -partition as /. The /usr subtree might be found on another -partition/disk. If you configure for Linux with --prefix=/usr, then this -will be done automatically. - -To install the essential libraries which come with GNU libc in /lib on -systems other than Linux one must explicitly request it. Autoconf has no -option for this so you have to use a `configparms' file (see the `INSTALL' -file for details). It should contain: - -slibdir=/lib -sysconfdir=/etc - -The first line specifies the directory for the essential libraries, the -second line the directory for system configuration files. - - -2.3. How should I avoid damaging my system when I install GNU libc? - -{ZW} If you wish to be cautious, do not configure with --prefix=/usr. If -you don't specify a prefix, glibc will be installed in /usr/local, where it -will probably not break anything. (If you wish to be certain, set the -prefix to something like /usr/local/glibc2 which is not used for anything.) - -The dangers when installing glibc in /usr are twofold: - -* glibc will overwrite the headers in /usr/include. Other C libraries - install a different but overlapping set of headers there, so the effect - will probably be that you can't compile anything. You need to rename - /usr/include out of the way before running `make install'. (Do not throw - it away; you will then lose the ability to compile programs against your - old libc.) - -* None of your old libraries, static or shared, can be used with a - different C library major version. For shared libraries this is not a - problem, because the filenames are different and the dynamic linker - will enforce the restriction. But static libraries have no version - information. You have to evacuate all the static libraries in - /usr/lib to a safe location. - -The situation is rather similar to the move from a.out to ELF which -long-time Linux users will remember. - - -2.4. Do I need to use GNU CC to compile programs that will use the - GNU C Library? - -{ZW} In theory, no; the linker does not care, and the headers are supposed -to check for GNU CC before using its extensions to the C language. - -However, there are currently no ports of glibc to systems where another -compiler is the default, so no one has tested the headers extensively -against another compiler. You may therefore encounter difficulties. If you -do, please report them as bugs. - -Also, in several places GNU extensions provide large benefits in code -quality. For example, the library has hand-optimized, inline assembly -versions of some string functions. These can only be used with GCC. See -question 3.8 for details. - - -2.5. When linking with the new libc I get unresolved symbols - `crypt' and `setkey'. Why aren't these functions in the - libc anymore? - -{} Removed. Does not apply anymore. - - -2.6. When I use GNU libc on my Linux system by linking against - the libc.so which comes with glibc all I get is a core dump. - -{UD} On Linux, gcc sets the dynamic linker to /lib/ld-linux.so.1 unless the -user specifies a --dynamic-linker argument. This is the name of the libc5 -dynamic linker, which does not work with glibc. - -For casual use of GNU libc you can just specify to the linker - --dynamic-linker=/lib/ld-linux.so.2 - -which is the glibc dynamic linker, on Linux systems. On other systems the -name is /lib/ld.so.1. When linking via gcc, you've got to add - -Wl,--dynamic-linker=/lib/ld-linux.so.2 - -to the gcc command line. - -To change your environment to use GNU libc for compiling you need to change -the `specs' file of your gcc. This file is normally found at - - /usr/lib/gcc-lib/<arch>/<version>/specs - -In this file you have to change a few things: - -- change `ld-linux.so.1' to `ld-linux.so.2' - -- remove all expression `%{...:-lgmon}'; there is no libgmon in glibc - -- fix a minor bug by changing %{pipe:-} to %| - -Here is what the gcc-2.7.2 specs file should look like when GNU libc is -installed at /usr: - ------------------------------------------------------------------------ -*asm: -%{V} %{v:%{!V:-V}} %{Qy:} %{!Qn:-Qy} %{n} %{T} %{Ym,*} %{Yd,*} %{Wa,*:%*} - -*asm_final: -%| - -*cpp: -%{fPIC:-D__PIC__ -D__pic__} %{fpic:-D__PIC__ -D__pic__} %{!m386:-D__i486__} %{posix:-D_POSIX_SOURCE} %{pthread:-D_REENTRANT} - -*cc1: -%{profile:-p} - -*cc1plus: - - -*endfile: -%{!shared:crtend.o%s} %{shared:crtendS.o%s} crtn.o%s - -*link: --m elf_i386 %{shared:-shared} %{!shared: %{!ibcs: %{!static: %{rdynamic:-export-dynamic} %{!dynamic-linker:-dynamic-linker /lib/ld-linux.so.2}} %{static:-static}}} - -*lib: -%{!shared: %{pthread:-lpthread} %{profile:-lc_p} %{!profile: -lc}} - -*libgcc: --lgcc - -*startfile: -%{!shared: %{pg:gcrt1.o%s} %{!pg:%{p:gcrt1.o%s} %{!p:%{profile:gcrt1.o%s} %{!profile:crt1.o%s}}}} crti.o%s %{!shared:crtbegin.o%s} %{shared:crtbeginS.o%s} - -*switches_need_spaces: - - -*signed_char: -%{funsigned-char:-D__CHAR_UNSIGNED__} - -*predefines: --D__ELF__ -Dunix -Di386 -Dlinux -Asystem(unix) -Asystem(posix) -Acpu(i386) -Amachine(i386) - -*cross_compile: -0 - -*multilib: -. ; - ------------------------------------------------------------------------ - -Things get a bit more complicated if you have GNU libc installed in some -other place than /usr, i.e., if you do not want to use it instead of the old -libc. In this case the needed startup files and libraries are not found in -the regular places. So the specs file must tell the compiler and linker -exactly what to use. - -Version 2.7.2.3 does and future versions of GCC will automatically -provide the correct specs. - - -2.7. Looking through the shared libc file I haven't found the - functions `stat', `lstat', `fstat', and `mknod' and while - linking on my Linux system I get error messages. How is - this supposed to work? - -{RM} Believe it or not, stat and lstat (and fstat, and mknod) are supposed -to be undefined references in libc.so.6! Your problem is probably a missing -or incorrect /usr/lib/libc.so file; note that this is a small text file now, -not a symlink to libc.so.6. It should look something like this: - -GROUP ( libc.so.6 libc_nonshared.a ) - - -2.8. When I run an executable on one system which I compiled on - another, I get dynamic linker errors. Both systems have the same - version of glibc installed. What's wrong? - -{ZW} Glibc on one of these systems was compiled with gcc 2.7 or 2.8, the -other with egcs (any version). Egcs has functions in its internal -`libgcc.a' to support exception handling with C++. They are linked into -any program or dynamic library compiled with egcs, whether it needs them or -not. Dynamic libraries then turn around and export those functions again -unless special steps are taken to prevent them. - -When you link your program, it resolves its references to the exception -functions to the ones exported accidentally by libc.so. That works fine as -long as libc has those functions. On the other system, libc doesn't have -those functions because it was compiled by gcc 2.8, and you get undefined -symbol errors. The symbols in question are named things like -`__register_frame_info'. - -For glibc 2.0, the workaround is to not compile libc with egcs. We've also -incorporated a patch which should prevent the EH functions sneaking into -libc. It doesn't matter what compiler you use to compile your program. - -For glibc 2.1, we've chosen to do it the other way around: libc.so -explicitly provides the EH functions. This is to prevent other shared -libraries from doing it. - -{UD} Starting with glibc 2.1.1 you can compile glibc with gcc 2.8.1 or -newer since we have explicitly add references to the functions causing the -problem. But you nevertheless should use EGCS for other reasons -(see question 1.2). - -{GK} On some Linux distributions for PowerPC, you can see this when you have -built gcc or egcs from the Web sources (gcc versions 2.95 or earlier), then -re-built glibc. This happens because in these versions of gcc, exception -handling is implemented using an older method; the people making the -distributions are a little ahead of their time. - -A quick solution to this is to find the libgcc.a file that came with the -distribution (it would have been installed under /usr/lib/gcc-lib), do -`ar x libgcc.a frame.o' to get the frame.o file out, and add a line saying -`LDLIBS-c.so += frame.o' to the file `configparms' in the directory you're -building in. You can check you've got the right `frame.o' file by running -`nm frame.o' and checking that it has the symbols defined that you're -missing. - -This will let you build glibc with the C compiler. The C++ compiler -will still be binary incompatible with any C++ shared libraries that -you got with your distribution. - - -2.9. How can I compile gcc 2.7.2.1 from the gcc source code using - glibc 2.x? - -{AJ} There's only correct support for glibc 2.0.x in gcc 2.7.2.3 or later. -But you should get at least gcc 2.95.3 (or later versions) anyway - - -2.10. The `gencat' utility cannot process the catalog sources which - were used on my Linux libc5 based system. Why? - -{UD} The `gencat' utility provided with glibc complies to the XPG standard. -The older Linux version did not obey the standard, so they are not -compatible. - -To ease the transition from the Linux version some of the non-standard -features are also present in the `gencat' program of GNU libc. This mainly -includes the use of symbols for the message number and the automatic -generation of header files which contain the needed #defines to map the -symbols to integers. - -Here is a simple SED script to convert at least some Linux specific catalog -files to the XPG4 form: - ------------------------------------------------------------------------ -# Change catalog source in Linux specific format to standard XPG format. -# Ulrich Drepper <drepper@redhat.com>, 1996. -# -/^\$ #/ { - h - s/\$ #\([^ ]*\).*/\1/ - x - s/\$ #[^ ]* *\(.*\)/\$ \1/ -} - -/^# / { - s/^# \(.*\)/\1/ - G - s/\(.*\)\n\(.*\)/\2 \1/ -} ------------------------------------------------------------------------ - - -2.11. Programs using libc have their messages translated, but other - behavior is not localized (e.g. collating order); why? - -{ZW} Translated messages are automatically installed, but the locale -database that controls other behaviors is not. You need to run localedef to -install this database, after you have run `make install'. For example, to -set up the French Canadian locale, simply issue the command - - localedef -i fr_CA -f ISO-8859-1 fr_CA - -Please see localedata/README in the source tree for further details. - - -2.12. I have set up /etc/nis.conf, and the Linux libc 5 with NYS - works great. But the glibc NIS+ doesn't seem to work. - -{TK} The glibc NIS+ implementation uses a /var/nis/NIS_COLD_START file for -storing information about the NIS+ server and their public keys, because the -nis.conf file does not contain all the necessary information. You have to -copy a NIS_COLD_START file from a Solaris client (the NIS_COLD_START file is -byte order independent) or generate it with nisinit from the nis-tools -package; available at - - http://www.suse.de/~kukuk/linux/nisplus.html - - -2.13. I have killed ypbind to stop using NIS, but glibc - continues using NIS. - -{TK} For faster NIS lookups, glibc uses the /var/yp/binding/ files from -ypbind. ypbind 3.3 and older versions don't always remove these files, so -glibc will continue to use them. Other BSD versions seem to work correctly. -Until ypbind 3.4 is released, you can find a patch at - - <ftp://ftp.kernel.org/pub/linux/utils/net/NIS/ypbind-3.3-glibc4.diff.gz> - - -2.14. Under Linux/Alpha, I always get "do_ypcall: clnt_call: - RPC: Unable to receive; errno = Connection refused" when using NIS. - -{TK} You need a ypbind version which is 64bit clean. Some versions are not -64bit clean. A 64bit clean implementation is ypbind-mt. For ypbind 3.3, -you need the patch from ftp.kernel.org (See the previous question). I don't -know about other versions. - - -2.15. After installing glibc name resolving doesn't work properly. - -{AJ} You probably should read the manual section describing nsswitch.conf -(just type `info libc "NSS Configuration File"'). The NSS configuration -file is usually the culprit. - - -2.16. How do I create the databases for NSS? - -{AJ} If you have an entry "db" in /etc/nsswitch.conf you should also create -the database files. The glibc sources contain a Makefile which does the -necessary conversion and calls to create those files. The file is -`db-Makefile' in the subdirectory `nss' and you can call it with `make -f -db-Makefile'. Please note that not all services are capable of using a -database. Currently passwd, group, ethers, protocol, rpc, services shadow -and netgroup are implemented. See also question 2.31. - - -2.17. I have /usr/include/net and /usr/include/scsi as symlinks - into my Linux source tree. Is that wrong? - -{PB} This was necessary for libc5, but is not correct when using glibc. -Including the kernel header files directly in user programs usually does not -work (see question 3.5). glibc provides its own <net/*> and <scsi/*> header -files to replace them, and you may have to remove any symlink that you have -in place before you install glibc. However, /usr/include/asm and -/usr/include/linux should remain as they were. - - -2.18. Programs like `logname', `top', `uptime' `users', `w' and - `who', show incorrect information about the (number of) - users on my system. Why? - -{MK} See question 3.2. - - -2.19. After upgrading to glibc 2.1 with symbol versioning I get - errors about undefined symbols. What went wrong? - -{AJ} The problem is caused either by wrong program code or tools. In the -versioned libc a lot of symbols are now local that were global symbols in -previous versions. It seems that programs linked against older versions -often accidentally used libc global variables -- something that should not -happen. - -The only way to fix this is to recompile your program. Sorry, that's the -price you might have to pay once for quite a number of advantages with -symbol versioning. - - -2.20. When I start the program XXX after upgrading the library - I get - XXX: Symbol `_sys_errlist' has different size in shared - object, consider re-linking - Why? What should I do? - -{UD} As the message says, relink the binary. The problem is that a few -symbols from the library can change in size and there is no way to avoid -this. _sys_errlist is a good example. Occasionally there are new error -numbers added to the kernel and this must be reflected at user level, -breaking programs that refer to them directly. - -Such symbols should normally not be used at all. There are mechanisms to -avoid using them. In the case of _sys_errlist, there is the strerror() -function which should _always_ be used instead. So the correct fix is to -rewrite that part of the application. - -In some situations (especially when testing a new library release) it might -be possible that a symbol changed size when that should not have happened. -So in case of doubt report such a warning message as a problem. - - -2.21. What do I need for C++ development? - -{HJ,AJ} You need either egcs 1.1 which comes directly with libstdc++ or -gcc-2.8.1 together with libstdc++ 2.8.1.1. egcs 1.1 has the better C++ -support and works directly with glibc 2.1. If you use gcc-2.8.1 with -libstdc++ 2.8.1.1, you need to modify libstdc++ a bit. A patch is available -as: - <ftp://alpha.gnu.org/gnu/libstdc++-2.8.1.1-glibc2.1-diff.gz> - -Please note that libg++ 2.7.2 (and the Linux Versions 2.7.2.x) doesn't work -very well with the GNU C library due to vtable thunks. If you're upgrading -from glibc 2.0.x to 2.1 you have to recompile libstdc++ since the library -compiled for 2.0 is not compatible due to the new Large File Support (LFS) -in version 2.1. - -{UD} But since in the case of a shared libstdc++ the version numbers should -be different existing programs will continue to work. - - -2.22. Even statically linked programs need some shared libraries - which is not acceptable for me. What can I do? - -{AJ} NSS (for details just type `info libc "Name Service Switch"') won't -work properly without shared libraries. NSS allows using different services -(e.g. NIS, files, db, hesiod) by just changing one configuration file -(/etc/nsswitch.conf) without relinking any programs. The only disadvantage -is that now static libraries need to access shared libraries. This is -handled transparently by the GNU C library. - -A solution is to configure glibc with --enable-static-nss. In this case you -can create a static binary that will use only the services dns and files -(change /etc/nsswitch.conf for this). You need to link explicitly against -all these services. For example: - - gcc -static test-netdb.c -o test-netdb \ - -Wl,--start-group -lc -lnss_files -lnss_dns -lresolv -Wl,--end-group - -The problem with this approach is that you've got to link every static -program that uses NSS routines with all those libraries. - -{UD} In fact, one cannot say anymore that a libc compiled with this -option is using NSS. There is no switch anymore. Therefore it is -*highly* recommended *not* to use --enable-static-nss since this makes -the behaviour of the programs on the system inconsistent. - - -2.23. I just upgraded my Linux system to glibc and now I get - errors whenever I try to link any program. - -{ZW} This happens when you have installed glibc as the primary C library but -have stray symbolic links pointing at your old C library. If the first -`libc.so' the linker finds is libc 5, it will use that. Your program -expects to be linked with glibc, so the link fails. - -The most common case is that glibc put its `libc.so' in /usr/lib, but there -was a `libc.so' from libc 5 in /lib, which gets searched first. To fix the -problem, just delete /lib/libc.so. You may also need to delete other -symbolic links in /lib, such as /lib/libm.so if it points to libm.so.5. - -{AJ} The perl script test-installation.pl which is run as last step during -an installation of glibc that is configured with --prefix=/usr should help -detect these situations. If the script reports problems, something is -really screwed up. - - -2.24. When I use nscd the machine freezes. - -{UD} You cannot use nscd with Linux 2.0.*. There is functionality missing -in the kernel and work-arounds are not suitable. Besides, some parts of the -kernel are too buggy when it comes to using threads. - -If you need nscd, you have to use at least a 2.1 kernel. - -Note that I have at this point no information about any other platform. - - -2.25. I need lots of open files. What do I have to do? - -{AJ} This is at first a kernel issue. The kernel defines limits with -OPEN_MAX the number of simultaneous open files and with FD_SETSIZE the -number of used file descriptors. You need to change these values in your -kernel and recompile the kernel so that the kernel allows more open -files. You don't necessarily need to recompile the GNU C library since the -only place where OPEN_MAX and FD_SETSIZE is really needed in the library -itself is the size of fd_set which is used by select. - -The GNU C library is now select free. This means it internally has no -limits imposed by the `fd_set' type. Instead all places where the -functionality is needed the `poll' function is used. - -If you increase the number of file descriptors in the kernel you don't need -to recompile the C library. - -{UD} You can always get the maximum number of file descriptors a process is -allowed to have open at any time using - - number = sysconf (_SC_OPEN_MAX); - -This will work even if the kernel limits change. - - -2.26. How do I get the same behavior on parsing /etc/passwd and - /etc/group as I have with libc5 ? - -{TK} The name switch setup in /etc/nsswitch.conf selected by most Linux -distributions does not support +/- and netgroup entries in the files like -/etc/passwd. Though this is the preferred setup some people might have -setups coming over from the libc5 days where it was the default to recognize -lines like this. To get back to the old behaviour one simply has to change -the rules for passwd, group, and shadow in the nsswitch.conf file as -follows: - -passwd: compat -group: compat -shadow: compat - -passwd_compat: nis -group_compat: nis -shadow_compat: nis - - -2.27. What needs to be recompiled when upgrading from glibc 2.0 to glibc - 2.1? - -{AJ,CG} If you just upgrade the glibc from 2.0.x (x <= 7) to 2.1, binaries -that have been linked against glibc 2.0 will continue to work. - -If you compile your own binaries against glibc 2.1, you also need to -recompile some other libraries. The problem is that libio had to be changed -and therefore libraries that are based or depend on the libio of glibc, -e.g. ncurses, slang and most C++ libraries, need to be recompiled. If you -experience strange segmentation faults in your programs linked against glibc -2.1, you might need to recompile your libraries. - -Another problem is that older binaries that were linked statically against -glibc 2.0 will reference the older nss modules (libnss_files.so.1 instead of -libnss_files.so.2), so don't remove them. Also, the old glibc-2.0 compiled -static libraries (libfoo.a) which happen to depend on the older libio -behavior will be broken by the glibc 2.1 upgrade. We plan to produce a -compatibility library that people will be able to link in if they want -to compile a static library generated against glibc 2.0 into a program -on a glibc 2.1 system. You just add -lcompat and you should be fine. - -The glibc-compat add-on will provide the libcompat.a library, the older -nss modules, and a few other files. Together, they should make it -possible to do development with old static libraries on a glibc 2.1 -system. This add-on is still in development. You can get it from - <ftp://alpha.gnu.org/gnu/glibc/glibc-compat-2.1.tar.gz> -but please keep in mind that it is experimental. - - -2.28. Why is extracting files via tar so slow? - -{AJ} Extracting of tar archives might be quite slow since tar has to look up -userid and groupids and doesn't cache negative results. If you have nis or -nisplus in your /etc/nsswitch.conf for the passwd and/or group database, -each file extractions needs a network connection. There are two possible -solutions: - -- do you really need NIS/NIS+ (some Linux distributions add by default - nis/nisplus even if it's not needed)? If not, just remove the entries. - -- if you need NIS/NIS+, use the Name Service Cache Daemon nscd that comes - with glibc 2.1. - - -2.29. Compiling programs I get parse errors in libio.h (e.g. "parse error - before `_IO_seekoff'"). How should I fix this? - -{AJ} You might get the following errors when upgrading to glibc 2.1: - - In file included from /usr/include/stdio.h:57, - from ... - /usr/include/libio.h:335: parse error before `_IO_seekoff' - /usr/include/libio.h:335: parse error before `_G_off64_t' - /usr/include/libio.h:336: parse error before `_IO_seekpos' - /usr/include/libio.h:336: parse error before `_G_fpos64_t' - -The problem is a wrong _G_config.h file in your include path. The -_G_config.h file that comes with glibc 2.1 should be used and not one from -libc5 or from a compiler directory. To check which _G_config.h file the -compiler uses, compile your program with `gcc -E ...|grep G_config.h' and -remove that file. Your compiler should pick up the file that has been -installed by glibc 2.1 in your include directory. - - -2.30. After upgrading to glibc 2.1, libraries that were compiled against - glibc 2.0.x don't work anymore. - -{AJ} See question 2.27. - - -2.31. What happened to the Berkeley DB libraries? Can I still use db - in /etc/nsswitch.conf? - -{AJ} Due to too many incompatible changes in disk layout and API of Berkeley -DB and a too tight coupling of libc and libdb, the db library has been -removed completely from glibc 2.2. The only place that really used the -Berkeley DB was the NSS db module. - -The NSS db module has been rewritten to support a number of different -versions of Berkeley DB for the NSS db module. Currently the releases 2.x -and 3.x of Berkeley DB are supported. The older db 1.85 library is not -supported. You can use the version from glibc 2.1.x or download a version -from Sleepycat Software (http://www.sleepycat.com). The library has to be -compiled as shared library and installed in the system lib directory -(normally /lib). The library needs to have a special soname to be found by -the NSS module. - -If public structures change in a new Berkeley db release, this needs to be -reflected in glibc. - -Currently the code searches for libraries with a soname of "libdb.so.3" -(that's the name from db 2.4.14 which comes with glibc 2.1.x) and -"libdb-3.0.so" (the name used by db 3.0.55 as default). - -The nss_db module is now in a separate package since it requires a database -library being available. - - -2.32. What has do be done when upgrading to glibc 2.2? - -{AJ} The upgrade to glibc 2.2 should run smoothly, there's in general no -need to recompile programs or libraries. Nevertheless, some changes might -be needed after upgrading: -- The utmp daemon has been removed and is not supported by glibc anymore. - If it has been in use, it should be switched off. -- Programs using IPv6 have to be recompiled due to incompatible changes in - sockaddr_in6 by the IPv6 working group. -- The Berkeley db libraries have been removed (for details see question 2.31). -- The format of the locale files has changed, all locales should be - regenerated with localedef. All statically linked applications which use - i18n should be recompiled, otherwise they'll not be localized. -- glibc comes with a number of new applications. For example ldconfig has - been implemented for glibc, the libc5 version of ldconfig is not needed - anymore. -- There's no more K&R compatibility in the glibc headers. The GNU C library - requires a C compiler that handles especially prototypes correctly. - Especially gcc -traditional will not work with glibc headers. - -Please read also the NEWS file which is the authoritative source for this -and gives more details for some topics. - - -2.33. The makefiles want to do a CVS commit. - -{} Removed. Does not apply anymore. - - -2.34. When compiling C++ programs, I get a compilation error in streambuf.h. - -{BH} You are using g++ 2.95.2? After upgrading to glibc 2.2, you need to -apply a patch to the include files in /usr/include/g++, because the fpos_t -type has changed in glibc 2.2. The patch is at - - http://www.haible.de/bruno/gccinclude-glibc-2.2-compat.diff - - -2.35. When recompiling GCC, I get compilation errors in libio. - -{BH} You are trying to recompile gcc 2.95.2? Use gcc 2.95.3 instead. -This version is needed because the fpos_t type and a few libio internals -have changed in glibc 2.2, and gcc 2.95.3 contains a corresponding patch. - - -2.36. Why shall glibc never get installed on GNU/Linux systems in -/usr/local? - -{AJ} The GNU C compiler treats /usr/local/include and /usr/local/lib in a -special way, these directories will be searched before the system -directories. Since on GNU/Linux the system directories /usr/include and -/usr/lib contain a --- possibly different --- version of glibc and mixing -certain files from different glibc installations is not supported and will -break, you risk breaking your complete system. If you want to test a glibc -installation, use another directory as argument to --prefix. If you like to -install this glibc version as default version, overriding the existing one, -use --prefix=/usr and everything will go in the right places. - - -2.37. When recompiling GCC, I get compilation errors in libstdc++. - -{BH} You are trying to recompile gcc 3.2? You need to patch gcc 3.2, -because some last minute changes were made in glibc 2.3 which were not -known when gcc 3.2 was released. The patch is at - - http://www.haible.de/bruno/gcc-3.2-glibc-2.3-compat.diff - - -. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - -3. Source and binary incompatibilities, and what to do about them - -3.1. I expect GNU libc to be 100% source code compatible with - the old Linux based GNU libc. Why isn't it like this? - -{DMT,UD} Not every extension in Linux libc's history was well thought-out. -In fact it had a lot of problems with standards compliance and with -cleanliness. With the introduction of a new version number these errors can -now be corrected. Here is a list of the known source code -incompatibilities: - -* _GNU_SOURCE: glibc does not make the GNU extensions available - automatically. If a program depends on GNU extensions or some - other non-standard functionality, it is necessary to compile it - with the C compiler option -D_GNU_SOURCE, or better, to put - `#define _GNU_SOURCE' at the beginning of your source files, before - any C library header files are included. This difference normally - manifests itself in the form of missing prototypes and/or data type - definitions. Thus, if you get such errors, the first thing you - should do is try defining _GNU_SOURCE and see if that makes the - problem go away. - - For more information consult the file `NOTES' in the GNU C library - sources. - -* reboot(): GNU libc sanitizes the interface of reboot() to be more - compatible with the interface used on other OSes. reboot() as - implemented in glibc takes just one argument. This argument - corresponds to the third argument of the Linux reboot system call. - That is, a call of the form reboot(a, b, c) needs to be changed into - reboot(c). Beside this the header <sys/reboot.h> defines the needed - constants for the argument. These RB_* constants should be used - instead of the cryptic magic numbers. - -* swapon(): the interface of this function didn't change, but the - prototype is in a separate header file <sys/swap.h>. This header - file also provides the SWAP_* constants defined by <linux/swap.h>; - you should use them for the second argument to swapon(). - -* errno: If a program uses the variable "errno", then it _must_ - include <errno.h>. The old libc often (erroneously) declared this - variable implicitly as a side-effect of including other libc header - files. glibc is careful to avoid such namespace pollution, which, - in turn, means that you really need to include the header files that - you depend on. This difference normally manifests itself in the - form of the compiler complaining about references to an undeclared - symbol "errno". - -* Linux-specific syscalls: All Linux system calls now have appropriate - library wrappers and corresponding declarations in various header files. - This is because the syscall() macro that was traditionally used to - work around missing syscall wrappers are inherently non-portable and - error-prone. The following table lists all the new syscall stubs, - the header-file declaring their interface and the system call name. - - syscall name: wrapper name: declaring header file: - ------------- ------------- ---------------------- - bdflush bdflush <sys/kdaemon.h> - syslog ksyslog_ctl <sys/klog.h> - -* lpd: Older versions of lpd depend on a routine called _validuser(). - The library does not provide this function, but instead provides - __ivaliduser() which has a slightly different interface. Simply - upgrading to a newer lpd should fix this problem (e.g., the 4.4BSD - lpd is known to be working). - -* resolver functions/BIND: like on many other systems the functions of - the resolver library are not included in libc itself. There is a - separate library libresolv. If you get undefined symbol errors for - symbols starting with `res_*' simply add -lresolv to your linker - command line. - -* the `signal' function's behavior corresponds to the BSD semantic and - not the SysV semantic as it was in libc-5. The interface on all GNU - systems shall be the same and BSD is the semantic of choice. To use - the SysV behavior simply use `sysv_signal', or define _XOPEN_SOURCE. - See question 3.7 for details. - - -3.2. Why does getlogin() always return NULL on my Linux box? - -{UD} The GNU C library has a format for the UTMP and WTMP file which differs -from what your system currently has. It was extended to fulfill the needs -of the next years when IPv6 is introduced. The record size is different and -some fields have different positions. The files written by functions from -the one library cannot be read by functions from the other library. Sorry, -but this is what a major release is for. It's better to have a cut now than -having no means to support the new techniques later. - - -3.3. Where are the DST_* constants found in <sys/time.h> on many - systems? - -{UD} These constants come from the old BSD days and are not used anymore -(libc5 does not actually implement the handling although the constants are -defined). - -Instead GNU libc contains zone database support and compatibility code for -POSIX TZ environment variable handling. For former is very much preferred -(see question 4.3). - - -3.4. The prototypes for `connect', `accept', `getsockopt', - `setsockopt', `getsockname', `getpeername', `send', - `sendto', and `recvfrom' are different in GNU libc from - any other system I saw. This is a bug, isn't it? - -{UD} No, this is no bug. This version of GNU libc already follows the new -Single Unix specifications (and I think the POSIX.1g draft which adopted the -solution). The type for a parameter describing a size is now `socklen_t', a -new type. - - -3.5. On Linux I've got problems with the declarations in Linux - kernel headers. - -{UD,AJ} On Linux, the use of kernel headers is reduced to the minimum. This -gives Linus the ability to change the headers more freely. Also, user -programs are now insulated from changes in the size of kernel data -structures. - -For example, the sigset_t type is 32 or 64 bits wide in the kernel. In -glibc it is 1024 bits wide. This guarantees that when the kernel gets a -bigger sigset_t (for POSIX.1e realtime support, say) user programs will not -have to be recompiled. Consult the header files for more information about -the changes. - -Therefore you shouldn't include Linux kernel header files directly if glibc -has defined a replacement. Otherwise you might get undefined results because -of type conflicts. - - -3.6. I don't include any kernel headers myself but the compiler - still complains about redeclarations of types in the kernel - headers. - -{UD} The kernel headers before Linux 2.1.61 and 2.0.32 don't work correctly -with glibc. Compiling C programs is possible in most cases but C++ programs -have (due to the change of the name lookups for `struct's) problems. One -prominent example is `struct fd_set'. - -There might be some problems left but 2.1.61/2.0.32 fix most of the known -ones. See the BUGS file for other known problems. - - -3.7. Why don't signals interrupt system calls anymore? - -{ZW} By default GNU libc uses the BSD semantics for signal(), unlike Linux -libc 5 which used System V semantics. This is partially for compatibility -with other systems and partially because the BSD semantics tend to make -programming with signals easier. - -There are three differences: - -* BSD-style signals that occur in the middle of a system call do not - affect the system call; System V signals cause the system call to - fail and set errno to EINTR. - -* BSD signal handlers remain installed once triggered. System V signal - handlers work only once, so one must reinstall them each time. - -* A BSD signal is blocked during the execution of its handler. In other - words, a handler for SIGCHLD (for example) does not need to worry about - being interrupted by another SIGCHLD. It may, however, be interrupted - by other signals. - -There is general consensus that for `casual' programming with signals, the -BSD semantics are preferable. You don't need to worry about system calls -returning EINTR, and you don't need to worry about the race conditions -associated with one-shot signal handlers. - -If you are porting an old program that relies on the old semantics, you can -quickly fix the problem by changing signal() to sysv_signal() throughout. -Alternatively, define _XOPEN_SOURCE before including <signal.h>. - -For new programs, the sigaction() function allows you to specify precisely -how you want your signals to behave. All three differences listed above are -individually switchable on a per-signal basis with this function. - -If all you want is for one specific signal to cause system calls to fail and -return EINTR (for example, to implement a timeout) you can do this with -siginterrupt(). - - -3.8. I've got errors compiling code that uses certain string - functions. Why? - -{AJ} glibc 2.1 has special string functions that are faster than the normal -library functions. Some of the functions are additionally implemented as -inline functions and others as macros. This might lead to problems with -existing codes but it is explicitly allowed by ISO C. - -The optimized string functions are only used when compiling with -optimizations (-O1 or higher). The behavior can be changed with two feature -macros: - -* __NO_STRING_INLINES: Don't do any string optimizations. -* __USE_STRING_INLINES: Use assembly language inline functions (might - increase code size dramatically). - -Since some of these string functions are now additionally defined as macros, -code like "char *strncpy();" doesn't work anymore (and is unnecessary, since -<string.h> has the necessary declarations). Either change your code or -define __NO_STRING_INLINES. - -{UD} Another problem in this area is that gcc still has problems on machines -with very few registers (e.g., ix86). The inline assembler code can require -almost all the registers and the register allocator cannot always handle -this situation. - -One can disable the string optimizations selectively. Instead of writing - - cp = strcpy (foo, "lkj"); - -one can write - - cp = (strcpy) (foo, "lkj"); - -This disables the optimization for that specific call. - - -3.9. I get compiler messages "Initializer element not constant" with - stdin/stdout/stderr. Why? - -{RM,AJ} Constructs like: - static FILE *InPtr = stdin; - -lead to this message. This is correct behaviour with glibc since stdin is -not a constant expression. Please note that a strict reading of ISO C does -not allow above constructs. - -One of the advantages of this is that you can assign to stdin, stdout, and -stderr just like any other global variable (e.g. `stdout = my_stream;'), -which can be very useful with custom streams that you can write with libio -(but beware this is not necessarily portable). The reason to implement it -this way were versioning problems with the size of the FILE structure. - -To fix those programs you've got to initialize the variable at run time. -This can be done, e.g. in main, like: - - static FILE *InPtr; - int main(void) - { - InPtr = stdin; - } - -or by constructors (beware this is gcc specific): - - static FILE *InPtr; - static void inPtr_construct (void) __attribute__((constructor)); - static void inPtr_construct (void) { InPtr = stdin; } - - -3.10. I can't compile with gcc -traditional (or - -traditional-cpp). Why? - -{AJ} glibc2 does break -traditional and -traditonal-cpp - and will continue -to do so. For example constructs of the form: - - enum {foo - #define foo foo - } - -are useful for debugging purposes (you can use foo with your debugger that's -why we need the enum) and for compatibility (other systems use defines and -check with #ifdef). - - -3.11. I get some errors with `gcc -ansi'. Isn't glibc ANSI compatible? - -{AJ} The GNU C library is compatible with the ANSI/ISO C standard. If -you're using `gcc -ansi', the glibc includes which are specified in the -standard follow the standard. The ANSI/ISO C standard defines what has to be -in the include files - and also states that nothing else should be in the -include files (btw. you can still enable additional standards with feature -flags). - -The GNU C library is conforming to ANSI/ISO C - if and only if you're only -using the headers and library functions defined in the standard. - - -3.12. I can't access some functions anymore. nm shows that they do - exist but linking fails nevertheless. - -{AJ} With the introduction of versioning in glibc 2.1 it is possible to -export only those identifiers (functions, variables) that are really needed -by application programs and by other parts of glibc. This way a lot of -internal interfaces are now hidden. nm will still show those identifiers -but marking them as internal. ISO C states that identifiers beginning with -an underscore are internal to the libc. An application program normally -shouldn't use those internal interfaces (there are exceptions, -e.g. __ivaliduser). If a program uses these interfaces, it's broken. These -internal interfaces might change between glibc releases or dropped -completely. - - -3.13. When using the db-2 library which comes with glibc is used in - the Perl db modules the testsuite is not passed. This did not - happen with db-1, gdbm, or ndbm. - -{} Removed. Does not apply anymore. - - -3.14. The pow() inline function I get when including <math.h> is broken. - I get segmentation faults when I run the program. - -{UD} Nope, the implementation is correct. The problem is with egcs version -prior to 1.1. I.e., egcs 1.0 to 1.0.3 are all broken (at least on Intel). -If you have to use this compiler you must define __NO_MATH_INLINES before -including <math.h> to prevent the inline functions from being used. egcs 1.1 -fixes the problem. I don't know about gcc 2.8 and 2.8.1. - - -3.15. The sys/sem.h file lacks the definition of `union semun'. - -{UD} Nope. This union has to be provided by the user program. Former glibc -versions defined this but it was an error since it does not make much sense -when thinking about it. The standards describing the System V IPC functions -define it this way and therefore programs must be adopted. - - -3.16. Why has <netinet/ip_fw.h> disappeared? - -{AJ} The corresponding Linux kernel data structures and constants are -totally different in Linux 2.0 and Linux 2.2. This situation has to be -taken care in user programs using the firewall structures and therefore -those programs (ipfw is AFAIK the only one) should deal with this problem -themselves. - - -3.17. I get floods of warnings when I use -Wconversion and include - <string.h> or <math.h>. - -{ZW} <string.h> and <math.h> intentionally use prototypes to override -argument promotion. -Wconversion warns about all these. You can safely -ignore the warnings. - --Wconversion isn't really intended for production use, only for shakedown -compiles after converting an old program to standard C. - - -3.18. After upgrading to glibc 2.1, I receive errors about - unresolved symbols, like `_dl_initial_searchlist' and can not - execute any binaries. What went wrong? - -{AJ} This normally happens if your libc and ld (dynamic linker) are from -different releases of glibc. For example, the dynamic linker -/lib/ld-linux.so.2 comes from glibc 2.0.x, but the version of libc.so.6 is -from glibc 2.1. - -The path /lib/ld-linux.so.2 is hardcoded in every glibc2 binary but -libc.so.6 is searched via /etc/ld.so.cache and in some special directories -like /lib and /usr/lib. If you run configure with another prefix than /usr -and put this prefix before /lib in /etc/ld.so.conf, your system will break. - -So what can you do? Either of the following should work: - -* Run `configure' with the same prefix argument you've used for glibc 2.0.x - so that the same paths are used. -* Replace /lib/ld-linux.so.2 with a link to the dynamic linker from glibc - 2.1. - -You can even call the dynamic linker by hand if everything fails. You've -got to set LD_LIBRARY_PATH so that the corresponding libc is found and also -need to provide an absolute path to your binary: - - LD_LIBRARY_PATH=<path-where-libc.so.6-lives> \ - <path-where-corresponding-dynamic-linker-lives>/ld-linux.so.2 \ - <path-to-binary>/binary - -For example `LD_LIBRARY_PATH=/libold /libold/ld-linux.so.2 /bin/mv ...' -might be useful in fixing a broken system (if /libold contains dynamic -linker and corresponding libc). - -With that command line no path is used. To further debug problems with the -dynamic linker, use the LD_DEBUG environment variable, e.g. -`LD_DEBUG=help echo' for the help text. - -If you just want to test this release, don't put the lib directory in -/etc/ld.so.conf. You can call programs directly with full paths (as above). -When compiling new programs against glibc 2.1, you've got to specify the -correct paths to the compiler (option -I with gcc) and linker (options ---dynamic-linker, -L and --rpath). - - -3.19. bonnie reports that char i/o with glibc 2 is much slower than with - libc5. What can be done? - -{AJ} The GNU C library uses thread safe functions by default and libc5 used -non thread safe versions. The non thread safe functions have in glibc the -suffix `_unlocked', for details check <stdio.h>. Using `putc_unlocked' etc. -instead of `putc' should give nearly the same speed with bonnie (bonnie is a -benchmark program for measuring disk access). - - -3.20. Programs compiled with glibc 2.1 can't read db files made with glibc - 2.0. What has changed that programs like rpm break? - -{} Removed. Does not apply anymore. - - -3.21. Autoconf's AC_CHECK_FUNC macro reports that a function exists, but - when I try to use it, it always returns -1 and sets errno to ENOSYS. - -{ZW} You are using a 2.0 Linux kernel, and the function you are trying to -use is only implemented in 2.1/2.2. Libc considers this to be a function -which exists, because if you upgrade to a 2.2 kernel, it will work. One -such function is sigaltstack. - -Your program should check at runtime whether the function works, and -implement a fallback. Note that Autoconf cannot detect unimplemented -functions in other systems' C libraries, so you need to do this anyway. - - -3.22. My program segfaults when I call fclose() on the FILE* returned - from setmntent(). Is this a glibc bug? - -{GK} No. Don't do this. Use endmntent(), that's what it's for. - -In general, you should use the correct deallocation routine. For instance, -if you open a file using fopen(), you should deallocate the FILE * using -fclose(), not free(), even though the FILE * is also a pointer. - -In the case of setmntent(), it may appear to work in most cases, but it -won't always work. Unfortunately, for compatibility reasons, we can't -change the return type of setmntent() to something other than FILE *. - - -3.23. I get "undefined reference to `atexit'" - -{UD} This means that your installation is somehow broken. The situation is -the same as for 'stat', 'fstat', etc (see question 2.7). Investigate why the -linker does not pick up libc_nonshared.a. - -If a similar message is issued at runtime this means that the application or -DSO is not linked against libc. This can cause problems since 'atexit' is -not exported anymore. - - -. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - -4. Miscellaneous - -4.1. After I changed configure.in I get `Autoconf version X.Y. - or higher is required for this script'. What can I do? - -{UD} You have to get the specified autoconf version (or a later one) -from your favorite mirror of ftp.gnu.org. - - -4.2. When I try to compile code which uses IPv6 headers and - definitions on my Linux 2.x.y system I am in trouble. - Nothing seems to work. - -{UD} The problem is that IPv6 development still has not reached a point -where the headers are stable. There are still lots of incompatible changes -made and the libc headers have to follow. - -{PB} The 2.1 release of GNU libc aims to comply with the current versions of -all the relevant standards. The IPv6 support libraries for older Linux -systems used a different naming convention and so code written to work with -them may need to be modified. If the standards make incompatible changes in -the future then the libc may need to change again. - -IPv6 will not work with a 2.0.x kernel. When kernel 2.2 is released it -should contain all the necessary support; until then you should use the -latest 2.1.x release you can find. As of 98/11/26 the currently recommended -kernel for IPv6 is 2.1.129. - -Also, as of the 2.1 release the IPv6 API provided by GNU libc is not -100% complete. - - -4.3. When I set the timezone by setting the TZ environment variable - to EST5EDT things go wrong since glibc computes the wrong time - from this information. - -{UD} The problem is that people still use the braindamaged POSIX method to -select the timezone using the TZ environment variable with a format EST5EDT -or whatever. People, if you insist on using TZ instead of the timezone -database (see below), read the POSIX standard, the implemented behaviour is -correct! What you see is in fact the result of the decisions made while -POSIX.1 was created. We've only implemented the handling of TZ this way to -be POSIX compliant. It is not really meant to be used. - -The alternative approach to handle timezones which is implemented is the -correct one to use: use the timezone database. This avoids all the problems -the POSIX method has plus it is much easier to use. Simply run the tzselect -shell script, answer the question and use the name printed in the end by -making a symlink /etc/localtime pointing to /usr/share/zoneinfo/NAME (NAME -is the returned value from tzselect). That's all. You never again have to -worry. - -So, please avoid sending bug reports about time related problems if you use -the POSIX method and you have not verified something is really broken by -reading the POSIX standards. - - -4.4. What other sources of documentation about glibc are available? - -{AJ} The FSF has a page about the GNU C library at -<http://www.gnu.org/software/libc/>. The problem data base of open and -solved bugs in GNU libc is available at -<http://www-gnats.gnu.org:8080/cgi-bin/wwwgnats.pl>. Eric Green has written -a HowTo for converting from Linux libc5 to glibc2. The HowTo is accessible -via the FSF page and at <http://www.imaxx.net/~thrytis/glibc>. Frodo -Looijaard describes a different way installing glibc2 as secondary libc at -<http://huizen.dds.nl/~frodol/glibc>. - -Please note that this is not a complete list. - - -4.5. The timezone string for Sydney/Australia is wrong since even when - daylight saving time is in effect the timezone string is EST. - -{UD} The problem for some timezones is that the local authorities decided -to use the term "summer time" instead of "daylight saving time". In this -case the abbreviation character `S' is the same as the standard one. So, -for Sydney we have - - Eastern Standard Time = EST - Eastern Summer Time = EST - -Great! To get this bug fixed convince the authorities to change the laws -and regulations of the country this effects. glibc behaves correctly. - - -4.6. I've build make 3.77 against glibc 2.1 and now make gets - segmentation faults. - -{} Removed. Does not apply anymore, use make 3.79 or newer. - - -4.7. Why do so many programs using math functions fail on my AlphaStation? - -{AO} The functions floor() and floorf() use an instruction that is not -implemented in some old PALcodes of AlphaStations. This may cause -`Illegal Instruction' core dumps or endless loops in programs that -catch these signals. Updating the firmware to a 1999 release has -fixed the problem on an AlphaStation 200 4/166. - - -4.8. The conversion table for character set XX does not match with -what I expect. - -{UD} I don't doubt for a minute that some of the conversion tables contain -errors. We tried the best we can and relied on automatic generation of the -data to prevent human-introduced errors but this still is no guarantee. If -you think you found a problem please send a bug report describing it and -give an authoritive reference. The latter is important since otherwise -the current behaviour is as good as the proposed one. - -Before doing this look through the list of known problem first: - -- the GBK (simplified Chinese) encoding is based on Unicode tables. This - is good. These tables, however, differ slightly from the tables used - by the M$ people. The differences are these [+ Unicode, - M$]: - - +0xA1AA 0x2015 - +0xA844 0x2014 - -0xA1AA 0x2014 - -0xA844 0x2015 - - In addition the Unicode tables contain mappings for the GBK characters - 0xA8BC, 0xA8BF, 0xA989 to 0xA995, and 0xFE50 to 0xFEA0. - -- when mapping from EUC-CN to GBK and vice versa we ignore the fact that - the coded character at position 0xA1A4 maps to different Unicode - characters. Since the iconv() implementation can do whatever it wants - if it cannot directly map a character this is a perfectly good solution - since the semantics and appearance of the character does not change. - - -4.9. How can I find out which version of glibc I am using in the moment? - -{UD} If you want to find out about the version from the command line simply -run the libc binary. This is probably not possible on all platforms but -where it is simply locate the libc DSO and start it as an application. On -Linux like - - /lib/libc.so.6 - -This will produce all the information you need. - -What always will work is to use the API glibc provides. Compile and run the -following little program to get the version information: - -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -#include <stdio.h> -#include <gnu/libc-version.h> -int main (void) { puts (gnu_get_libc_version ()); return 0; } -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ - -This interface can also obviously be used to perform tests at runtime if -this should be necessary. - - -4.10. Context switching with setcontext() does not work from within - signal handlers. - -{DMT} The Linux implementations (IA-64, S390 so far) of setcontext() -supports synchronous context switches only. There are several reasons for -this: - -- UNIX provides no other (portable) way of effecting a synchronous - context switch (also known as co-routine switch). Some versions - support this via setjmp()/longjmp() but this does not work - universally. - -- As defined by the UNIX '98 standard, the only way setcontext() - could trigger an asychronous context switch is if this function - were invoked on the ucontext_t pointer passed as the third argument - to a signal handler. But according to draft 5, XPG6, XBD 2.4.3, - setcontext() is not among the set of routines that may be called - from a signal handler. - -- If setcontext() were to be used for asynchronous context switches, - all kinds of synchronization and re-entrancy issues could arise and - these problems have already been solved by real multi-threading - libraries (e.g., POSIX threads or Linux threads). - -- Synchronous context switching can be implemented entirely in - user-level and less state needs to be saved/restored than for an - asynchronous context switch. It is therefore useful to distinguish - between the two types of context switches. Indeed, some - application vendors are known to use setcontext() to implement - co-routines on top of normal (heavier-weight) pre-emptable threads. - -It should be noted that if someone was dead-bent on using setcontext() -on the third arg of a signal handler, then IA-64 Linux could support -this via a special version of sigaction() which arranges that all -signal handlers start executing in a shim function which takes care of -saving the preserved registers before calling the real signal handler -and restoring them afterwards. In other words, we could provide a -compatibility layer which would support setcontext() for asynchronous -context switches. However, given the arguments above, I don't think -that makes sense. setcontext() provides a decent co-routine interface -and we should just discourage any asynchronous use (which just calls -for trouble at any rate). - - -~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ - -Answers were given by: -{UD} Ulrich Drepper, <drepper@redhat.com> -{DMT} David Mosberger-Tang, <davidm@hpl.hp.com> -{RM} Roland McGrath, <roland@gnu.org> -{AJ} Andreas Jaeger, <aj@suse.de> -{EY} Eric Youngdale, <eric@andante.jic.com> -{PB} Phil Blundell, <Philip.Blundell@pobox.com> -{MK} Mark Kettenis, <kettenis@phys.uva.nl> -{ZW} Zack Weinberg, <zack@rabi.phys.columbia.edu> -{TK} Thorsten Kukuk, <kukuk@suse.de> -{GK} Geoffrey Keating, <geoffk@redhat.com> -{HJ} H.J. Lu, <hjl@gnu.org> -{CG} Cristian Gafton, <gafton@redhat.com> -{AO} Alexandre Oliva, <aoliva@redhat.com> -{BH} Bruno Haible, <haible@clisp.cons.org> -{SM} Steven Munroe, <sjmunroe@us.ibm.com> -{CO} Carlos O'Donell, <carlos@systemhalted.org> - -Local Variables: - mode:outline - outline-regexp:"\\?" - fill-column:76 -End: @@ -1,1701 +0,0 @@ - Frequently Asked Questions about the GNU C Library - -This document tries to answer questions a user might have when installing -and using glibc. Please make sure you read this before sending questions or -bug reports to the maintainers. - -The GNU C library is very complex. The installation process has not been -completely automated; there are too many variables. You can do substantial -damage to your system by installing the library incorrectly. Make sure you -understand what you are undertaking before you begin. - -If you have any questions you think should be answered in this document, -please let me know. - - --drepper@redhat.com - -? Compiling glibc - -?? What systems does the GNU C Library run on? - -{UD} This is difficult to answer. The file `README' lists the architectures -GNU libc was known to run on *at some time*. This does not mean that it -still can be compiled and run on them now. - -The systems glibc is known to work on as of this release, and most probably -in the future, are: - - *-*-gnu GNU Hurd - i[3456]86-*-linux-gnu Linux-2.x on Intel - m68k-*-linux-gnu Linux-2.x on Motorola 680x0 - alpha*-*-linux-gnu Linux-2.x on DEC Alpha - powerpc-*-linux-gnu Linux and MkLinux on PowerPC systems - powerpc64-*-linux-gnu Linux-2.4+ on 64-bit PowerPC systems - sparc-*-linux-gnu Linux-2.x on SPARC - sparc64-*-linux-gnu Linux-2.x on UltraSPARC - arm-*-none ARM standalone systems - arm-*-linux Linux-2.x on ARM - arm-*-linuxaout Linux-2.x on ARM using a.out binaries - mips*-*-linux-gnu Linux-2.x on MIPS - ia64-*-linux-gnu Linux-2.x on ia64 - s390-*-linux-gnu Linux-2.x on IBM S/390 - s390x-*-linux-gnu Linux-2.x on IBM S/390 64-bit - cris-*-linux-gnu Linux-2.4+ on CRIS - -Ports to other Linux platforms are in development, and may in fact work -already, but no one has sent us success reports for them. Currently no -ports to other operating systems are underway, although a few people have -expressed interest. - -If you have a system not listed above (or in the `README' file) and you are -really interested in porting it, see the GNU C Library web pages to learn -how to start contributing: - - http://www.gnu.org/software/libc/resources.html - -??binsize What compiler do I need to build GNU libc? - -{UD} You must use GNU CC to compile GNU libc. A lot of extensions of GNU CC -are used to increase portability and speed. - -GNU CC is found, like all other GNU packages, on - - ftp://ftp.gnu.org/pub/gnu - -and the many mirror sites. ftp.gnu.org is always overloaded, so try to find -a local mirror first. - -You should always try to use the latest official release. Older versions -may not have all the features GNU libc requires. The current releases of -gcc (3.2 or newer) should work with the GNU C library (for MIPS see ?mips). - -Please note that gcc 2.95 and 2.95.x cannot compile glibc on Alpha due to -problems in the complex float support. - -?? When I try to compile glibc I get only error messages. - What's wrong? - -{UD} You definitely need GNU make to build GNU libc. No other make -program has the needed functionality. - -We recommend version GNU make version 3.79 or newer. Older versions have -bugs and/or are missing features. - -?? Do I need a special linker or assembler? - -{ZW} If you want a shared library, you need a linker and assembler that -understand all the features of ELF, including weak and versioned symbols. -The static library can be compiled with less featureful tools, but lacks key -features such as NSS. - -For Linux or Hurd, you want binutils 2.13 or higher. These are the only -versions we've tested and found reliable. Other versions may work but we -don't recommend them, especially not when C++ is involved. - -Other operating systems may come with system tools that have all the -necessary features, but this is moot because glibc hasn't been ported to -them. - -??powerpc Which compiler should I use for powerpc? - -{} Removed. Does not apply anymore. - -??arm Which tools should I use for ARM? - -{} Removed. Does not apply anymore. - -?? Do I need some more things to compile the GNU C Library? - -{UD} Yes, there are some more :-). - -* GNU gettext. This package contains the tools needed to construct - `message catalog' files containing translated versions of system - messages. See ftp://ftp.gnu.org/pub/gnu or better any mirror - site. (We distribute compiled message catalogs, but they may not be - updated in patches.) - -* Some files are built with special tools. E.g., files ending in .gperf - need a `gperf' program. The GNU version (now available in a separate - package, formerly only as part of libg++) is known to work while some - vendor versions do not. - - You should not need these tools unless you change the source files. - -* Perl 5 is needed if you wish to test an installation of GNU libc - as the primary C library. - -* When compiling for Linux, the header files of the Linux kernel must - be available to the compiler as <linux/*.h> and <asm/*.h>. - -* lots of disk space (~400MB for i?86-linux; more for RISC platforms). - -* plenty of time. Compiling just the shared and static libraries for - 35mins on a 2xPIII@550Mhz w/ 512MB RAM. On a 2xUltraSPARC-II@360Mhz - w/ 1GB RAM it takes about 14 minutes. Multiply this by 1.5 or 2.0 - if you build profiling and/or the highly optimized version as well. - For Hurd systems times are much higher. - - You should avoid compiling in a NFS mounted filesystem. This is - very slow. - - James Troup <J.J.Troup@comp.brad.ac.uk> reports a compile time for - an earlier (and smaller!) version of glibc of 45h34m for a full build - (shared, static, and profiled) on Atari Falcon (Motorola 68030 @ 16 Mhz, - 14 Mb memory) and Jan Barte <yann@plato.uni-paderborn.de> reports - 22h48m on Atari TT030 (Motorola 68030 @ 32 Mhz, 34 Mb memory) - - A full build of the PowerPC library took 1h on a PowerPC 750@400Mhz w/ - 64MB of RAM, and about 9h on a 601@60Mhz w/ 72Mb. - -?? What version of the Linux kernel headers should be used? - -{AJ,UD} The headers from the most recent Linux kernel should be used. The -headers used while compiling the GNU C library and the kernel binary used -when using the library do not need to match. The GNU C library runs without -problems on kernels that are older than the kernel headers used. The other -way round (compiling the GNU C library with old kernel headers and running -on a recent kernel) does not necessarily work. For example you can't use -new kernel features if you used old kernel headers to compile the GNU C -library. - -{ZW} Even if you are using a 2.0 kernel on your machine, we recommend you -compile GNU libc with 2.2 kernel headers. That way you won't have to -recompile libc if you ever upgrade to kernel 2.2. To tell libc which -headers to use, give configure the --with-headers switch -(e.g. --with-headers=/usr/src/linux-2.2.0/include). - -Note that you must configure the 2.2 kernel if you do this, otherwise libc -will be unable to find <linux/version.h>. Just change the current directory -to the root of the 2.2 tree and do `make include/linux/version.h'. - -?? The compiler hangs while building iconvdata modules. What's - wrong? - -{} Removed. Does not apply anymore. - -?? When I run `nm -u libc.so' on the produced library I still - find unresolved symbols. Can this be ok? - -{UD} Yes, this is ok. There can be several kinds of unresolved symbols: - -* magic symbols automatically generated by the linker. These have names - like __start_* and __stop_* - -* symbols starting with _dl_* come from the dynamic linker - -* weak symbols, which need not be resolved at all (fabs for example) - -Generally, you should make sure you find a real program which produces -errors while linking before deciding there is a problem. - -??addon What are these `add-ons'? - -{UD} To avoid complications with export rules or external source code some -optional parts of the libc are distributed as separate packages, e.g., the -linuxthreads package. - -To use these packages as part of GNU libc, just unpack the tarfiles in the -libc source directory and tell the configuration script about them using the ---enable-add-ons option. If you give just --enable-add-ons configure tries -to find all the add-on packages in your source tree. This may not work. If -it doesn't, or if you want to select only a subset of the add-ons, give a -comma-separated list of the add-ons to enable: - - configure --enable-add-ons=linuxthreads - -for example. - -Add-ons can add features (including entirely new shared libraries), override -files, provide support for additional architectures, and just about anything -else. The existing makefiles do most of the work; only some few stub rules -must be written to get everything running. - -Most add-ons are tightly coupled to a specific GNU libc version. Please -check that the add-ons work with the GNU libc. For example the linuxthreads -add-on has the same numbering scheme as the libc and will in general only -work with the corresponding libc. - -{AJ} With glibc 2.2 the crypt add-on and with glibc 2.1 the localedata -add-on have been integrated into the normal glibc distribution, crypt and -localedata are therefore not anymore add-ons. - -?? My XXX kernel emulates a floating-point coprocessor for me. - Should I enable --with-fp? - -{ZW} An emulated FPU is just as good as a real one, as far as the C library -is concerned. You only need to say --without-fp if your machine has no way -to execute floating-point instructions. - -People who are interested in squeezing the last drop of performance -out of their machine may wish to avoid the trap overhead, but this is -far more trouble than it's worth: you then have to compile -*everything* this way, including the compiler's internal libraries -(libgcc.a for GNU C), because the calling conventions change. - -?? When compiling GNU libc I get lots of errors saying functions - in glibc are duplicated in libgcc. - -{EY} This is *exactly* the same problem that I was having. The problem was -due to the fact that configure didn't correctly detect that the linker flag ---no-whole-archive was supported in my linker. In my case it was because I -had run ./configure with bogus CFLAGS, and the test failed. - -One thing that is particularly annoying about this problem is that once this -is misdetected, running configure again won't fix it unless you first delete -config.cache. - -{UD} Starting with glibc-2.0.3 there should be a better test to avoid some -problems of this kind. The setting of CFLAGS is checked at the very -beginning and if it is not usable `configure' will bark. - -?? Why do I get messages about missing thread functions when I use - librt? I don't even use threads. - -{UD} In this case you probably mixed up your installation. librt uses -threads internally and has implicit references to the thread library. -Normally these references are satisfied automatically but if the thread -library is not in the expected place you must tell the linker where it is. -When using GNU ld it works like this: - - gcc -o foo foo.c -Wl,-rpath-link=/some/other/dir -lrt - -The `/some/other/dir' should contain the thread library. `ld' will use the -given path to find the implicitly referenced library while not disturbing -any other link path. - -?? What's the problem with configure --enable-omitfp? - -{} Removed. Does not apply anymore. - -?? I get failures during `make check'. What should I do? - -{AJ} The testsuite should compile and run cleanly on your system; every -failure should be looked into. Depending on the failures, you probably -should not install the library at all. - -You should consider reporting it in bugzilla -<http://sourceware.org/bugzilla/> providing as much detail as possible. -If you run a test directly, please remember to set up the environment -correctly. You want to test the compiled library - and not your installed -one. The best way is to copy the exact command line which failed and run -the test from the subdirectory for this test in the sources. - -There are some failures which are not directly related to the GNU libc: -- Some compilers produce buggy code. No compiler gets single precision - complex numbers correct on Alpha. Otherwise, gcc-3.2 should be ok. -- The kernel might have bugs. For example on Linux/Alpha 2.0.34 the - floating point handling has quite a number of bugs and therefore most of - the test cases in the math subdirectory will fail. Linux 2.2 has - fixes for the floating point support on Alpha. The Linux/SPARC kernel has - also some bugs in the FPU emulation code (as of Linux 2.2.0). -- Other tools might have problems. For example bash 2.03 gives a - segmentation fault running the tst-rpmatch.sh test script. - -?? What is symbol versioning good for? Do I need it? - -{AJ} Symbol versioning solves problems that are related to interface -changes. One version of an interface might have been introduced in a -previous version of the GNU C library but the interface or the semantics of -the function has been changed in the meantime. For binary compatibility -with the old library, a newer library needs to still have the old interface -for old programs. On the other hand, new programs should use the new -interface. Symbol versioning is the solution for this problem. The GNU -libc version 2.1 uses symbol versioning by default if the installed binutils -supports it. - -We don't advise building without symbol versioning, since you lose binary -compatibility - forever! The binary compatibility you lose is not only -against the previous version of the GNU libc (version 2.0) but also against -all future versions. - -?? How can I compile on my fast ix86 machine a working libc for my slow - i386? After installing libc, programs abort with "Illegal - Instruction". - -{AJ} glibc and gcc might generate some instructions on your machine that -aren't available on i386. You've got to tell glibc that you're configuring -for i386 with adding i386 as your machine, for example: - - ../configure --prefix=/usr i386-pc-linux-gnu - -And you need to tell gcc to only generate i386 code, just add `-mcpu=i386' -(just -m386 doesn't work) to your CFLAGS. - -{UD} This applies not only to the i386. Compiling on a i686 for any older -model will also fail if the above methods are not used. - -?? `make' complains about a missing dlfcn/libdl.so when building - malloc/libmemprof.so. How can I fix this? - -{AJ} Older make version (<= 3.78.90) have a bug which was hidden by a bug in -glibc (<= 2.1.2). You need to upgrade make to a newer or fixed version. - -After upgrading make, you should remove the file sysd-sorted in your build -directory. The problem is that the broken make creates a wrong order for -one list in that file. The list has to be recreated with the new make - -which happens if you remove the file. - -You might encounter this bug also in other situations where make scans -directories. I strongly advise to upgrade your make version to 3.79 or -newer. - - -??mips Which tools should I use for MIPS? - -{AJ} You should use the current development version of gcc 3.2 or newer from -CVS. - -You need also recent binutils, anything before and including 2.11 will not -work correctly. Either try the Linux binutils 2.11.90.0.5 from HJ Lu or the -current development version of binutils from CVS. - -Please note that `make check' might fail for a number of the math tests -because of problems of the FPU emulation in the Linux kernel (the MIPS FPU -doesn't handle all cases and needs help from the kernel). - - -??powerpc64 Which compiler should I use for powerpc64? - -{SM} You want to use at least gcc 3.2 (together with the right versions -of all the other tools, of course). - -?? `make' fails when running rpcgen the first time, - what is going on? How do I fix this? - -{CO} The first invocation of rpcgen is also the first use of the recently -compiled dynamic loader. If there is any problem with the dynamic loader -it will more than likely fail to run rpcgen properly. This could be due to -any number of problems. - -The only real solution is to debug the loader and determine the problem -yourself. Please remember that for each architecture there may be various -patches required to get glibc HEAD into a runnable state. The best course -of action is to determine if you have all the required patches. - -?? Why do I get: - `#error "glibc cannot be compiled without optimization"', - when trying to compile GNU libc with GNU CC? - -{AJ,CO} There are a couple of reasons why the GNU C library will not work -correctly if it is not complied with optimzation. - -In the early startup of the dynamic loader (_dl_start), before -relocation of the PLT, you cannot make function calls. You must inline -the functions you will use during early startup, or call compiler -builtins (__builtin_*). - -Without optimizations enabled GNU CC will not inline functions. The -early startup of the dynamic loader will make function calls via an -unrelocated PLT and crash. - -Without auditing the dynamic linker code it would be difficult to remove -this requirement. - -Another reason is that nested functions must be inlined in many cases to -avoid executable stacks. - -In practice there is no reason to compile without optimizations, therefore -we require that GNU libc be compiled with optimizations enabled. - -? Installation and configuration issues - -?? Can I replace the libc on my Linux system with GNU libc? - -{UD} You cannot replace any existing libc for Linux with GNU libc. It is -binary incompatible and therefore has a different major version. You can, -however, install it alongside your existing libc. - -For Linux there are three major libc versions: - libc-4 a.out libc - libc-5 original ELF libc - libc-6 GNU libc - -You can have any combination of these three installed. For more information -consult documentation for shared library handling. The Makefiles of GNU -libc will automatically generate the needed symbolic links which the linker -will use. - -?? How do I configure GNU libc so that the essential libraries - like libc.so go into /lib and the other into /usr/lib? - -{UD,AJ} Like all other GNU packages GNU libc is designed to use a base -directory and install all files relative to this. The default is -/usr/local, because this is safe (it will not damage the system if installed -there). If you wish to install GNU libc as the primary C library on your -system, set the base directory to /usr (i.e. run configure --prefix=/usr -<other_options>). Note that this can damage your system; see ?safety for -details. - -Some systems like Linux have a filesystem standard which makes a difference -between essential libraries and others. Essential libraries are placed in -/lib because this directory is required to be located on the same disk -partition as /. The /usr subtree might be found on another -partition/disk. If you configure for Linux with --prefix=/usr, then this -will be done automatically. - -To install the essential libraries which come with GNU libc in /lib on -systems other than Linux one must explicitly request it. Autoconf has no -option for this so you have to use a `configparms' file (see the `INSTALL' -file for details). It should contain: - -slibdir=/lib -sysconfdir=/etc - -The first line specifies the directory for the essential libraries, the -second line the directory for system configuration files. - -??safety How should I avoid damaging my system when I install GNU libc? - -{ZW} If you wish to be cautious, do not configure with --prefix=/usr. If -you don't specify a prefix, glibc will be installed in /usr/local, where it -will probably not break anything. (If you wish to be certain, set the -prefix to something like /usr/local/glibc2 which is not used for anything.) - -The dangers when installing glibc in /usr are twofold: - -* glibc will overwrite the headers in /usr/include. Other C libraries - install a different but overlapping set of headers there, so the effect - will probably be that you can't compile anything. You need to rename - /usr/include out of the way before running `make install'. (Do not throw - it away; you will then lose the ability to compile programs against your - old libc.) - -* None of your old libraries, static or shared, can be used with a - different C library major version. For shared libraries this is not a - problem, because the filenames are different and the dynamic linker - will enforce the restriction. But static libraries have no version - information. You have to evacuate all the static libraries in - /usr/lib to a safe location. - -The situation is rather similar to the move from a.out to ELF which -long-time Linux users will remember. - -?? Do I need to use GNU CC to compile programs that will use the - GNU C Library? - -{ZW} In theory, no; the linker does not care, and the headers are supposed -to check for GNU CC before using its extensions to the C language. - -However, there are currently no ports of glibc to systems where another -compiler is the default, so no one has tested the headers extensively -against another compiler. You may therefore encounter difficulties. If you -do, please report them as bugs. - -Also, in several places GNU extensions provide large benefits in code -quality. For example, the library has hand-optimized, inline assembly -versions of some string functions. These can only be used with GCC. See -?string for details. - -??crypt When linking with the new libc I get unresolved symbols - `crypt' and `setkey'. Why aren't these functions in the - libc anymore? - - -{} Removed. Does not apply anymore. - -?? When I use GNU libc on my Linux system by linking against - the libc.so which comes with glibc all I get is a core dump. - -{UD} On Linux, gcc sets the dynamic linker to /lib/ld-linux.so.1 unless the -user specifies a --dynamic-linker argument. This is the name of the libc5 -dynamic linker, which does not work with glibc. - -For casual use of GNU libc you can just specify to the linker - --dynamic-linker=/lib/ld-linux.so.2 - -which is the glibc dynamic linker, on Linux systems. On other systems the -name is /lib/ld.so.1. When linking via gcc, you've got to add - -Wl,--dynamic-linker=/lib/ld-linux.so.2 - -to the gcc command line. - -To change your environment to use GNU libc for compiling you need to change -the `specs' file of your gcc. This file is normally found at - - /usr/lib/gcc-lib/<arch>/<version>/specs - -In this file you have to change a few things: - -- change `ld-linux.so.1' to `ld-linux.so.2' - -- remove all expression `%{...:-lgmon}'; there is no libgmon in glibc - -- fix a minor bug by changing %{pipe:-} to %| - -Here is what the gcc-2.7.2 specs file should look like when GNU libc is -installed at /usr: - ------------------------------------------------------------------------ -*asm: -%{V} %{v:%{!V:-V}} %{Qy:} %{!Qn:-Qy} %{n} %{T} %{Ym,*} %{Yd,*} %{Wa,*:%*} - -*asm_final: -%| - -*cpp: -%{fPIC:-D__PIC__ -D__pic__} %{fpic:-D__PIC__ -D__pic__} %{!m386:-D__i486__} %{posix:-D_POSIX_SOURCE} %{pthread:-D_REENTRANT} - -*cc1: -%{profile:-p} - -*cc1plus: - - -*endfile: -%{!shared:crtend.o%s} %{shared:crtendS.o%s} crtn.o%s - -*link: --m elf_i386 %{shared:-shared} %{!shared: %{!ibcs: %{!static: %{rdynamic:-export-dynamic} %{!dynamic-linker:-dynamic-linker /lib/ld-linux.so.2}} %{static:-static}}} - -*lib: -%{!shared: %{pthread:-lpthread} %{profile:-lc_p} %{!profile: -lc}} - -*libgcc: --lgcc - -*startfile: -%{!shared: %{pg:gcrt1.o%s} %{!pg:%{p:gcrt1.o%s} %{!p:%{profile:gcrt1.o%s} %{!profile:crt1.o%s}}}} crti.o%s %{!shared:crtbegin.o%s} %{shared:crtbeginS.o%s} - -*switches_need_spaces: - - -*signed_char: -%{funsigned-char:-D__CHAR_UNSIGNED__} - -*predefines: --D__ELF__ -Dunix -Di386 -Dlinux -Asystem(unix) -Asystem(posix) -Acpu(i386) -Amachine(i386) - -*cross_compile: -0 - -*multilib: -. ; - ------------------------------------------------------------------------ - -Things get a bit more complicated if you have GNU libc installed in some -other place than /usr, i.e., if you do not want to use it instead of the old -libc. In this case the needed startup files and libraries are not found in -the regular places. So the specs file must tell the compiler and linker -exactly what to use. - -Version 2.7.2.3 does and future versions of GCC will automatically -provide the correct specs. - -??nonsh Looking through the shared libc file I haven't found the - functions `stat', `lstat', `fstat', and `mknod' and while - linking on my Linux system I get error messages. How is - this supposed to work? - -{RM} Believe it or not, stat and lstat (and fstat, and mknod) are supposed -to be undefined references in libc.so.6! Your problem is probably a missing -or incorrect /usr/lib/libc.so file; note that this is a small text file now, -not a symlink to libc.so.6. It should look something like this: - -GROUP ( libc.so.6 libc_nonshared.a ) - -??excpt When I run an executable on one system which I compiled on - another, I get dynamic linker errors. Both systems have the same - version of glibc installed. What's wrong? - -{ZW} Glibc on one of these systems was compiled with gcc 2.7 or 2.8, the -other with egcs (any version). Egcs has functions in its internal -`libgcc.a' to support exception handling with C++. They are linked into -any program or dynamic library compiled with egcs, whether it needs them or -not. Dynamic libraries then turn around and export those functions again -unless special steps are taken to prevent them. - -When you link your program, it resolves its references to the exception -functions to the ones exported accidentally by libc.so. That works fine as -long as libc has those functions. On the other system, libc doesn't have -those functions because it was compiled by gcc 2.8, and you get undefined -symbol errors. The symbols in question are named things like -`__register_frame_info'. - -For glibc 2.0, the workaround is to not compile libc with egcs. We've also -incorporated a patch which should prevent the EH functions sneaking into -libc. It doesn't matter what compiler you use to compile your program. - -For glibc 2.1, we've chosen to do it the other way around: libc.so -explicitly provides the EH functions. This is to prevent other shared -libraries from doing it. - -{UD} Starting with glibc 2.1.1 you can compile glibc with gcc 2.8.1 or -newer since we have explicitly add references to the functions causing the -problem. But you nevertheless should use EGCS for other reasons -(see ?binsize). - -{GK} On some Linux distributions for PowerPC, you can see this when you have -built gcc or egcs from the Web sources (gcc versions 2.95 or earlier), then -re-built glibc. This happens because in these versions of gcc, exception -handling is implemented using an older method; the people making the -distributions are a little ahead of their time. - -A quick solution to this is to find the libgcc.a file that came with the -distribution (it would have been installed under /usr/lib/gcc-lib), do -`ar x libgcc.a frame.o' to get the frame.o file out, and add a line saying -`LDLIBS-c.so += frame.o' to the file `configparms' in the directory you're -building in. You can check you've got the right `frame.o' file by running -`nm frame.o' and checking that it has the symbols defined that you're -missing. - -This will let you build glibc with the C compiler. The C++ compiler -will still be binary incompatible with any C++ shared libraries that -you got with your distribution. - -?? How can I compile gcc 2.7.2.1 from the gcc source code using - glibc 2.x? - -{AJ} There's only correct support for glibc 2.0.x in gcc 2.7.2.3 or later. -But you should get at least gcc 2.95.3 (or later versions) anyway - -?? The `gencat' utility cannot process the catalog sources which - were used on my Linux libc5 based system. Why? - -{UD} The `gencat' utility provided with glibc complies to the XPG standard. -The older Linux version did not obey the standard, so they are not -compatible. - -To ease the transition from the Linux version some of the non-standard -features are also present in the `gencat' program of GNU libc. This mainly -includes the use of symbols for the message number and the automatic -generation of header files which contain the needed #defines to map the -symbols to integers. - -Here is a simple SED script to convert at least some Linux specific catalog -files to the XPG4 form: - ------------------------------------------------------------------------ -# Change catalog source in Linux specific format to standard XPG format. -# Ulrich Drepper <drepper@redhat.com>, 1996. -# -/^\$ #/ { - h - s/\$ #\([^ ]*\).*/\1/ - x - s/\$ #[^ ]* *\(.*\)/\$ \1/ -} - -/^# / { - s/^# \(.*\)/\1/ - G - s/\(.*\)\n\(.*\)/\2 \1/ -} ------------------------------------------------------------------------ - -?? Programs using libc have their messages translated, but other - behavior is not localized (e.g. collating order); why? - -{ZW} Translated messages are automatically installed, but the locale -database that controls other behaviors is not. You need to run localedef to -install this database, after you have run `make install'. For example, to -set up the French Canadian locale, simply issue the command - - localedef -i fr_CA -f ISO-8859-1 fr_CA - -Please see localedata/README in the source tree for further details. - -?? I have set up /etc/nis.conf, and the Linux libc 5 with NYS - works great. But the glibc NIS+ doesn't seem to work. - -{TK} The glibc NIS+ implementation uses a /var/nis/NIS_COLD_START file for -storing information about the NIS+ server and their public keys, because the -nis.conf file does not contain all the necessary information. You have to -copy a NIS_COLD_START file from a Solaris client (the NIS_COLD_START file is -byte order independent) or generate it with nisinit from the nis-tools -package; available at - - http://www.suse.de/~kukuk/linux/nisplus.html - -?? I have killed ypbind to stop using NIS, but glibc - continues using NIS. - -{TK} For faster NIS lookups, glibc uses the /var/yp/binding/ files from -ypbind. ypbind 3.3 and older versions don't always remove these files, so -glibc will continue to use them. Other BSD versions seem to work correctly. -Until ypbind 3.4 is released, you can find a patch at - - <ftp://ftp.kernel.org/pub/linux/utils/net/NIS/ypbind-3.3-glibc4.diff.gz> - -?? Under Linux/Alpha, I always get "do_ypcall: clnt_call: - RPC: Unable to receive; errno = Connection refused" when using NIS. - -{TK} You need a ypbind version which is 64bit clean. Some versions are not -64bit clean. A 64bit clean implementation is ypbind-mt. For ypbind 3.3, -you need the patch from ftp.kernel.org (See the previous question). I don't -know about other versions. - - -?? After installing glibc name resolving doesn't work properly. - -{AJ} You probably should read the manual section describing nsswitch.conf -(just type `info libc "NSS Configuration File"'). The NSS configuration -file is usually the culprit. - - -?? How do I create the databases for NSS? - -{AJ} If you have an entry "db" in /etc/nsswitch.conf you should also create -the database files. The glibc sources contain a Makefile which does the -necessary conversion and calls to create those files. The file is -`db-Makefile' in the subdirectory `nss' and you can call it with `make -f -db-Makefile'. Please note that not all services are capable of using a -database. Currently passwd, group, ethers, protocol, rpc, services shadow -and netgroup are implemented. See also ?nssdb. - -?? I have /usr/include/net and /usr/include/scsi as symlinks - into my Linux source tree. Is that wrong? - -{PB} This was necessary for libc5, but is not correct when using glibc. -Including the kernel header files directly in user programs usually does not -work (see ?kerhdr). glibc provides its own <net/*> and <scsi/*> header -files to replace them, and you may have to remove any symlink that you have -in place before you install glibc. However, /usr/include/asm and -/usr/include/linux should remain as they were. - -?? Programs like `logname', `top', `uptime' `users', `w' and - `who', show incorrect information about the (number of) - users on my system. Why? - -{MK} See ?getlog. - -?? After upgrading to glibc 2.1 with symbol versioning I get - errors about undefined symbols. What went wrong? - -{AJ} The problem is caused either by wrong program code or tools. In the -versioned libc a lot of symbols are now local that were global symbols in -previous versions. It seems that programs linked against older versions -often accidentally used libc global variables -- something that should not -happen. - -The only way to fix this is to recompile your program. Sorry, that's the -price you might have to pay once for quite a number of advantages with -symbol versioning. - -?? When I start the program XXX after upgrading the library - I get - XXX: Symbol `_sys_errlist' has different size in shared - object, consider re-linking - Why? What should I do? - -{UD} As the message says, relink the binary. The problem is that a few -symbols from the library can change in size and there is no way to avoid -this. _sys_errlist is a good example. Occasionally there are new error -numbers added to the kernel and this must be reflected at user level, -breaking programs that refer to them directly. - -Such symbols should normally not be used at all. There are mechanisms to -avoid using them. In the case of _sys_errlist, there is the strerror() -function which should _always_ be used instead. So the correct fix is to -rewrite that part of the application. - -In some situations (especially when testing a new library release) it might -be possible that a symbol changed size when that should not have happened. -So in case of doubt report such a warning message as a problem. - -?? What do I need for C++ development? - -{HJ,AJ} You need either egcs 1.1 which comes directly with libstdc++ or -gcc-2.8.1 together with libstdc++ 2.8.1.1. egcs 1.1 has the better C++ -support and works directly with glibc 2.1. If you use gcc-2.8.1 with -libstdc++ 2.8.1.1, you need to modify libstdc++ a bit. A patch is available -as: - <ftp://alpha.gnu.org/gnu/libstdc++-2.8.1.1-glibc2.1-diff.gz> - -Please note that libg++ 2.7.2 (and the Linux Versions 2.7.2.x) doesn't work -very well with the GNU C library due to vtable thunks. If you're upgrading -from glibc 2.0.x to 2.1 you have to recompile libstdc++ since the library -compiled for 2.0 is not compatible due to the new Large File Support (LFS) -in version 2.1. - -{UD} But since in the case of a shared libstdc++ the version numbers should -be different existing programs will continue to work. - -?? Even statically linked programs need some shared libraries - which is not acceptable for me. What can I do? - -{AJ} NSS (for details just type `info libc "Name Service Switch"') won't -work properly without shared libraries. NSS allows using different services -(e.g. NIS, files, db, hesiod) by just changing one configuration file -(/etc/nsswitch.conf) without relinking any programs. The only disadvantage -is that now static libraries need to access shared libraries. This is -handled transparently by the GNU C library. - -A solution is to configure glibc with --enable-static-nss. In this case you -can create a static binary that will use only the services dns and files -(change /etc/nsswitch.conf for this). You need to link explicitly against -all these services. For example: - - gcc -static test-netdb.c -o test-netdb \ - -Wl,--start-group -lc -lnss_files -lnss_dns -lresolv -Wl,--end-group - -The problem with this approach is that you've got to link every static -program that uses NSS routines with all those libraries. - -{UD} In fact, one cannot say anymore that a libc compiled with this -option is using NSS. There is no switch anymore. Therefore it is -*highly* recommended *not* to use --enable-static-nss since this makes -the behaviour of the programs on the system inconsistent. - -?? I just upgraded my Linux system to glibc and now I get - errors whenever I try to link any program. - -{ZW} This happens when you have installed glibc as the primary C library but -have stray symbolic links pointing at your old C library. If the first -`libc.so' the linker finds is libc 5, it will use that. Your program -expects to be linked with glibc, so the link fails. - -The most common case is that glibc put its `libc.so' in /usr/lib, but there -was a `libc.so' from libc 5 in /lib, which gets searched first. To fix the -problem, just delete /lib/libc.so. You may also need to delete other -symbolic links in /lib, such as /lib/libm.so if it points to libm.so.5. - -{AJ} The perl script test-installation.pl which is run as last step during -an installation of glibc that is configured with --prefix=/usr should help -detect these situations. If the script reports problems, something is -really screwed up. - -?? When I use nscd the machine freezes. - -{UD} You cannot use nscd with Linux 2.0.*. There is functionality missing -in the kernel and work-arounds are not suitable. Besides, some parts of the -kernel are too buggy when it comes to using threads. - -If you need nscd, you have to use at least a 2.1 kernel. - -Note that I have at this point no information about any other platform. - -?? I need lots of open files. What do I have to do? - -{AJ} This is at first a kernel issue. The kernel defines limits with -OPEN_MAX the number of simultaneous open files and with FD_SETSIZE the -number of used file descriptors. You need to change these values in your -kernel and recompile the kernel so that the kernel allows more open -files. You don't necessarily need to recompile the GNU C library since the -only place where OPEN_MAX and FD_SETSIZE is really needed in the library -itself is the size of fd_set which is used by select. - -The GNU C library is now select free. This means it internally has no -limits imposed by the `fd_set' type. Instead all places where the -functionality is needed the `poll' function is used. - -If you increase the number of file descriptors in the kernel you don't need -to recompile the C library. - -{UD} You can always get the maximum number of file descriptors a process is -allowed to have open at any time using - - number = sysconf (_SC_OPEN_MAX); - -This will work even if the kernel limits change. - -?? How do I get the same behavior on parsing /etc/passwd and - /etc/group as I have with libc5 ? - -{TK} The name switch setup in /etc/nsswitch.conf selected by most Linux -distributions does not support +/- and netgroup entries in the files like -/etc/passwd. Though this is the preferred setup some people might have -setups coming over from the libc5 days where it was the default to recognize -lines like this. To get back to the old behaviour one simply has to change -the rules for passwd, group, and shadow in the nsswitch.conf file as -follows: - -passwd: compat -group: compat -shadow: compat - -passwd_compat: nis -group_compat: nis -shadow_compat: nis - -??libs What needs to be recompiled when upgrading from glibc 2.0 to glibc - 2.1? - -{AJ,CG} If you just upgrade the glibc from 2.0.x (x <= 7) to 2.1, binaries -that have been linked against glibc 2.0 will continue to work. - -If you compile your own binaries against glibc 2.1, you also need to -recompile some other libraries. The problem is that libio had to be changed -and therefore libraries that are based or depend on the libio of glibc, -e.g. ncurses, slang and most C++ libraries, need to be recompiled. If you -experience strange segmentation faults in your programs linked against glibc -2.1, you might need to recompile your libraries. - -Another problem is that older binaries that were linked statically against -glibc 2.0 will reference the older nss modules (libnss_files.so.1 instead of -libnss_files.so.2), so don't remove them. Also, the old glibc-2.0 compiled -static libraries (libfoo.a) which happen to depend on the older libio -behavior will be broken by the glibc 2.1 upgrade. We plan to produce a -compatibility library that people will be able to link in if they want -to compile a static library generated against glibc 2.0 into a program -on a glibc 2.1 system. You just add -lcompat and you should be fine. - -The glibc-compat add-on will provide the libcompat.a library, the older -nss modules, and a few other files. Together, they should make it -possible to do development with old static libraries on a glibc 2.1 -system. This add-on is still in development. You can get it from - <ftp://alpha.gnu.org/gnu/glibc/glibc-compat-2.1.tar.gz> -but please keep in mind that it is experimental. - -?? Why is extracting files via tar so slow? - -{AJ} Extracting of tar archives might be quite slow since tar has to look up -userid and groupids and doesn't cache negative results. If you have nis or -nisplus in your /etc/nsswitch.conf for the passwd and/or group database, -each file extractions needs a network connection. There are two possible -solutions: - -- do you really need NIS/NIS+ (some Linux distributions add by default - nis/nisplus even if it's not needed)? If not, just remove the entries. - -- if you need NIS/NIS+, use the Name Service Cache Daemon nscd that comes - with glibc 2.1. - -?? Compiling programs I get parse errors in libio.h (e.g. "parse error - before `_IO_seekoff'"). How should I fix this? - -{AJ} You might get the following errors when upgrading to glibc 2.1: - - In file included from /usr/include/stdio.h:57, - from ... - /usr/include/libio.h:335: parse error before `_IO_seekoff' - /usr/include/libio.h:335: parse error before `_G_off64_t' - /usr/include/libio.h:336: parse error before `_IO_seekpos' - /usr/include/libio.h:336: parse error before `_G_fpos64_t' - -The problem is a wrong _G_config.h file in your include path. The -_G_config.h file that comes with glibc 2.1 should be used and not one from -libc5 or from a compiler directory. To check which _G_config.h file the -compiler uses, compile your program with `gcc -E ...|grep G_config.h' and -remove that file. Your compiler should pick up the file that has been -installed by glibc 2.1 in your include directory. - -?? After upgrading to glibc 2.1, libraries that were compiled against - glibc 2.0.x don't work anymore. - -{AJ} See ?libs. - -??nssdb What happened to the Berkeley DB libraries? Can I still use db - in /etc/nsswitch.conf? - -{AJ} Due to too many incompatible changes in disk layout and API of Berkeley -DB and a too tight coupling of libc and libdb, the db library has been -removed completely from glibc 2.2. The only place that really used the -Berkeley DB was the NSS db module. - -The NSS db module has been rewritten to support a number of different -versions of Berkeley DB for the NSS db module. Currently the releases 2.x -and 3.x of Berkeley DB are supported. The older db 1.85 library is not -supported. You can use the version from glibc 2.1.x or download a version -from Sleepycat Software (http://www.sleepycat.com). The library has to be -compiled as shared library and installed in the system lib directory -(normally /lib). The library needs to have a special soname to be found by -the NSS module. - -If public structures change in a new Berkeley db release, this needs to be -reflected in glibc. - -Currently the code searches for libraries with a soname of "libdb.so.3" -(that's the name from db 2.4.14 which comes with glibc 2.1.x) and -"libdb-3.0.so" (the name used by db 3.0.55 as default). - -The nss_db module is now in a separate package since it requires a database -library being available. - -?? What has do be done when upgrading to glibc 2.2? - -{AJ} The upgrade to glibc 2.2 should run smoothly, there's in general no -need to recompile programs or libraries. Nevertheless, some changes might -be needed after upgrading: -- The utmp daemon has been removed and is not supported by glibc anymore. - If it has been in use, it should be switched off. -- Programs using IPv6 have to be recompiled due to incompatible changes in - sockaddr_in6 by the IPv6 working group. -- The Berkeley db libraries have been removed (for details see ?nssdb). -- The format of the locale files has changed, all locales should be - regenerated with localedef. All statically linked applications which use - i18n should be recompiled, otherwise they'll not be localized. -- glibc comes with a number of new applications. For example ldconfig has - been implemented for glibc, the libc5 version of ldconfig is not needed - anymore. -- There's no more K&R compatibility in the glibc headers. The GNU C library - requires a C compiler that handles especially prototypes correctly. - Especially gcc -traditional will not work with glibc headers. - -Please read also the NEWS file which is the authoritative source for this -and gives more details for some topics. - -?? The makefiles want to do a CVS commit. - -{} Removed. Does not apply anymore. - -?? When compiling C++ programs, I get a compilation error in streambuf.h. - -{BH} You are using g++ 2.95.2? After upgrading to glibc 2.2, you need to -apply a patch to the include files in /usr/include/g++, because the fpos_t -type has changed in glibc 2.2. The patch is at - - http://www.haible.de/bruno/gccinclude-glibc-2.2-compat.diff - -?? When recompiling GCC, I get compilation errors in libio. - -{BH} You are trying to recompile gcc 2.95.2? Use gcc 2.95.3 instead. -This version is needed because the fpos_t type and a few libio internals -have changed in glibc 2.2, and gcc 2.95.3 contains a corresponding patch. - -?? Why shall glibc never get installed on GNU/Linux systems in -/usr/local? - -{AJ} The GNU C compiler treats /usr/local/include and /usr/local/lib in a -special way, these directories will be searched before the system -directories. Since on GNU/Linux the system directories /usr/include and -/usr/lib contain a --- possibly different --- version of glibc and mixing -certain files from different glibc installations is not supported and will -break, you risk breaking your complete system. If you want to test a glibc -installation, use another directory as argument to --prefix. If you like to -install this glibc version as default version, overriding the existing one, -use --prefix=/usr and everything will go in the right places. - -?? When recompiling GCC, I get compilation errors in libstdc++. - -{BH} You are trying to recompile gcc 3.2? You need to patch gcc 3.2, -because some last minute changes were made in glibc 2.3 which were not -known when gcc 3.2 was released. The patch is at - - http://www.haible.de/bruno/gcc-3.2-glibc-2.3-compat.diff - -? Source and binary incompatibilities, and what to do about them - -?? I expect GNU libc to be 100% source code compatible with - the old Linux based GNU libc. Why isn't it like this? - -{DMT,UD} Not every extension in Linux libc's history was well thought-out. -In fact it had a lot of problems with standards compliance and with -cleanliness. With the introduction of a new version number these errors can -now be corrected. Here is a list of the known source code -incompatibilities: - -* _GNU_SOURCE: glibc does not make the GNU extensions available - automatically. If a program depends on GNU extensions or some - other non-standard functionality, it is necessary to compile it - with the C compiler option -D_GNU_SOURCE, or better, to put - `#define _GNU_SOURCE' at the beginning of your source files, before - any C library header files are included. This difference normally - manifests itself in the form of missing prototypes and/or data type - definitions. Thus, if you get such errors, the first thing you - should do is try defining _GNU_SOURCE and see if that makes the - problem go away. - - For more information consult the file `NOTES' in the GNU C library - sources. - -* reboot(): GNU libc sanitizes the interface of reboot() to be more - compatible with the interface used on other OSes. reboot() as - implemented in glibc takes just one argument. This argument - corresponds to the third argument of the Linux reboot system call. - That is, a call of the form reboot(a, b, c) needs to be changed into - reboot(c). Beside this the header <sys/reboot.h> defines the needed - constants for the argument. These RB_* constants should be used - instead of the cryptic magic numbers. - -* swapon(): the interface of this function didn't change, but the - prototype is in a separate header file <sys/swap.h>. This header - file also provides the SWAP_* constants defined by <linux/swap.h>; - you should use them for the second argument to swapon(). - -* errno: If a program uses the variable "errno", then it _must_ - include <errno.h>. The old libc often (erroneously) declared this - variable implicitly as a side-effect of including other libc header - files. glibc is careful to avoid such namespace pollution, which, - in turn, means that you really need to include the header files that - you depend on. This difference normally manifests itself in the - form of the compiler complaining about references to an undeclared - symbol "errno". - -* Linux-specific syscalls: All Linux system calls now have appropriate - library wrappers and corresponding declarations in various header files. - This is because the syscall() macro that was traditionally used to - work around missing syscall wrappers are inherently non-portable and - error-prone. The following table lists all the new syscall stubs, - the header-file declaring their interface and the system call name. - - syscall name: wrapper name: declaring header file: - ------------- ------------- ---------------------- - bdflush bdflush <sys/kdaemon.h> - syslog ksyslog_ctl <sys/klog.h> - -* lpd: Older versions of lpd depend on a routine called _validuser(). - The library does not provide this function, but instead provides - __ivaliduser() which has a slightly different interface. Simply - upgrading to a newer lpd should fix this problem (e.g., the 4.4BSD - lpd is known to be working). - -* resolver functions/BIND: like on many other systems the functions of - the resolver library are not included in libc itself. There is a - separate library libresolv. If you get undefined symbol errors for - symbols starting with `res_*' simply add -lresolv to your linker - command line. - -* the `signal' function's behavior corresponds to the BSD semantic and - not the SysV semantic as it was in libc-5. The interface on all GNU - systems shall be the same and BSD is the semantic of choice. To use - the SysV behavior simply use `sysv_signal', or define _XOPEN_SOURCE. - See ?signal for details. - -??getlog Why does getlogin() always return NULL on my Linux box? - -{UD} The GNU C library has a format for the UTMP and WTMP file which differs -from what your system currently has. It was extended to fulfill the needs -of the next years when IPv6 is introduced. The record size is different and -some fields have different positions. The files written by functions from -the one library cannot be read by functions from the other library. Sorry, -but this is what a major release is for. It's better to have a cut now than -having no means to support the new techniques later. - -?? Where are the DST_* constants found in <sys/time.h> on many - systems? - -{UD} These constants come from the old BSD days and are not used anymore -(libc5 does not actually implement the handling although the constants are -defined). - -Instead GNU libc contains zone database support and compatibility code for -POSIX TZ environment variable handling. For former is very much preferred -(see ?tzdb). - -?? The prototypes for `connect', `accept', `getsockopt', - `setsockopt', `getsockname', `getpeername', `send', - `sendto', and `recvfrom' are different in GNU libc from - any other system I saw. This is a bug, isn't it? - -{UD} No, this is no bug. This version of GNU libc already follows the new -Single Unix specifications (and I think the POSIX.1g draft which adopted the -solution). The type for a parameter describing a size is now `socklen_t', a -new type. - -??kerhdr On Linux I've got problems with the declarations in Linux - kernel headers. - -{UD,AJ} On Linux, the use of kernel headers is reduced to the minimum. This -gives Linus the ability to change the headers more freely. Also, user -programs are now insulated from changes in the size of kernel data -structures. - -For example, the sigset_t type is 32 or 64 bits wide in the kernel. In -glibc it is 1024 bits wide. This guarantees that when the kernel gets a -bigger sigset_t (for POSIX.1e realtime support, say) user programs will not -have to be recompiled. Consult the header files for more information about -the changes. - -Therefore you shouldn't include Linux kernel header files directly if glibc -has defined a replacement. Otherwise you might get undefined results because -of type conflicts. - -?? I don't include any kernel headers myself but the compiler - still complains about redeclarations of types in the kernel - headers. - -{UD} The kernel headers before Linux 2.1.61 and 2.0.32 don't work correctly -with glibc. Compiling C programs is possible in most cases but C++ programs -have (due to the change of the name lookups for `struct's) problems. One -prominent example is `struct fd_set'. - -There might be some problems left but 2.1.61/2.0.32 fix most of the known -ones. See the BUGS file for other known problems. - -??signal Why don't signals interrupt system calls anymore? - -{ZW} By default GNU libc uses the BSD semantics for signal(), unlike Linux -libc 5 which used System V semantics. This is partially for compatibility -with other systems and partially because the BSD semantics tend to make -programming with signals easier. - -There are three differences: - -* BSD-style signals that occur in the middle of a system call do not - affect the system call; System V signals cause the system call to - fail and set errno to EINTR. - -* BSD signal handlers remain installed once triggered. System V signal - handlers work only once, so one must reinstall them each time. - -* A BSD signal is blocked during the execution of its handler. In other - words, a handler for SIGCHLD (for example) does not need to worry about - being interrupted by another SIGCHLD. It may, however, be interrupted - by other signals. - -There is general consensus that for `casual' programming with signals, the -BSD semantics are preferable. You don't need to worry about system calls -returning EINTR, and you don't need to worry about the race conditions -associated with one-shot signal handlers. - -If you are porting an old program that relies on the old semantics, you can -quickly fix the problem by changing signal() to sysv_signal() throughout. -Alternatively, define _XOPEN_SOURCE before including <signal.h>. - -For new programs, the sigaction() function allows you to specify precisely -how you want your signals to behave. All three differences listed above are -individually switchable on a per-signal basis with this function. - -If all you want is for one specific signal to cause system calls to fail and -return EINTR (for example, to implement a timeout) you can do this with -siginterrupt(). - - -??string I've got errors compiling code that uses certain string - functions. Why? - -{AJ} glibc 2.1 has special string functions that are faster than the normal -library functions. Some of the functions are additionally implemented as -inline functions and others as macros. This might lead to problems with -existing codes but it is explicitly allowed by ISO C. - -The optimized string functions are only used when compiling with -optimizations (-O1 or higher). The behavior can be changed with two feature -macros: - -* __NO_STRING_INLINES: Don't do any string optimizations. -* __USE_STRING_INLINES: Use assembly language inline functions (might - increase code size dramatically). - -Since some of these string functions are now additionally defined as macros, -code like "char *strncpy();" doesn't work anymore (and is unnecessary, since -<string.h> has the necessary declarations). Either change your code or -define __NO_STRING_INLINES. - -{UD} Another problem in this area is that gcc still has problems on machines -with very few registers (e.g., ix86). The inline assembler code can require -almost all the registers and the register allocator cannot always handle -this situation. - -One can disable the string optimizations selectively. Instead of writing - - cp = strcpy (foo, "lkj"); - -one can write - - cp = (strcpy) (foo, "lkj"); - -This disables the optimization for that specific call. - -?? I get compiler messages "Initializer element not constant" with - stdin/stdout/stderr. Why? - -{RM,AJ} Constructs like: - static FILE *InPtr = stdin; - -lead to this message. This is correct behaviour with glibc since stdin is -not a constant expression. Please note that a strict reading of ISO C does -not allow above constructs. - -One of the advantages of this is that you can assign to stdin, stdout, and -stderr just like any other global variable (e.g. `stdout = my_stream;'), -which can be very useful with custom streams that you can write with libio -(but beware this is not necessarily portable). The reason to implement it -this way were versioning problems with the size of the FILE structure. - -To fix those programs you've got to initialize the variable at run time. -This can be done, e.g. in main, like: - - static FILE *InPtr; - int main(void) - { - InPtr = stdin; - } - -or by constructors (beware this is gcc specific): - - static FILE *InPtr; - static void inPtr_construct (void) __attribute__((constructor)); - static void inPtr_construct (void) { InPtr = stdin; } - - -?? I can't compile with gcc -traditional (or - -traditional-cpp). Why? - -{AJ} glibc2 does break -traditional and -traditonal-cpp - and will continue -to do so. For example constructs of the form: - - enum {foo - #define foo foo - } - -are useful for debugging purposes (you can use foo with your debugger that's -why we need the enum) and for compatibility (other systems use defines and -check with #ifdef). - -?? I get some errors with `gcc -ansi'. Isn't glibc ANSI compatible? - -{AJ} The GNU C library is compatible with the ANSI/ISO C standard. If -you're using `gcc -ansi', the glibc includes which are specified in the -standard follow the standard. The ANSI/ISO C standard defines what has to be -in the include files - and also states that nothing else should be in the -include files (btw. you can still enable additional standards with feature -flags). - -The GNU C library is conforming to ANSI/ISO C - if and only if you're only -using the headers and library functions defined in the standard. - -?? I can't access some functions anymore. nm shows that they do - exist but linking fails nevertheless. - -{AJ} With the introduction of versioning in glibc 2.1 it is possible to -export only those identifiers (functions, variables) that are really needed -by application programs and by other parts of glibc. This way a lot of -internal interfaces are now hidden. nm will still show those identifiers -but marking them as internal. ISO C states that identifiers beginning with -an underscore are internal to the libc. An application program normally -shouldn't use those internal interfaces (there are exceptions, -e.g. __ivaliduser). If a program uses these interfaces, it's broken. These -internal interfaces might change between glibc releases or dropped -completely. - -?? When using the db-2 library which comes with glibc is used in - the Perl db modules the testsuite is not passed. This did not - happen with db-1, gdbm, or ndbm. - -{} Removed. Does not apply anymore. - -?? The pow() inline function I get when including <math.h> is broken. - I get segmentation faults when I run the program. - -{UD} Nope, the implementation is correct. The problem is with egcs version -prior to 1.1. I.e., egcs 1.0 to 1.0.3 are all broken (at least on Intel). -If you have to use this compiler you must define __NO_MATH_INLINES before -including <math.h> to prevent the inline functions from being used. egcs 1.1 -fixes the problem. I don't know about gcc 2.8 and 2.8.1. - -?? The sys/sem.h file lacks the definition of `union semun'. - -{UD} Nope. This union has to be provided by the user program. Former glibc -versions defined this but it was an error since it does not make much sense -when thinking about it. The standards describing the System V IPC functions -define it this way and therefore programs must be adopted. - -?? Why has <netinet/ip_fw.h> disappeared? - -{AJ} The corresponding Linux kernel data structures and constants are -totally different in Linux 2.0 and Linux 2.2. This situation has to be -taken care in user programs using the firewall structures and therefore -those programs (ipfw is AFAIK the only one) should deal with this problem -themselves. - -?? I get floods of warnings when I use -Wconversion and include - <string.h> or <math.h>. - -{ZW} <string.h> and <math.h> intentionally use prototypes to override -argument promotion. -Wconversion warns about all these. You can safely -ignore the warnings. - --Wconversion isn't really intended for production use, only for shakedown -compiles after converting an old program to standard C. - - -?? After upgrading to glibc 2.1, I receive errors about - unresolved symbols, like `_dl_initial_searchlist' and can not - execute any binaries. What went wrong? - -{AJ} This normally happens if your libc and ld (dynamic linker) are from -different releases of glibc. For example, the dynamic linker -/lib/ld-linux.so.2 comes from glibc 2.0.x, but the version of libc.so.6 is -from glibc 2.1. - -The path /lib/ld-linux.so.2 is hardcoded in every glibc2 binary but -libc.so.6 is searched via /etc/ld.so.cache and in some special directories -like /lib and /usr/lib. If you run configure with another prefix than /usr -and put this prefix before /lib in /etc/ld.so.conf, your system will break. - -So what can you do? Either of the following should work: - -* Run `configure' with the same prefix argument you've used for glibc 2.0.x - so that the same paths are used. -* Replace /lib/ld-linux.so.2 with a link to the dynamic linker from glibc - 2.1. - -You can even call the dynamic linker by hand if everything fails. You've -got to set LD_LIBRARY_PATH so that the corresponding libc is found and also -need to provide an absolute path to your binary: - - LD_LIBRARY_PATH=<path-where-libc.so.6-lives> \ - <path-where-corresponding-dynamic-linker-lives>/ld-linux.so.2 \ - <path-to-binary>/binary - -For example `LD_LIBRARY_PATH=/libold /libold/ld-linux.so.2 /bin/mv ...' -might be useful in fixing a broken system (if /libold contains dynamic -linker and corresponding libc). - -With that command line no path is used. To further debug problems with the -dynamic linker, use the LD_DEBUG environment variable, e.g. -`LD_DEBUG=help echo' for the help text. - -If you just want to test this release, don't put the lib directory in -/etc/ld.so.conf. You can call programs directly with full paths (as above). -When compiling new programs against glibc 2.1, you've got to specify the -correct paths to the compiler (option -I with gcc) and linker (options ---dynamic-linker, -L and --rpath). - -?? bonnie reports that char i/o with glibc 2 is much slower than with - libc5. What can be done? - -{AJ} The GNU C library uses thread safe functions by default and libc5 used -non thread safe versions. The non thread safe functions have in glibc the -suffix `_unlocked', for details check <stdio.h>. Using `putc_unlocked' etc. -instead of `putc' should give nearly the same speed with bonnie (bonnie is a -benchmark program for measuring disk access). - -?? Programs compiled with glibc 2.1 can't read db files made with glibc - 2.0. What has changed that programs like rpm break? - -{} Removed. Does not apply anymore. - -?? Autoconf's AC_CHECK_FUNC macro reports that a function exists, but - when I try to use it, it always returns -1 and sets errno to ENOSYS. - -{ZW} You are using a 2.0 Linux kernel, and the function you are trying to -use is only implemented in 2.1/2.2. Libc considers this to be a function -which exists, because if you upgrade to a 2.2 kernel, it will work. One -such function is sigaltstack. - -Your program should check at runtime whether the function works, and -implement a fallback. Note that Autoconf cannot detect unimplemented -functions in other systems' C libraries, so you need to do this anyway. - -?? My program segfaults when I call fclose() on the FILE* returned - from setmntent(). Is this a glibc bug? - -{GK} No. Don't do this. Use endmntent(), that's what it's for. - -In general, you should use the correct deallocation routine. For instance, -if you open a file using fopen(), you should deallocate the FILE * using -fclose(), not free(), even though the FILE * is also a pointer. - -In the case of setmntent(), it may appear to work in most cases, but it -won't always work. Unfortunately, for compatibility reasons, we can't -change the return type of setmntent() to something other than FILE *. - -?? I get "undefined reference to `atexit'" - -{UD} This means that your installation is somehow broken. The situation is -the same as for 'stat', 'fstat', etc (see ?nonsh). Investigate why the -linker does not pick up libc_nonshared.a. - -If a similar message is issued at runtime this means that the application or -DSO is not linked against libc. This can cause problems since 'atexit' is -not exported anymore. - - -? Miscellaneous - -?? After I changed configure.in I get `Autoconf version X.Y. - or higher is required for this script'. What can I do? - -{UD} You have to get the specified autoconf version (or a later one) -from your favorite mirror of ftp.gnu.org. - -?? When I try to compile code which uses IPv6 headers and - definitions on my Linux 2.x.y system I am in trouble. - Nothing seems to work. - -{UD} The problem is that IPv6 development still has not reached a point -where the headers are stable. There are still lots of incompatible changes -made and the libc headers have to follow. - -{PB} The 2.1 release of GNU libc aims to comply with the current versions of -all the relevant standards. The IPv6 support libraries for older Linux -systems used a different naming convention and so code written to work with -them may need to be modified. If the standards make incompatible changes in -the future then the libc may need to change again. - -IPv6 will not work with a 2.0.x kernel. When kernel 2.2 is released it -should contain all the necessary support; until then you should use the -latest 2.1.x release you can find. As of 98/11/26 the currently recommended -kernel for IPv6 is 2.1.129. - -Also, as of the 2.1 release the IPv6 API provided by GNU libc is not -100% complete. - -??tzdb When I set the timezone by setting the TZ environment variable - to EST5EDT things go wrong since glibc computes the wrong time - from this information. - -{UD} The problem is that people still use the braindamaged POSIX method to -select the timezone using the TZ environment variable with a format EST5EDT -or whatever. People, if you insist on using TZ instead of the timezone -database (see below), read the POSIX standard, the implemented behaviour is -correct! What you see is in fact the result of the decisions made while -POSIX.1 was created. We've only implemented the handling of TZ this way to -be POSIX compliant. It is not really meant to be used. - -The alternative approach to handle timezones which is implemented is the -correct one to use: use the timezone database. This avoids all the problems -the POSIX method has plus it is much easier to use. Simply run the tzselect -shell script, answer the question and use the name printed in the end by -making a symlink /etc/localtime pointing to /usr/share/zoneinfo/NAME (NAME -is the returned value from tzselect). That's all. You never again have to -worry. - -So, please avoid sending bug reports about time related problems if you use -the POSIX method and you have not verified something is really broken by -reading the POSIX standards. - -?? What other sources of documentation about glibc are available? - -{AJ} The FSF has a page about the GNU C library at -<http://www.gnu.org/software/libc/>. The problem data base of open and -solved bugs in GNU libc is available at -<http://www-gnats.gnu.org:8080/cgi-bin/wwwgnats.pl>. Eric Green has written -a HowTo for converting from Linux libc5 to glibc2. The HowTo is accessible -via the FSF page and at <http://www.imaxx.net/~thrytis/glibc>. Frodo -Looijaard describes a different way installing glibc2 as secondary libc at -<http://huizen.dds.nl/~frodol/glibc>. - -Please note that this is not a complete list. - -?? The timezone string for Sydney/Australia is wrong since even when - daylight saving time is in effect the timezone string is EST. - -{UD} The problem for some timezones is that the local authorities decided -to use the term "summer time" instead of "daylight saving time". In this -case the abbreviation character `S' is the same as the standard one. So, -for Sydney we have - - Eastern Standard Time = EST - Eastern Summer Time = EST - -Great! To get this bug fixed convince the authorities to change the laws -and regulations of the country this effects. glibc behaves correctly. - -??make I've build make 3.77 against glibc 2.1 and now make gets - segmentation faults. - -{} Removed. Does not apply anymore, use make 3.79 or newer. - -?? Why do so many programs using math functions fail on my AlphaStation? - -{AO} The functions floor() and floorf() use an instruction that is not -implemented in some old PALcodes of AlphaStations. This may cause -`Illegal Instruction' core dumps or endless loops in programs that -catch these signals. Updating the firmware to a 1999 release has -fixed the problem on an AlphaStation 200 4/166. - -?? The conversion table for character set XX does not match with -what I expect. - -{UD} I don't doubt for a minute that some of the conversion tables contain -errors. We tried the best we can and relied on automatic generation of the -data to prevent human-introduced errors but this still is no guarantee. If -you think you found a problem please send a bug report describing it and -give an authoritive reference. The latter is important since otherwise -the current behaviour is as good as the proposed one. - -Before doing this look through the list of known problem first: - -- the GBK (simplified Chinese) encoding is based on Unicode tables. This - is good. These tables, however, differ slightly from the tables used - by the M$ people. The differences are these [+ Unicode, - M$]: - - +0xA1AA 0x2015 - +0xA844 0x2014 - -0xA1AA 0x2014 - -0xA844 0x2015 - - In addition the Unicode tables contain mappings for the GBK characters - 0xA8BC, 0xA8BF, 0xA989 to 0xA995, and 0xFE50 to 0xFEA0. - -- when mapping from EUC-CN to GBK and vice versa we ignore the fact that - the coded character at position 0xA1A4 maps to different Unicode - characters. Since the iconv() implementation can do whatever it wants - if it cannot directly map a character this is a perfectly good solution - since the semantics and appearance of the character does not change. - -?? How can I find out which version of glibc I am using in the moment? - -{UD} If you want to find out about the version from the command line simply -run the libc binary. This is probably not possible on all platforms but -where it is simply locate the libc DSO and start it as an application. On -Linux like - - /lib/libc.so.6 - -This will produce all the information you need. - -What always will work is to use the API glibc provides. Compile and run the -following little program to get the version information: - -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -#include <stdio.h> -#include <gnu/libc-version.h> -int main (void) { puts (gnu_get_libc_version ()); return 0; } -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ - -This interface can also obviously be used to perform tests at runtime if -this should be necessary. - -?? Context switching with setcontext() does not work from within - signal handlers. - -{DMT} The Linux implementations (IA-64, S390 so far) of setcontext() -supports synchronous context switches only. There are several reasons for -this: - -- UNIX provides no other (portable) way of effecting a synchronous - context switch (also known as co-routine switch). Some versions - support this via setjmp()/longjmp() but this does not work - universally. - -- As defined by the UNIX '98 standard, the only way setcontext() - could trigger an asychronous context switch is if this function - were invoked on the ucontext_t pointer passed as the third argument - to a signal handler. But according to draft 5, XPG6, XBD 2.4.3, - setcontext() is not among the set of routines that may be called - from a signal handler. - -- If setcontext() were to be used for asynchronous context switches, - all kinds of synchronization and re-entrancy issues could arise and - these problems have already been solved by real multi-threading - libraries (e.g., POSIX threads or Linux threads). - -- Synchronous context switching can be implemented entirely in - user-level and less state needs to be saved/restored than for an - asynchronous context switch. It is therefore useful to distinguish - between the two types of context switches. Indeed, some - application vendors are known to use setcontext() to implement - co-routines on top of normal (heavier-weight) pre-emptable threads. - -It should be noted that if someone was dead-bent on using setcontext() -on the third arg of a signal handler, then IA-64 Linux could support -this via a special version of sigaction() which arranges that all -signal handlers start executing in a shim function which takes care of -saving the preserved registers before calling the real signal handler -and restoring them afterwards. In other words, we could provide a -compatibility layer which would support setcontext() for asynchronous -context switches. However, given the arguments above, I don't think -that makes sense. setcontext() provides a decent co-routine interface -and we should just discourage any asynchronous use (which just calls -for trouble at any rate). - - - -Answers were given by: -{UD} Ulrich Drepper, <drepper@redhat.com> -{DMT} David Mosberger-Tang, <davidm@hpl.hp.com> -{RM} Roland McGrath, <roland@gnu.org> -{AJ} Andreas Jaeger, <aj@suse.de> -{EY} Eric Youngdale, <eric@andante.jic.com> -{PB} Phil Blundell, <Philip.Blundell@pobox.com> -{MK} Mark Kettenis, <kettenis@phys.uva.nl> -{ZW} Zack Weinberg, <zack@rabi.phys.columbia.edu> -{TK} Thorsten Kukuk, <kukuk@suse.de> -{GK} Geoffrey Keating, <geoffk@redhat.com> -{HJ} H.J. Lu, <hjl@gnu.org> -{CG} Cristian Gafton, <gafton@redhat.com> -{AO} Alexandre Oliva, <aoliva@redhat.com> -{BH} Bruno Haible, <haible@clisp.cons.org> -{SM} Steven Munroe, <sjmunroe@us.ibm.com> -{CO} Carlos O'Donell, <carlos@systemhalted.org> - -Local Variables: - mode:outline - outline-regexp:"\\?" - fill-column:76 -End: @@ -363,7 +363,7 @@ TAGS: generated := $(generated) stubs.h -files-for-dist := README FAQ INSTALL configure ChangeLog NEWS +files-for-dist := README INSTALL configure ChangeLog NEWS # Regenerate stuff, then error if these things are not committed yet. dist-prepare: $(files-for-dist) @@ -400,8 +400,6 @@ endef INSTALL: manual/install.texi manual/macros.texi; $(format-me) manual/dir-add.texi manual/dir-add.info: FORCE $(MAKE) $(PARALLELMFLAGS) -C $(@D) $(@F) -FAQ: scripts/gen-FAQ.pl FAQ.in - $(PERL) $^ > $@.new && rm -f $@ && mv $@.new $@ && chmod a-w $@ FORCE: iconvdata/% localedata/% po/% manual/%: FORCE diff --git a/manual/install.texi b/manual/install.texi index 222ab3d..d2663f3 100644 --- a/manual/install.texi +++ b/manual/install.texi @@ -7,10 +7,10 @@ @c %MENU% How to install the GNU C Library @appendix Installing @theglibc{} -Before you do anything else, you should read the file @file{FAQ} located -at the top level of the source tree. This file answers common questions -and describes problems you may experience with compilation and -installation. It is updated more frequently than this manual. +Before you do anything else, you should read the FAQ at +@url{http://sourceware.org/glibc/wiki/FAQ}. It answers common +questions and describes problems you may experience with compilation +and installation. Features can be added to @theglibc{} via @dfn{add-on} bundles. These are separate tar files, which you unpack into the top level of the source diff --git a/scripts/gen-FAQ.pl b/scripts/gen-FAQ.pl deleted file mode 100755 index 9503903..0000000 --- a/scripts/gen-FAQ.pl +++ /dev/null @@ -1,144 +0,0 @@ -#! /usr/bin/perl - -=pod -This is a silly little program for generating the libc FAQ. - -The input format is: -top boilerplate -^L -? section name (one line) -?? question... -... -{ID} answer... -... -^L -{ID} name <email@address> -... - -which gets mapped to: - -top boilerplate -^L -1. section 1... -1.1. q1.1 -1.2. q1.2 -... -^L -1. section 1... - -1.1. q1.1 - -answer 1.1.... - - -^L -Answers were provided by: -... - -=cut - -# We slurp the whole file into a pair of assoc arrays indexed by -# the 'section.question' number. -%questions = (); -%answers = (); -$question = 0; - -# These arrays and counter keep track of the sections. -@sectcount = (); -@sections = (); -$section = 0; - -# Cross reference list. -%refs = (); - -# Separators. -$sepmaj = "\f\n" . ('~ ' x 36) . "\n\n"; -$sepmin = "\f\n" . ('. ' x 36) . "\n\n"; - -# Pass through the top boilerplate. -while(<>) -{ - last if $_ eq "\f\n"; - print; -} - -# Now the body. -while(<>) -{ - /\f/ && do - { - $sectcount[$section] = $question; - last; - }; - - s/^\?\s+// && do - { - chomp; - $sectcount[$section] = $question if $section > 0; - $section++; - $sections[$section] = $_; - $question = 0; - next; - }; - s/^\?\?(\w*?)\s+// && do - { - $cur = \%questions; - $question++; - $questions{$section,$question} = $_; - $refs{$1} = "$section.$question" if $1 ne ""; - next; - }; - /^\{/ && do - { - $cur = \%answers; - $answers{$section,$question} .= $_; - next; - }; - - ${$cur}{$section,$question} .= $_; -} - -# Now we have to clean up the newlines and deal with cross references. -foreach(keys %questions) { $questions{$_} =~ s/\n+$//; } -foreach(keys %answers) -{ - $answers{$_} =~ s/\n+$//; - $answers{$_} =~ s/(\s)\?(\w+)\b/$1 . "question " . ($refs{$2} or badref($2,$_), "!!$2")/eg; -} - -# Now output the formatted FAQ. -print $sepmaj; -for($i = 1; $i <= $section; $i++) -{ - print "$i. $sections[$i]\n\n"; - for($j = 1; $j <= $sectcount[$i]; $j++) - { - print "$i.$j.\t$questions{$i,$j}\n"; - } - print "\n"; -} - -print $sepmaj; -for($i = 1; $i <= $section; $i++) -{ - print "$i. $sections[$i]\n\n"; - for($j = 1; $j <= $sectcount[$i]; $j++) - { - print "$i.$j.\t$questions{$i,$j}\n\n"; - print $answers{$i,$j}, "\n\n"; - print "\n" if $j < $sectcount[$i]; - } - print $sepmin if $i < $section; -} - -print $sepmaj; - -# Pass through the trailer. -while(<>) { print; } - -sub badref -{ - my($ref,$quest) = @_; - $quest =~ s/$;/./; - print STDERR "Undefined reference to $ref in answer to Q$quest\n"; -} |