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Diffstat (limited to 'FAQ')
| -rw-r--r-- | FAQ | 78 |
1 files changed, 78 insertions, 0 deletions
@@ -19,6 +19,28 @@ this document let me know. ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ [Q1] ``What systems the GNU C Library runs on?'' +[Q2] ``What compiler do I need to translate GNU libc?'' + +[Q3] ``When starting make I get only errors messages. + What's wrong?'' + +[Q4] ``After I changed configure.in I get `Autoconf version X.Y. + or higher is required for this script'. What can I do?'' + +[Q5] ``Do I need a special linker or archiver?'' + +[Q6] ``Do I need some more things to compile GNU C Library?'' + +[Q7] ``When I run `nm libc.so|grep " U "' on the produced library + I still find unresolved symbols? Can this be ok?'' + +[Q8] ``I expect GNU libc to be 100% source code compatible with + the old Linux based GNU libc. Why isn't it like this?'' + + +~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ +[Q1] ``What systems the GNU C Library runs on?'' + [A1] {UD} This is difficult to answer. The file `README' lists the architectures GNU libc is known to run *at some time*. This does not mean that it still can be compiled and run on them in the moment. @@ -128,11 +150,67 @@ errors while linking. ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ +[Q8] ``I expect GNU libc to be 100% source code compatible with + the old Linux based GNU libc. Why isn't it like this?'' + +[A8] {DMT} Not every extension in Linux libc's history was well +thought. In fact it had a lot of problems with standard compliance +and cleanliness. With the introduction of a new version number these +errors now can be corrected. The following list shows a list of the +know source code incompatibilities. + +* _GNU_SOURCE: glibc does not automatically define _GNU_SOURCE. Thus, + if a program depends on GNU extensions, it is necessary + to compile it with C compiler option -D_GNU_SOURCE. This difference + normally mainfests 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 grep the header files in /usr/include and /usr/include/sys + to check whether the functions are really missing or whether it is + just necessary to add a define of _GNU_SOURCE. Similar comments apply + to _BSD_SOURCE, _POSIX_SOURCE, _SVID_SOURCE etc (see + /usr/include/features.h). + +* reboot(): GNU libc sanitizes the interface of reboot() to be more + compatible with the interface used on other OSes. In particular, + 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). + +* errno: If a program uses variable "errno", then it _must_ include header + file <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 the references of the 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 tables 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 <unistd.h> + create_module create_module <sys/module.h> + delete_module delete_module <sys/module.h> + get_kernel_syms get_kernel_syms <sys/module.h> + init_module init_module <sys/module.h> + syslog ksyslog_ctl <unistd.h> + + To get the Linux-specific declarations in <unistd.h>, you'll need + to define C pre-processor macro _LINUX_SOURCE during compilation. +~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ + Answers were given by: {UD} Ulrich Drepper, <drepper@cygnus.com> +{DMT} David Mosberger-Tang, <davidm@AZStarNet.com> Local Variables: |