diff options
Diffstat (limited to 'FAQ')
| -rw-r--r-- | FAQ | 43 |
1 files changed, 42 insertions, 1 deletions
@@ -113,6 +113,9 @@ please let me know. [Q31] ``What's the problem with configure --enable-omitfp?'' [Q32] ``Why don't signals interrupt system calls anymore?'' + +[Q33] ``I've got errors compiling code that uses certain string + functions. Why?'' ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ [Q1] ``What systems does the GNU C Library run on?'' @@ -812,7 +815,7 @@ happen. So in case of doubt report such a warning message as a problem. ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ [Q31] ``What's the problem with configure --enable-omitfp?'' -{AJ} When configuring with --enable-omitfp the libraries are build +[A31] {AJ} When configuring with --enable-omitfp the libraries are build without frame pointers. Some compilers produce in this situation buggy code and therefore we don't advise using it at the moment. @@ -870,6 +873,44 @@ siginterrupt(). ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ +[Q33] ``I've got errors compiling code that uses certain string + functions. Why?'' + +[A33] {AJ} glibc 2.1 has the much asked for optimized string +functions that are faster than the normal library functions. Some of +the functions are implemented as inline functions and others as +macros. +The optimized string functions are only used when compiling with +optimizations (-O1 or higher). The behaviour can be changed with two +feature macros: +* __NO_STRING_INLINES: Don't use string optimizations. +* __USE_STRING_INLINES: Use also assembler inline functions (might + increase code use dramatically). + +Since some of these string functions are now additionally defined as +macros, code like "char *strncpy();" doesn't work anymore (and is even +unneccessary since <string.h> has the necessary declarations). Either +change your code or define __NO_STRING_INLINES. + +{UD} Another problem in this area is that the gcc still has problems on +machines with very few registers (e.g., ix86). The inline assembler +code sometimes requires many/all registers and the register allocator +cannot handle these situation in all cases. + +If a function is also defined as a macro in the libc headers one can prevent +the use of the macro easily. E.g., instead of + + cp = strcpy (foo, "lkj"); + +one can write + + cp = (strcpy) (foo, "lkj"); + +Using this method one can avoid using the optimizations for selected +function calls. + + +~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ Answers were given by: {UD} Ulrich Drepper, <drepper@cygnus.com> |