diff options
Diffstat (limited to 'FAQ')
| -rw-r--r-- | FAQ | 73 |
1 files changed, 62 insertions, 11 deletions
@@ -5,7 +5,7 @@ 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 +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. @@ -85,6 +85,8 @@ please let me know. 2.20. What do I need for C++ development? 2.21. Even statically linked programs need some shared libraries which is not acceptable for me. What can I do? +2.22. I just upgraded my Linux system to glibc and now I get + errors whenever I try to link any program. 3. Source and binary incompatibilities, and what to do about them @@ -123,6 +125,7 @@ please let me know. 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? ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ @@ -376,10 +379,10 @@ any other link path. 1.14. What's the problem with configure --enable-omitfp? {AJ} When --enable-omitfp is set the libraries are built without frame -pointers. Some compilers produce buggy code for this model and therefore we +pointers. Some compilers produce buggy code for this model and therefore we don't advise using it at the moment. -If you use --enable-omitfp, you're on your own. If you encounter problems +If you use --enable-omitfp, you're on your own. If you encounter problems with a library that was build this way, we advise you to rebuild the library without --enable-omitfp. If the problem vanishes consider tracking the problem down and report it as compiler failure. @@ -802,6 +805,25 @@ 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. + +2.22. 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. + . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . @@ -995,11 +1017,11 @@ siginterrupt(). 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 +library functions. Some of the functions are additionally implemented as inline functions and others as macros. The optimized string functions are only used when compiling with -optimizations (-O1 or higher). The behavior can be changed with two feature +optimizations (-O1 or higher). The behavior can be changed with two feature macros: * __NO_STRING_INLINES: Don't do any string optimizations. @@ -1008,7 +1030,7 @@ macros: 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 +<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 @@ -1033,22 +1055,37 @@ This disables the optimization for that specific call. {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 +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 +(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: +to do so. For example constructs of the form: enum {foo #define foo foo @@ -1063,7 +1100,7 @@ check with #ifdef). {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 +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). @@ -1134,6 +1171,20 @@ 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 accessable +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. + ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ |