If you have any questions you think should be answered in this document,
please let me know.
- --drepper@cygnus.com
+ --drepper@redhat.com
\f
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
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?
2. Installation and configuration issues
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
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
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.
\f
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
*-*-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
+ 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
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
-egcs (1.0.3 and 1.1.1) should work with the GNU C library (for powerpc see
-question 1.5; for ARM see question 1.6).
+gcc (3.2 or newer) should work with the GNU C library (for MIPS see question 1.20).
-While the GNU CC should be able to compile glibc it is nevertheless adviced
-to use EGCS. Comparing the sizes of glibc on Intel compiled with a recent
-EGCS and gcc 2.8.1 shows this:
-
- text data bss dec hex filename
-egcs-2.93.10 862897 15944 12824 891665 d9b11 libc.so
-gcc-2.8.1 959965 16468 12152 988585 f15a9 libc.so
-
-Make up your own decision.
+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.
{UD} You definitely need GNU make to build GNU libc. No other make
program has the needed functionality.
-We recommend version GNU make version 3.75 or 3.77. Versions before 3.75
-have bugs and/or are missing features. Version 3.76 has bugs which
-appear when building big projects like GNU libc. 3.76.1 appears to work but
-some people have reported problems. If you build GNU make 3.77 from source,
-please read question 4.6 first.
+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?
The static library can be compiled with less featureful tools, but lacks key
features such as NSS.
-For Linux or Hurd, you want binutils 2.8.1.0.23, 2.9.1, or 2.9.1.0.15 or
-higher. These are the only versions we've tested and found reliable. Other
-versions after 2.8.1.0.23 may work but we don't recommend them, especially
-not when C++ is involved. Earlier versions do not work at all.
+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
1.5. Which compiler should I use for powerpc?
-{GK} You want to use egcs 1.1 or later (together with the right versions
-of all the other tools, of course).
-
-In fact, egcs 1.1 has a bug that causes linuxthreads to be
-miscompiled, resulting in segmentation faults when using condition
-variables. There is a temporary patch at:
-
-<http://discus.anu.edu.au/~geoffk/egcs-3.diff>
-
-Later versions of egcs may fix this problem.
+{} Removed. Does not apply anymore.
1.6. Which tools should I use for ARM?
-{PB} You should use egcs 1.1 or a later version. For ELF systems some
-changes are needed to the compiler; a patch against egcs-1.1.x can be found
-at:
-
-<ftp://ftp.netwinder.org/users/p/philb/egcs-1.1.1pre2-diff-981126>
-
-Binutils 2.9.1.0.16 or later is also required.
+{} Removed. Does not apply anymore.
1.7. Do I need some more things to compile the GNU 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 (~170MB for i?86-linux; more for RISC platforms,
- as much as 400MB).
+* lots of disk space (~400MB for i?86-linux; more for RISC platforms).
* plenty of time. Compiling just the shared and static libraries for
- i?86-linux takes approximately 1h on an i586@133, or 2.5h on
- i486@66, or 4.5h on i486@33. 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.
+ 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 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)
+ 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.
If you have some more measurements let me know.
1.9. The compiler hangs while building iconvdata modules. What's
wrong?
-{ZW} This is a problem with old versions of GCC. Initialization of large
-static arrays is very slow. The compiler will eventually finish; give it
-time.
-
-The problem is fixed in egcs 1.1.
+{} Removed. Does not apply anymore.
1.10. When I run `nm -u libc.so' on the produced library I still
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
-crypt package, see question 2.5).
+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
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=crypt,linuxthreads
+ configure --enable-add-ons=linuxthreads
for example.
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?
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, the egcs 1.1 release should be
- ok; gcc 2.8.1 might cause some failures; gcc 2.7.2.x is so buggy that
- explicit checks have been used so that you can't build with it.
+ 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?
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).
+
+For details check also my page <http://www.suse.de/~aj/glibc-mips.html>.
+
+
+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).
+
\f
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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 first. (Do not throw it away; you
- will then lose the ability to compile programs against your old libc.)
+ 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
`crypt' and `setkey'. Why aren't these functions in the
libc anymore?
-{UD} The US places restrictions on exporting cryptographic programs and
-source code. Until this law gets abolished we cannot ship the cryptographic
-functions together with glibc.
-
-The functions are available, as an add-on (see question 1.11). People in the US
-may get it from the same place they got GNU libc from. People outside the
-US should get the code from ftp://ftp.ifi.uio.no/pub/gnu, or another archive
-site outside the USA. The README explains how to install the sources.
-
-If you already have the crypt code on your system the reason for the failure
-is probably that you did not link with -lcrypt. The crypto functions are in
-a separate library to make it possible to export GNU libc binaries from the
-US.
+{} 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
+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
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 2.8.1 or egcs 1.1 (or later versions)
-instead.
+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
-----------------------------------------------------------------------
# Change catalog source in Linux specific format to standard XPG format.
-# Ulrich Drepper <drepper@cygnus.com>, 1996.
+# Ulrich Drepper <drepper@redhat.com>, 1996.
#
/^\$ #/ {
h
byte order independent) or generate it with nisinit from the nis-tools
package; available at
- http://www-vt.uni-paderborn.de/~kukuk/linux/nisplus.html
+ http://www.suse.de/~kukuk/linux/nisplus.html
2.13. I have killed ypbind to stop using NIS, but glibc
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
+ <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:
`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.
+and netgroup are implemented. See also question 2.31.
2.17. I have /usr/include/net and /usr/include/scsi as symlinks
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
+ <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
(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.c \
- -lc -lnss_files -lnss_dns -lresolv
+ 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.
{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 to use more open
+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 (nearly) select free. This means it internally has
-no limits imposed by the `fd_set' type. Instead almost all places where the
+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. The remaining select calls are in the RPC code.
-If your RPC daemons don't need more than FD_SETSIZE file descriptors, you
-don't need to change anything at all.
+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
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 or slang, 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.
+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
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-compat-2.1.tar.gz
+ <ftp://alpha.gnu.org/gnu/glibc/glibc-compat-2.1.tar.gz>
but please keep in mind that it is experimental.
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.
+
+{UD} Only if you are not specifying the --without-cvs flag at configure
+time. This is what you always have to use if you are checking sources
+directly out of the public CVS repository or you have your own private
+repository.
+
+
+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
+
\f
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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.
-{MK} There is however a (partial) solution for this problem. Please take a
-look at the file `login/README.utmpd'.
-
3.3. Where are the DST_* constants found in <sys/time.h> on many
systems?
stdin/stdout/stderr. Why?
{RM,AJ} Constructs like:
-static FILE *InPtr = stdin;
+ 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
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;
-}
+ 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; }
+ 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
{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
-}
+ 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
the Perl db modules the testsuite is not passed. This did not
happen with db-1, gdbm, or ndbm.
-{UD} You are using an outdated copy of the DB_File Perl module. In fact db-2
-finally removed the handling of zero-sized keys which was one of the features
-tested by the old Perl testsuite and therefore you see an error. But this
-never was documented and guaranteed, only broken programs used this feature.
-
-Consequently db-2 does not need to support this feature and instead signals
-an error which leads to easier debugging. The DB_File module maintainer
-Paul Marquess <pmarquess@bfsec.bt.co.uk> acknowledged this change and fixed
-the testsuite so that if you use DB_File v1.60 or later you should not have
-any more problems with db-2.
+{} Removed. Does not apply anymore.
3.14. The pow() inline function I get when including <math.h> is broken.
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?
-{AJ} The GNU C library 2.1 uses db2 instead of db1 which was used in version
-2.0. The internal formats of the actual db files are different. To convert
-the db files from db1 format to db2 format, you can use the programs
-`db_dump185' and `db_load'. Alternativly programs can be linked with db1
-using `-ldb1' instead of linking with db2 which uses `-ldb'. Linking with
-db1 might be preferable if older programs need to access the db file.
+{} 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'"
-db2 supports the old db1 programming interface and also a new programming
-interface. For compilation with the old API, <db_185.h> has to be included
-(and not <db.h>) and you can link with either `-ldb1' or `-ldb' for either
-of the db formats.
+{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.
\f
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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. In particular the getipnodebyname and getipnodebyaddr
-functions are not implemented.
+100% complete.
4.3. When I set the timezone by setting the TZ environment variable
<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
+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>.
4.6. I've build make 3.77 against glibc 2.1 and now make gets
segmentation faults.
-{AJ} GNU make 3.77 has support for 64 bit filesystems which is slightly
-broken (and one of the new features in the GNU C library 2.1 is 64 bit
-filesystem support :-( ). To get a working make you can use either make
-3.75 or patch 3.77. A working patch is available via RedHat's Rawhide server
-(ftp://rawhide.redhat.com/SRPMS/SRPMS/make-3.77-*src.rpm).
+{} 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).
\f
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
Answers were given by:
-{UD} Ulrich Drepper, <drepper@cygnus.com>
-{DMT} David Mosberger-Tang, <davidm@AZStarNet.com>
+{UD} Ulrich Drepper, <drepper@redhat.com>
+{DMT} David Mosberger-Tang, <davidm@hpl.hp.com>
{RM} Roland McGrath, <roland@gnu.org>
-{AJ} Andreas Jaeger, <aj@arthur.rhein-neckar.de>
+{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@vt.uni-paderborn.de>
-{GK} Geoffrey Keating, <geoffk@ozemail.com.au>
+{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>
\f
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