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.
+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.
+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.
1.5. Which compiler should I use for powerpc?
1.6. Do I need some more things to compile GNU C Library?
1.7. What version of the Linux kernel headers should be used?
-1.8. When I run `nm -u libc.so' on the produced library I still
+1.8. The compiler hangs while building iconvdata modules. What's
+ wrong?
+1.9. When I run `nm -u libc.so' on the produced library I still
find unresolved symbols. Can this be ok?
-1.9. What are these `add-ons'?
-1.10. My XXX kernel emulates a floating-point coprocessor for me.
+1.10. What are these `add-ons'?
+1.11. My XXX kernel emulates a floating-point coprocessor for me.
Should I enable --with-fp?
-1.11. When compiling GNU libc I get lots of errors saying functions
+1.12. When compiling GNU libc I get lots of errors saying functions
in glibc are duplicated in libgcc.
-1.12. Why do I get messages about missing thread functions when I use
+1.13. Why do I get messages about missing thread functions when I use
librt? I don't even use threads.
-1.13. What's the problem with configure --enable-omitfp?
+1.14. What's the problem with configure --enable-omitfp?
2. Installation and configuration issues
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.
+{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:
+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
arm-*-none ARM standalone systems
arm-*-linuxaout Linux-2.x on ARM using a.out binaries
-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.
+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, contact
+If you have a system not listed above (or in the `README' file) and you are
+really interested in porting it, contact
<bug-glibc@gnu.org>
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.
+{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 always should try to use the latest official release. Older
-versions may not have all the features GNU libc requires. The current
-releases of egcs (1.0.2) and GNU CC (2.8.1) should work with the GNU C
-library (for powerpc see question question 1.5).
+You always should try to use the latest official release. Older versions
+may not have all the features GNU libc requires. The current releases of
+egcs (1.0.2) and GNU CC (2.8.1) should work with the GNU C library (for
+powerpc see question question 1.5).
1.3. When I try to compile glibc I get only error messages.
What's wrong?
-{UD} You definitely need GNU make to translate GNU libc. No
-other make program has the needed functionality.
+{UD} You definitely need GNU make to translate GNU libc. No other make
+program has the needed functionality.
-We recommend version GNU make version 3.75. Versions 3.76 and 3.76.1
-have bugs which appear when building big projects like GNU libc.
-Versions before 3.74 have bugs and/or are missing features.
+We recommend version GNU make version 3.75. Versions 3.76 and 3.76.1 have
+bugs which appear when building big projects like GNU libc. Versions before
+3.74 have bugs and/or are missing features.
1.4. Do I need a special linker or archiver?
-{UD} You may be able to use your system linker, but GNU libc works
-best with GNU binutils.
+{UD} You may be able to use your system linker, but GNU libc works best with
+GNU binutils.
-On systems where the native linker does not support weak symbols you
-will not get a fully ISO C compliant C library. Generally speaking
-you should use the GNU binutils if they provide at least the same
-functionality as your system's tools.
+On systems where the native linker does not support weak symbols you will
+not get a fully ISO C compliant C library. Generally speaking you should
+use the GNU binutils if they provide at least the same functionality as your
+system's tools.
-Always get the newest release of GNU binutils available. Older
-releases are known to have bugs that prevent a successful compilation.
+Always get the newest release of GNU binutils available. Older releases are
+known to have bugs that prevent a successful compilation.
-{ZW} As of release 2.1 a linker supporting symbol versions is
-required. For Linux, get binutils-2.8.1.0.23 or later. Other systems
-may have native linker support, but it's moot right now, because glibc
-has not been ported to them.
+{ZW} As of release 2.1 a linker supporting symbol versions is required. For
+Linux, get binutils-2.8.1.0.23 or later. Other systems may have native
+linker support, but it's moot right now, because glibc has not been ported
+to them.
1.5. Which compiler should I use for powerpc?
-{GK} You want to use egcs 1.0.1 or later (together with the right
-versions of all the other tools, of course).
+{GK} You want to use egcs 1.0.1 or later (together with the right versions
+of all the other tools, of course).
-In fact, egcs 1.0.1 has a serious bug that prevents a clean make,
-relating to switch statement folding. It also causes the resulting
-shared libraries to use more memory than they should. There is a
-patch at:
+In fact, egcs 1.0.1 has a serious bug that prevents a clean make, relating
+to switch statement folding. It also causes the resulting shared libraries
+to use more memory than they should. There is a patch at:
<http://discus.anu.edu.au/~geoffk/egcs-1.0.1-geoffk.diff>
1.7. 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 when
-using old kernel headers for compiling the GNU C library.
+{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 when using old kernel headers for compiling the GNU C
+library.
+
+
+1.8. The compiler hangs while building iconvdata modules. What's
+ wrong?
+
+{ZW} This is a problem with all current releases of GCC. Initialization of
+large static arrays is very slow. The compiler will eventually finish; give
+it time.
+The problem will be fixed in egcs 1.1 but probably not before then.
-1.8. When I run `nm -u libc.so' on the produced library I still
+
+1.9. 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:
+{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_*
errors while linking before deciding there is a problem.
-1.9. What are these `add-ons'?
+1.10. 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).
+{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).
-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:
+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=crypt,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.
+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.
-1.10. My XXX kernel emulates a floating-point coprocessor for me.
+1.11. 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.
+{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
(libgcc.a for GNU C), because the calling conventions change.
-1.11. When compiling GNU libc I get lots of errors saying functions
+1.12. 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.
+{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.
+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.
+{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.
-1.12. Why do I get messages about missing thread functions when I use
+1.13. 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:
+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.
+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.
-1.13. What's the problem with configure --enable-omitfp?
+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 don't advise using it at the moment.
+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 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.
+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.
-Since a library build with --enable-omitfp is undebuggable on most
-systems, debuggable libraries are also built - you can use it by
-appending "_g" to the library names.
+Since a library build with --enable-omitfp is undebuggable on most systems,
+debuggable libraries are also built - you can use it by appending "_g" to
+the library names.
-The compilation of these extra libraries and the compiler optimizations
-slow down the build process and need more disk space.
+The compilation of these extra libraries and the compiler optimizations slow
+down the build process and need more disk space.
\f
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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.
+{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.
+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
{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.
+/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:
+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.
+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.)
+{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:
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.
+{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.
+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.
+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?
-{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.
+{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 1.9). 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.
+The functions are available, as an add-on (see question 1.10). 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.
+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.
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.
+{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
-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.
+which is the glibc dynamic linker, on Linux systems. On other systems the
+name is /lib/ld.so.1.
-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
+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
- 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:
+Here is what the gcc-2.7.2 specs file should look like when GNU libc is
+installed at /usr:
-----------------------------------------------------------------------
*asm:
-----------------------------------------------------------------------
-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.
+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.
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:
+{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. 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 1.0.2 (or later
-versions) instead.
+{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 1.0.2 (or later versions)
+instead.
2.9. 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.
+{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
+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:
+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.
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
+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
2.11. 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-vt.uni-paderborn.de/~kukuk/linux/nisplus.html).
+{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-vt.uni-paderborn.de/~kukuk/linux/nisplus.html
2.12. 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-glibc3.diff.
+{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-glibc3.diff.
2.13. 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.
+{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.
2.14. 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.
+{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.
2.15. 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.
+{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.
2.16. Programs like `logname', `top', `uptime' `users', `w' and
2.17. 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.
+{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.
+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.
2.18. When I start the program XXX after upgrading the library
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.
+{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.
+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.
+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.
2.19. What do I need for C++ development?
-{HJ,AJ} You need either egcs 1.0.2 or gcc-2.8.1 with libstdc++
-2.8.1 (or more recent versions). 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.
+{HJ,AJ} You need either egcs 1.0.2 or gcc-2.8.1 with libstdc++ 2.8.1 (or
+more recent versions). 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.
2.20. 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.
+{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:
+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.c \
-lc -lnss_files -lnss_dns -lresolv
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
+{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
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.
+{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.
-{MK} There is however a (partial) solution for this problem. Please
-take a look at the file `login/README.utmpd'.
+{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?
-{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).
+{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.
+Instead GNU libc contains zone database support and compatibility code for
+POSIX TZ environment variable handling.
3.4. The prototypes for `connect', `accept', `getsockopt',
`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.
+{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.
+{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.
+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.
+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'.
+{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.
+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.
+{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:
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
+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
-implemented as inline functions and others as macros.
+{AJ} glibc 2.1 has special 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 behavior can be changed with two
-feature macros:
+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.
+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.
+{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
{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.
+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.
+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.
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
}
-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).
+
+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).
+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.
+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.
+{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.
\f
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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.
+{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.
Also, make sure you have a suitably recent kernel. As of the 970401
snapshot, according to Philip Blundell <Philip.Blundell@pobox.com>, the
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, 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 to
-/usr/share/zoneinfo/NAME (NAME is the returned value from tzselect)
-from the file /etc/localtime. 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.
+{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, 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 to /usr/share/zoneinfo/NAME (NAME is the returned value
+from tzselect) from the file /etc/localtime. 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.
\f
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
Local Variables:
mode:outline
outline-regexp:"\\?"
+ fill-column:76
End:
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.
+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.
+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.
?? 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.
+{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:
+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
arm-*-none ARM standalone systems
arm-*-linuxaout Linux-2.x on ARM using a.out binaries
-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.
+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, contact
+If you have a system not listed above (or in the `README' file) and you are
+really interested in porting it, contact
<bug-glibc@gnu.org>
?? 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.
+{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 always should try to use the latest official release. Older
-versions may not have all the features GNU libc requires. The current
-releases of egcs (1.0.2) and GNU CC (2.8.1) should work with the GNU C
-library (for powerpc see question ?powerpc).
+You always should try to use the latest official release. Older versions
+may not have all the features GNU libc requires. The current releases of
+egcs (1.0.2) and GNU CC (2.8.1) should work with the GNU C library (for
+powerpc see question ?powerpc).
?? When I try to compile glibc I get only error messages.
What's wrong?
-{UD} You definitely need GNU make to translate GNU libc. No
-other make program has the needed functionality.
+{UD} You definitely need GNU make to translate GNU libc. No other make
+program has the needed functionality.
-We recommend version GNU make version 3.75. Versions 3.76 and 3.76.1
-have bugs which appear when building big projects like GNU libc.
-Versions before 3.74 have bugs and/or are missing features.
+We recommend version GNU make version 3.75. Versions 3.76 and 3.76.1 have
+bugs which appear when building big projects like GNU libc. Versions before
+3.74 have bugs and/or are missing features.
?? Do I need a special linker or archiver?
-{UD} You may be able to use your system linker, but GNU libc works
-best with GNU binutils.
+{UD} You may be able to use your system linker, but GNU libc works best with
+GNU binutils.
-On systems where the native linker does not support weak symbols you
-will not get a fully ISO C compliant C library. Generally speaking
-you should use the GNU binutils if they provide at least the same
-functionality as your system's tools.
+On systems where the native linker does not support weak symbols you will
+not get a fully ISO C compliant C library. Generally speaking you should
+use the GNU binutils if they provide at least the same functionality as your
+system's tools.
-Always get the newest release of GNU binutils available. Older
-releases are known to have bugs that prevent a successful compilation.
+Always get the newest release of GNU binutils available. Older releases are
+known to have bugs that prevent a successful compilation.
-{ZW} As of release 2.1 a linker supporting symbol versions is
-required. For Linux, get binutils-2.8.1.0.23 or later. Other systems
-may have native linker support, but it's moot right now, because glibc
-has not been ported to them.
+{ZW} As of release 2.1 a linker supporting symbol versions is required. For
+Linux, get binutils-2.8.1.0.23 or later. Other systems may have native
+linker support, but it's moot right now, because glibc has not been ported
+to them.
??powerpc Which compiler should I use for powerpc?
-{GK} You want to use egcs 1.0.1 or later (together with the right
-versions of all the other tools, of course).
+{GK} You want to use egcs 1.0.1 or later (together with the right versions
+of all the other tools, of course).
-In fact, egcs 1.0.1 has a serious bug that prevents a clean make,
-relating to switch statement folding. It also causes the resulting
-shared libraries to use more memory than they should. There is a
-patch at:
+In fact, egcs 1.0.1 has a serious bug that prevents a clean make, relating
+to switch statement folding. It also causes the resulting shared libraries
+to use more memory than they should. There is a patch at:
<http://discus.anu.edu.au/~geoffk/egcs-1.0.1-geoffk.diff>
?? 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 when
-using old kernel headers for compiling the GNU C library.
+{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 when using old kernel headers for compiling the GNU C
+library.
+
+?? The compiler hangs while building iconvdata modules. What's
+ wrong?
+
+{ZW} This is a problem with all current releases of GCC. Initialization of
+large static arrays is very slow. The compiler will eventually finish; give
+it time.
+
+The problem will be fixed in egcs 1.1 but probably not before then.
?? 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:
+{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_*
??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 crypt package, see ?crypt).
+{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 ?crypt).
-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:
+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=crypt,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.
+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.
?? 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.
+{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
?? 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.
+{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.
+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.
+{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:
+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.
+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?
{AJ} When --enable-omitfp is set the libraries are built without frame
-pointers. Some compilers produce buggy code for this model and
-therefore we don't advise using it at the moment.
+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 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.
+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.
-Since a library build with --enable-omitfp is undebuggable on most
-systems, debuggable libraries are also built - you can use it by
-appending "_g" to the library names.
+Since a library build with --enable-omitfp is undebuggable on most systems,
+debuggable libraries are also built - you can use it by appending "_g" to
+the library names.
-The compilation of these extra libraries and the compiler optimizations
-slow down the build process and need more disk space.
+The compilation of these extra libraries and the compiler optimizations slow
+down the build process and need more disk space.
? 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.
+{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.
+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.
+/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:
+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.
+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.)
+{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:
?? 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.
+{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.
+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.
+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?
-{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.
+{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 ?addon). 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.
+The functions are available, as an add-on (see ?addon). 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.
+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.
?? 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.
+{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
-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.
+which is the glibc dynamic linker, on Linux systems. On other systems the
+name is /lib/ld.so.1.
-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
+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
- 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:
+Here is what the gcc-2.7.2 specs file should look like when GNU libc is
+installed at /usr:
-----------------------------------------------------------------------
*asm:
-----------------------------------------------------------------------
-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.
+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.
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:
+{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 )
?? 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 1.0.2 (or later
-versions) instead.
+{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 1.0.2 (or later versions)
+instead.
?? 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.
+{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
+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:
+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.
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
+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
?? 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-vt.uni-paderborn.de/~kukuk/linux/nisplus.html).
+{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-vt.uni-paderborn.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-glibc3.diff.
+{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-glibc3.diff.
?? 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.
+{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.
+{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.
?? 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.
+{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)
?? 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.
+{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.
+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
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.
+{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.
+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.
+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 1.0.2 or gcc-2.8.1 with libstdc++
-2.8.1 (or more recent versions). 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.
+{HJ,AJ} You need either egcs 1.0.2 or gcc-2.8.1 with libstdc++ 2.8.1 (or
+more recent versions). 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.
?? 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.
+{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:
+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.c \
-lc -lnss_files -lnss_dns -lresolv
?? 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
+{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
??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.
+{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.
-{MK} There is however a (partial) solution for this problem. Please
-take a look at the file `login/README.utmpd'.
+{MK} There is however a (partial) solution for this problem. Please take a
+look at the file `login/README.utmpd'.
?? 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).
+{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.
+Instead GNU libc contains zone database support and compatibility code for
+POSIX TZ environment variable handling.
?? 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.
+{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.
+{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.
+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.
+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'.
+{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.
+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.
+{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:
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
+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
-implemented as inline functions and others as macros.
+{AJ} glibc 2.1 has special 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 behavior can be changed with two
-feature macros:
+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.
+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.
+{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
{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.
+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.
+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.
?? 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
}
-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).
+
+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).
+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.
+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.
+{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.
? Miscellaneous
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.
+{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.
Also, make sure you have a suitably recent kernel. As of the 970401
snapshot, according to Philip Blundell <Philip.Blundell@pobox.com>, the
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, 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 to
-/usr/share/zoneinfo/NAME (NAME is the returned value from tzselect)
-from the file /etc/localtime. 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.
+{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, 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 to /usr/share/zoneinfo/NAME (NAME is the returned value
+from tzselect) from the file /etc/localtime. 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.
\f
Answers were given by:
Local Variables:
mode:outline
outline-regexp:"\\?"
+ fill-column:76
End:
+1998-04-21 Ulrich Drepper <drepper@cygnus.com>
+
+ * ptlongjmp.c: Add prorotypes for __libc_siglongjmp and
+ __libc_longjmp.
+
1998-04-20 14:55 Ulrich Drepper <drepper@cygnus.com>
* Makefile (libpthread-routines): Add ptlongjmp and spinlock.
#include "pthread.h"
#include "internals.h"
+/* These functions are not declared anywhere since they shouldn't be
+ used at another place but here. */
+extern void __libc_siglongjmp (sigjmp_buf env, int val)
+ __attribute__ ((noreturn));
+extern void __libc_longjmp (sigjmp_buf env, int val)
+ __attribute__ ((noreturn));
+
+
static void pthread_cleanup_upto(__jmp_buf target)
{
pthread_descr self = thread_self();
If you do not wish to use some add-on package that you have present in
your source tree, give this option a list of the add-ons that you
@emph{do} want used, like this: @samp{--enable-add-ons=crypt,linuxthreads}
+
+@item --with-headers=DIRECTORY
+Search only DIRECTORY and the C compiler's private directory for header
+files not found in the libc sources. @file{/usr/include} will not be
+searched if this option is given. On Linux, DIRECTORY should be the
+kernel's private include directory (usually
+@file{/usr/src/linux/include}).
+
+This option is primarily of use on a system where the headers in
+@file{/usr/include} come from an older version of glibc. Conflicts can
+occasionally happen in this case. Note that Linux libc5 qualifies as an
+older version of glibc. You can also use this option if you want to
+compile glibc with a newer set of kernel headers than the ones found in
+@file{/usr/include}.
@end table
You should not build the library in the same directory as the sources,
the GNU C compiler, so you may need to compile the library with GCC.
(In fact, all of the existing complete ports require GCC.)
-
To build the library and related programs, type @code{make}. This will
produce a lot of output, some of which may look like errors from
@code{make} (but isn't). Look for error messages from @code{make}
containing @samp{***}. Those indicate that something is really wrong.
+The compilation process takes several hours even on fast hardware;
+expect at least two hours for the default configuration on i586 for
+Linux. For Hurd times are much longer. All current releases of GCC
+have a problem which causes them to take several minutes to compile
+certain files in the iconvdata directory. Do not panic if the compiler
+appears to hang.
+
To build and run some test programs which exercise some of the library
facilities, type @code{make check}. This will produce several files
with names like @file{@var{program}.out}.