Frequently Asked Question on GNU C Library

As every FAQ this one also tries to answer the questions the user
might when using the pacakge.  Please make sure you read this before
sending questions/bug reports to the maintainers.

The GNU C Library is very complex.  The building process exploits the
features available in tools generally available.  But many things can
only be done using GNU tools.  Also the code is sometimes hard to
understand because it has to be portable but on the other hand must be
fast.  But you need not understand the details to use GNU C Library.
This will only be necessary if you intend to contribute or change it.

If you have any question which you think might be worth answered in
this document let me know.

						  --drepper@cygnus.com

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[Q1]	``What systems the GNU C Library runs on?''

[A1] {UD} This is difficult to answer.  The file `README' lists the
architectures GNU libc is known to run *at some time*.  This does not
mean that it still can be compiled and run on them in the moment.

The systems glibc is known to work on in the moment and most probably
in the future are:

	*-*-gnu			GNU Hurd
	i[3456]86-*-linux	Linux-2.0 on Intel

Other Linux platforms are also on the way to be supported but I need
some success reports first.

If you have a system not listed above (or in the `README' file) and
you are really interested in porting it, contact

	Roland McGrath		<roland@gnu.ai.mit.edu>
or	Ulrich Drepper		<drepper@cygnus.com>


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[Q2]	``What compiler do I need to translate GNU libc?''

[A2] {UD} It is (almost) impossible to compile GNU C Library using a
different compiler than GNU CC.  A lot of extensions of GNU CC are
used to increase the portability and speed.

But this does not mean you have to use GNU CC for using the GNU C
Library.  In fact you should be able to use the native C compiler
because the success only depends on the binutils: the linker and
archiver.

The GNU CC is found like all other GNU packages on
	ftp://prep.ai.mit.edu/pub/gnu
or better one of the many mirrors.

You always should try to use the latest official release.  Older
versions might not have all the features GNU libc could use.


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[Q3]	``When starting make I get only errors messages.
	  What's wrong?''

[A3] {UD} You definitely need GNU make to translate GNU libc.  No
other make program has the needed functionality.

Versions before 3.74 have bugs which prevent correct execution so you
should upgrade to the latest version before starting the compilation.


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[Q4]	``After I changed configure.in I get `Autoconf version X.Y.
	  or higher is required for this script'.  What can I do?''

[A4] {UD} You have to get the specified autoconf version (or a later)
from your favourite mirror of prep.ai.mit.edu.


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[Q5]	``Do I need a special linker or archiver?''

[A5] {UD} If your native versions are not too buggy you can work with
them.  But GNU libc works best with GNU binutils.

On systems where the native linker does not support weak symbols you
will not get a really 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.


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[Q6]	``Do I need some more things to compile GNU C Library?''

[A6] {UD} Yes, there are some more :-).

* lots of diskspace (for i386-linux this means, e.g., ~70MB)

  You should avoid compiling on a NFS mounted device.  This is very
  slow.

* plenty of time (approx 1h for i386-linux on i586@133 or 2.5h or
  i486@66).

  If you have some more interested measurements let me know.


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[Q7]	``When I run `nm libc.so|grep " U "' on the produced library
	  I still find unresolved symbols?  Can this be ok?''

[A7] {UD} Yes, this is ok.  There can be several kinds of unresolved
symbols:

* magic symbols automatically generated by the linker.  Names are
  often like __start_* and __stop_*-

* symbols resolved by using libgcc.a
  (__udivdi3, __umoddi3, or similar)

* weak symbols, which need not be resolved at all
  (currently fabs among others; this gets resolved if the program
   is linked against libm, too.)

Generally, you should make sure you find a real program which produces
errors while linking.


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Answers were given by:
{UD} Ulrich Drepper, <drepper@cygnus.com>


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