path: root/FAQ

		Frequently Asked Question on GNU C Library

As every FAQ this one also tries to answer questions the user might have
when using the package.  Please make sure you read this before sending
questions or 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 questions you think should be answered in this document,
please let me know.

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

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

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

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

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

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

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

[Q8]	``Can I replace the libc on my Linux system with GNU libc?''

[Q9]	``I expect GNU libc to be 100% source code compatible with
	  the old Linux based GNU libc.  Why isn't it like this?''

[Q10]	``Why does getlogin() always return NULL on my Linux box?''

[Q11]	``Where are the DST_* constants found in <sys/time.h> on many
	  systems?''

[Q12]	``The `gencat' utility cannot process the input which are
	  successfully used on my Linux libc based system.  Why?''

[Q13]	``How do I configure GNU libc so that the essential libraries
	  like libc.so go into /lib and the other into /usr/lib?''

[Q14]	``When linking with the new libc I get unresolved symbols
	  `crypt' and `setkey'.  Why aren't these functions in the
	  libc anymore?''

[Q15]	``What are these `add-ons'?''

[Q16]	``When I use GNU libc on my Linux system by linking against
	  to libc.so which comes with glibc all I get is a core dump.''

[Q17]	``Looking through the shared libc file I haven't found the
	  functions `stat', `lstat', `fstat', and `mknod' and while
	  linking on my Linux system I get error messages.  How is
	  this supposed to work?''

[Q18]	``The prototypes for `connect', `accept', `getsockopt',
	  `setsockopt', `getsockname', `getpeername', `send',
	  `sendto', and `recvfrom' are different in GNU libc than
	  on any other system I saw.  This is a bug, isn't it?''

[Q19]	``My XXX kernel emulates a floating-point coprocessor for me.
	  Should I enable --with-fp?''

[Q20]	``How can I compile gcc 2.7.2.1 from the gcc source code using
	  glibc 2.x?

[Q21]    ``On Linux I've got problems with the declarations in Linux
           kernel headers.''

[Q22]	``When I try to compile code which uses IPv6 header and
	  definitions on my Linux 2.x.y system I am in trouble.
	  Nothing seems to work.''

[Q23]	``When compiling GNU libc I get lots of errors saying functions
	  in glibc are duplicated in libgcc.''

[Q24]	``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.''

[Q25]	``After installing glibc name resolving doesn't work properly.''


[Q26]	``I have /usr/include/net and /usr/include/scsi as symlinks
	  into my Linux source tree.  Is that wrong?''

[Q27]	``Programs like `logname', `top', `uptime' `users', `w' and
	  `who', show incorrect information about the (number of)
	  users on my system.  Why?''

[Q28]	``After upgrading to a glibc 2.1 with symbol versioning I get
	  errors about undefined symbols.  What went wrong?''

[Q29]	``I don't include any kernel header myself but still the
	  compiler complains about type redeclarations of types in the
	  kernel headers.''

[Q30]	``When I start the program XXX after upgrading the library
	  I get
	    XXX: Symbol `_sys_errlist' has different size in shared object, consider re-linking
	  Why?  What to do?''

[Q31]	``What's the problem with configure --enable-omitfp?''

[Q32]	``Why don't signals interrupt system calls anymore?''

[Q33]	``I've got errors compiling code that uses certain string
	  functions.  Why?''

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[Q1]	``What systems does the GNU C Library run 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-gnu	Linux-2.0 on Intel
	m68k-*-linux-gnu	Linux-2.0 on Motorola 680x0
	alpha-*-linux-gnu	Linux-2.0 on DEC Alpha
	powerpc-*-linux-gnu     Linux and MkLinux on PowerPC systems
	sparc-*-linux-gnu	Linux-2.0 on SPARC
	sparc64-*-linux-gnu	Linux-2.0 on UltraSPARC

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

	<bug-glibc@prep.ai.mit.edu>


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[Q2]	``What compiler do I need to build 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 GN