glibc/FAQ
Ulrich Drepper 68dbb3a69e update from main archive 961214
Sun Dec 15 01:53:20 1996  Ulrich Drepper  <drepper@cygnus.com>

	* Makefile (subdirs): Change crypt to md5-crypt.
	* crypt/Makefile, crypt/md5-crypt.c, crypt/md5.c, crypt/md5.h,
	crypt/md5c-test.c, crypt/md5test.c: Move to new directory
	md5-crypt.
	* sysdeps/unix/sysv/linux/configure.in: Refer to linuxthreads and
	crypt instead of LinuxThreads and des-crypt.

	* Makefile (subdirs): Add nss back.
	* sysdeps/unix/inet/Subdirs: Move nis to end of file to fulfill
	dependencies.

	* libio/iofclose.c: Implement fclose(NULL) as closing all streams.
	* stdio-common/Makefile (routines): Add fcloseall.
	* stdio-common/fcloseall.c: New file.
	* sysdeps/generic/abort.c: Make implementation POSIX.1 compatible.

	* sysdeps/mach/libc-lock.h: Add definition of __libc_lock_trylock.
	* sysdeps/stub/libc-lock.h: Define __libc_lock_trylock to always
	return 0.

	* stdio-common/printf.h: Define MIN and MAX only if not already
	defined.

	* stdio-common/vfprintf.c: Set errno to EBADF if stream does not
	allow writing.  Required by POSIX.1.

	* libio/libioP.h (CHECK_FILE): Use MAYBE_SET_EINVAL instead of
	assignment.

	* interp.c: Update copyright.
	* libio/clearerr.c: Likewise.
	* libio/ioseekoff.c: Likewise.
	* libio/ioseekpos.c: Likewise.
	* stdio/fclose.c: Likewise.
	* stdio/fflus.c: Likewise.

	* libio/libio.h [!_IO_MTSAFE_IO]: Define _IO_cleanup_region_start
	and _IO_cleanup_region_end as empty.
	* libio/fgetc.c: Use _IO_cleanup_region_start and
	_IO_cleanup_region_end instead of __libc_cleanup_region_start and
	__libc_cleanup_region_end.
	* libio/fputc.c: Likewise.
	* libio/freopen.c: Likewise.
	* libio/fseek.c: Likewise.
	* libio/getc.c: Likewise.
	* libio/getchar.c: Likewise.
	* libio/iofclose.c: Likewise.
	* libio/iofflush.c: Likewise.
	* libio/iofgetpos.c: Likewise.
	* libio/iofgets.c: Likewise.
	* libio/iofputs.c: Likewise.
	* libio/iofread.c: Likewise.
	* libio/iofsetpos.c: Likewise.
	* libio/ioftell.c: Likewise.
	* libio/iofwrite.c: Likewise.
	* libio/iogetdelim.c: Likewise.
	* libio/iogets.c: Likewise.
	* libio/ioputs.c: Likewise.
	* libio/iosetbuffer.c: Likewise.
	* libio/iosetvbuf.c: Likewise.
	* libio/ioungetc.c: Likewise.

	* libio/iovspintf.c: Use cleanup handler to make sure no dangling
	locks can stay over.
	* libio/iovsscanf.c: Likewise.

	* libio/genops.c: Use _IO_lock_init_recursive and _IO_lock_fini
	instead of __libc_lock_init_recursive and __libc_lock_fini.

	* libio/filedoalloc.c: Only use __isatty when compiling GNU libc.
	Otherwise use isatty.
	* libio/fileops.c: Likewise for __open and open.

	* login/utmp_file.c (getutent_r_file): Use fcntl instead of
	flock.

	* nis/ypclnt.h: Add more casts to prevent warnings.

	* nss/Makefile (services): Remove dns.
	(libnss_dns, libnss_dns-inhibit-o): Remove definition.
	($(objpfx)libnss_dns.so): Removed.
	* nss/nss_dns/dns-host.c, nss/nss_dns/dns-network.c: Moved to...
	* resolv/nss_dns: ...here.
	* resolv/Makefile (extra-libs): Add libnss_dns.
	(libnss_dns-routines, libnss_dns-inhibit-o): Define as in
	nss/Makefile.

	* nss/XXX-lookup.c: Call __nss_database_lookup with new argument
	specifying alternate name for entry in /etc/nsswitch.conf
	* nss/nsswitch.c: If no entry with primary name is found in
	/etc/nsswitch.conf try alternate name if given.
	* nss/nsswitch.h: Add new parameter in prototype for
	__nss_database_lookup.
	* nss/spwd-lookup.c: Provide alternative entry name to look for.
	This makes our NSS compatible with Solaris' nsswitch.conf files.

	* string/tst-strlen.c: Change all counting variables to type size_t
	to prevent warnings.

	* sysdeps/posix/fpathconf.c: Update copyright.
	* sysdeps/posix/pathconf.c: Don't call fpathconf to do the work.
	Opening the file at this path may fail if it is a FIFO or pipe.

	These changes make the time implementation POSIX.1 compliant.
	* time/localtime.c (__localtime_r): Always call __tzset not only
	if __tzset_run is zero.
	* time/strftime.c: Add definition of memset_space to help to
	reduce for systems which have memset.
	(strftime): Don't use tm_zone member of argument for zone name.
	Instead always use tzname[].
	Call tzset() as required by POSIX.1 before any action.
	* time/tzset.c (tzset): Set tzname[] as required by POSIX.1.
	Remove global variable __tzset_run.  __tzset is now called always
	when a dependent function is used.
	(__tzset): Caching happens based on the contents of the
	environment variable TZ.

Fri Dec 13 01:06:52 1996  Andreas Schwab  <schwab@issan.informatik.uni-dortmund.de>

	* sysdeps/unix/sysv/linux/paths.h: Add _PATH_KLOG.

Thu Dec 12 09:16:35 1996  Andreas Schwab  <schwab@issan.informatik.uni-dortmund.de>

	* rellns-sh: Correctly handle a relative source file name.

Wed Dec 11 19:18:40 1996  Andreas Schwab  <schwab@issan.informatik.uni-dortmund.de>

	* login/utmp_file.c (setutent_file): Seek back to beginning of the
	file if resetting.

Thu Dec 12 16:39:12 1996  Thomas Bushnell, n/BSG  <thomas@gnu.ai.mit.edu>

	* hurd/hurdinit.c (map0): Delete function.  Don't do this on
	_hurd_preinit_hook.
	* hurd/hurdstartup.c (_hurd_startup): Map page zero redzone here.
1996-12-15 02:15:29 +00:00

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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
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
[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?
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
[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
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>
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
[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 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 mirror sites.
You always should try to use the latest official release. Older
versions might not have all the features GNU libc could use.
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
[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.
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
[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.
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
[Q5] ``Do I need a special linker or archiver?''
[A5] {UD} If your native versions are not too buggy you can probably
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.
Always get the newest release of GNU binutils available.
Older releases are known to have bugs that affect building the GNU C
Library.
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
[Q6] ``Do I need some more things to compile GNU C Library?''
[A6] {UD} Yes, there are some more :-).
* GNU gettext; the GNU libc is internationalized and partly localized.
For bringing the messages for the different languages in the needed
form the tools from the GNU gettext package are necessary. See
ftp://prep.ai.mit.edu/pub/gnu or better any mirror site.
* lots of diskspace (for i?86-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 i?86-linux on i586@133 or 2.5h on
i486@66 or 4.5h on i486@33). For Hurd systems times are much higher.
If you have some more measurements let me know.
* When compiling for Linux:
+ the header files of the Linux kernel must be available in the
search path of the CPP as <linux/*.h> and <asm/*.h>.
* Some files depend on special tools. E.g., files ending in .gperf
need a `gperf' program. The GNU version (part of libg++) is known
to work while some vendor versions do not.
You should not need these tools unless you change the source files.
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
[Q7] ``When I run `nm -u libc.so' 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 starting with _dl_* come from the dynamic linker
* 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 before deciding there is a problem.
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
[Q8] ``Can I replace the libc on my Linux system with GNU libc?''
[A8] {UD} You cannot replace any existing libc for Linux with GNU
libc. There are different versions of C libraries and you can run
libcs with different major version independently.
For Linux there are today two libc versions:
libc-4 old a.out libc
libc-5 current ELF libc
GNU libc will have the major number 6 and therefore you can have this
additionally 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.
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
[Q9] ``I expect GNU libc to be 100% source code compatible with
the old Linux based GNU libc. Why isn't it like this?''
[A9] {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 now can be corrected. Here is a list of the known source code
incompatibilities:
* _GNU_SOURCE: glibc does not automatically define _GNU_SOURCE. Thus,
if a program depends on GNU extensions or some other non-standard
functionality, it is necessary to compile it with C compiler option
-D_GNU_SOURCE, or better, to put `#define _GNU_SOURCE' at the beginning
of your source files, before any C library header files are included.
This difference normally manifests itself in the form of missing
prototypes and/or data type definitions. Thus, if you get such errors,
the first thing you should do is try defining _GNU_SOURCE and see if
that makes the problem go away.
For more information consult the file `NOTES' part of the GNU C
library sources.
* reboot(): GNU libc sanitizes the interface of reboot() to be more
compatible with the interface used on other OSes. In particular,
reboot() as implemented in glibc takes just one argument. This argument
corresponds to the third argument of the Linux reboot system call.
That is, a call of the form reboot(a, b, c) needs to be changed into
reboot(c).
Beside this the header <sys/reboot.h> defines the needed constants
for the argument. These RB_* constants should be used instead of the
cryptic magic numbers.
* swapon(): the interface of this function didn't changed, but the
prototype is in a separate header file <sys/swap.h>. For the additional
argument of of swapon() you should use the SWAP_* constants from
<linux/swap.h>, which get defined when <sys/swap.h> is included.
* errno: If a program uses variable "errno", then it _must_ include header
file <errno.h>. The old libc often (erroneously) declared this variable
implicitly as a side-effect of including other libc header files. glibc
is careful to avoid such namespace pollution, which, in turn, means that
you really need to include the header files that you depend on. This
difference normally manifests itself in the form of the compiler
complaining about the references of the undeclared symbol "errno".
* Linux-specific syscalls: All Linux system calls now have appropriate
library wrappers and corresponding declarations in various header files.
This is because the syscall() macro that was traditionally used to
work around missing syscall wrappers are inherently non-portable and
error-prone. The following tables lists all the new syscall stubs,
the header-file declaring their interface and the system call name.
syscall name: wrapper name: declaring header file:
------------- ------------- ----------------------
bdflush bdflush <sys/kdaemon.h>
create_module create_module <sys/module.h>
delete_module delete_module <sys/module.h>
get_kernel_syms get_kernel_syms <sys/module.h>
init_module init_module <sys/module.h>
syslog ksyslog_ctl <sys/klog.h>
* lpd: Older versions of lpd depend on a routine called _validuser().
The library does not provide this function, but instead provides
__ivaliduser() which has a slightly different interfaces. Simply
upgrading to a newer lpd should fix this problem (e.g., the 4.4BSD
lpd is known to be working).
* resolver functions/BIND: like on many other systems the functions of
the resolver library are not included in the libc itself. There is
a separate library libresolv. If you find some symbols starting with
`res_*' undefined simply add -lresolv to your call of the linker.
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
[Q10] ``Why does getlogin() always return NULL on my Linux box?''
[A10] {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. So the
record size is different, fields might have a different position and
so reading 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.
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
[Q11] ``Where are the DST_* constants found in <sys/time.h> on many
systems?''
[A11] {UD} These constants come from the old BSD days and are not used
today anymore (even the Linux based glibc does not implement the handling
although the constants are defined).
Instead GNU libc contains the zone database handling and compatibility
code for POSIX TZ environment variable handling.
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
[Q12] ``The `gencat' utility cannot process the input which are
successfully used on my Linux libc based system. Why?''
[A12] {UD} Unlike the author of the `gencat' program which is distributed
with Linux libc I have read the underlying standards before writing the
code. It is completely compatible with the specification given in
X/Open Portability Guide.
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
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:
-----------------------------------------------------------------------
# Change catalog source in Linux specific format to standard XPG format.
# Ulrich Drepper <drepper@cygnus.com>, 1996.
#
/^\$ #/ {
h
s/\$ #\([^ ]*\).*/\1/
x
s/\$ #[^ ]* *\(.*\)/\$ \1/
}
/^# / {
s/^# \(.*\)/\1/
G
s/\(.*\)\n\(.*\)/\2 \1/
}
-----------------------------------------------------------------------
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
[Q13] ``How do I configure GNU libc so that the essential libraries
like libc.so go into /lib and the other into /usr/lib?''
[A13] {UD} Like all other GNU packages GNU libc is configured to use a
base directory and install all files relative to this. If you intend
to really use GNU libc on your system this base directory is /usr. I.e.,
you run
configure --prefix=/usr <other_options>
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.
To install the essential libraries which come with GNU libc in /lib
one must explicitly tell this. Autoconf has no option for this so you
have to use the file where all user supplied additional information
should go in: `configparms' (see the `INSTALL' file). For Linux the
`configparms' file should contain:
slibdir=/lib
sysconfdir=/etc
The first line specifies the directory for the essential libraries,
the second line the directory for file which are by tradition placed
in a directory named /etc.
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
[Q14] ``When linking with the new libc I get unresolved symbols
`crypt' and `setkey'. Why aren't these functions in the
libc anymore?''
[A14] {UD} Remember the US restrictions of exporting cryptographic
programs and source code. Until this law gets abolished we cannot
ship the cryptographic function together with the libc.
But of course we provide the code and there is an very easy way to use
this code. First get the extra package. People in the US way get it
from the same place they got the GNU libc from. People outside the US
should get the code from ftp.uni-c.dk [129.142.6.74], 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 failed to link with -lcrypt. The crypto
functions are in a separate library to make it possible to export GNU
libc binaries from the US.
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
[Q15] ``What are these `add-ons'?''
[A15] {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 Q14).
To ease the use as part of GNU libc the installer just has to unpack
the package and tell the configuration script about these additional
subdirectories using the --enable-add-ons option. When you add the
crypt add-on you just have to use
configure --enable-add-ons=crypt,XXX ...
where XXX are possible other add-ons and ... means the rest of the
normal option list.
You can use add-ons also to overwrite some files in glibc. The add-on
system dependent subdirs are search first. It is also possible to add
banner files (use a file named `Banner') or create shared libraries.
Using add-ons has the big advantage that the makefiles of the GNU libc
can be used. Only some few stub rules must be written to get
everything running. Even handling of architecture dependent
compilation is provided. The GNU libc's sysdeps/ directory shows how
to use this feature.
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
[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.''
[A16] {UD} It is not enough to simply link against the GNU libc
library itself. The GNU C library comes with its own dynamic linker
which really conforms to the ELF API standard. This dynamic linker
must be used.
Normally this is done by the compiler. The gcc will use
-dynamic-linker /lib/ld-linux.so.1
unless the user specifies her/himself a -dynamic-linker argument. But
this is not the correct name for the GNU dynamic linker. The correct
name is /lib/ld.so.1 which is the name specified in the SVr4 ABi.
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
In this file you have to change a few things:
- change `ld-linux.so.1' to `ld.so.1' (or to ld-linux.so.2, see below)
- remove all expression `%{...:-lgmon}'; there is no libgmon in glibc
Things are getting 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. Here is for
example the gcc-2.7.2 specs file when GNU libc is installed at
/usr:
-----------------------------------------------------------------------
*asm:
%{V} %{v:%{!V:-V}} %{Qy:} %{!Qn:-Qy} %{n} %{T} %{Ym,*} %{Yd,*} %{Wa,*:%*}
*asm_final:
%{pipe:-}
*cpp:
%{fPIC:-D__PIC__ -D__pic__} %{fpic:-D__PIC__ -D__pic__} %{!m386:-D__i486__} %{posix:-D_POSIX_SOURCE} %{pthread:-D_REENTRANT}
*cc1:
%{profile:-p}
*cc1plus:
*endfile:
%{!shared:crtend.o%s} %{shared:crtendS.o%s} crtn.o%s
*link:
-m elf_i386 %{shared:-shared} %{!shared: %{!ibcs: %{!static: %{rdynamic:-export-dynamic} %{!dynamic-linker:-dynamic-linker /lib/ld-linux.so.2}} %{static:-static}}}
*lib:
%{!shared: %{pthread:-lpthread} %{profile:-lc_p} %{!profile: -lc}}
*libgcc:
-lgcc
*startfile:
%{!shared: %{pg:gcrt1.o%s} %{!pg:%{p:gcrt1.o%s} %{!p:%{profile:gcrt1.o%s} %{!profile:crt1.o%s}}}} crti.o%s %{!shared:crtbegin.o%s} %{shared:crtbeginS.o%s}
*switches_need_spaces:
*signed_char:
%{funsigned-char:-D__CHAR_UNSIGNED__}
*predefines:
-D__ELF__ -Dunix -Di386 -Dlinux -Asystem(unix) -Asystem(posix) -Acpu(i386) -Amachine(i386)
*cross_compile:
0
*multilib:
. ;
-----------------------------------------------------------------------
The above is currently correct for ix86/Linux. Because of
compatibility issues on this platform the dynamic linker must have
a different name: ld-linux.so.2. So you have to replace
%{!dynamic-linker:-dynamic-linker=/home/gnu/lib/ld-linux.so.2}
by
%{!dynamic-linker:-dynamic-linker=/home/gnu/lib/ld.so.1}
in the above example specs file ti make it work for other systems.
Future versions of GCC will automatically provide the correct specs.
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
[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?''
[A17] {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 ld.so.1 libc.a )
{UD} The Linux ldconfig file probably generates a link libc.so ->
libc.so.6 in /lib. This is not correct. There must not be such a
link. The linker script with the above contents is placed in
/usr/lib which is enough for the linker.
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
[Q18] ``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?''
[A18] {UD} No, this is no bug. This version of the GNU libc already
follows the to-be-released POSIX.1g standard. In this standard
the type `size_t' is used for all parameters which describe a size.
So better change now.
This change is critical for system which have
sizeof (int) != sizeof (size_t)
like the Alpha.
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
[Q19] ``My XXX kernel emulates a floating-point coprocessor for me.
Should I enable --with-fp?''
[A19] {UD} As `configure --help' shows the default value is `yes' and
this should not be changed unless the FPU instructions would be
invalid. I.e., an emulated FPU is for the libc as good as a real one.
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
[Q20] ``How can I compile gcc 2.7.2.1 from the gcc source code using
glibc 2.x?
[A20] {HJL} There is no support in gcc for glibc 2.0 before gcc 2.8. It
is very tricky to compile gcc 2.7.2.1 using glibc 2.x. You have to
build it manually or with one pass only. You also have to use the
specs file in this FAQ while compiling gcc.
A pre-compiled binary version of gcc 2.7.2.1 linked with glibc 2.x for
Linux/x86 is available in the same directory at the glibc 2.x source
code ftp sites.
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
Answers were given by:
{UD} Ulrich Drepper, <drepper@cygnus.com>
{DMT} David Mosberger-Tang, <davidm@AZStarNet.com>
{RM} Roland McGrath, <roland@gnu.ai.mit.edu>
{HJL} H.J. Lu, <hjl@gnu.ai.mit.edu>
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