Re: support for multithread-safe libraries

[Albert Chin]

On Thu, Jul 14, 2005 at 04:10:14PM +0200, Bruno Haible wrote:
> I propose to add a new module 'lock' to gnulib. It addresses these problems.
> It will be used in gettext 0.15.

I looked through m4/lock.m4 to determine how you identify weak symbol
support on a system:
    gl_have_weak=no
    AC_TRY_LINK([extern void xyzzy ();
#pragma weak xyzzy], [xyzzy();], [gl_have_weak=yes])

I'm mainly interested with the vendor compiler, not GCC.

  $ cat weak.c
extern void xyzzy ();
#pragma weak xyzzy

int
main (void) {
  xyzzy();
}

  (Solaris 2.6, 7, 8, 9, 10/SPARC)
  $ cc weak.c

  (HP-UX 11.00, 11i)
  $ cc weak.c
cc: "weak.c", line 2: warning 21: Undefined pragma "WEAK" ignored.
/usr/ccs/bin/ld: Unsatisfied symbols:
   xyzzy (first referenced in weak.o) (code)

  (AIX 4.3.3, 5.1, 5.2)
  $ cc weak.c
ld: 0711-317 ERROR: Undefined symbol: .xyzzy
ld: 0711-345 Use the -bloadmap or -bnoquiet option to obtain more information.

  (Tru64 UNIX 4.0D, 5.1)
  $ cc weak.c
ld:
Unresolved:
xyzzy

  (IRIX 6.5)
  $ cc weak.c

So, according to your test, #pragma weak supports weak symbols on
Solaris and IRIX 6.5. However, in the case of pthread mutex'es, you
should really test for working stubs in libc:
  http://lists.freedesktop.org/archives/cairo/2005-July/004465.html

If you do so, you'll get a failure on IRIX 6.5 and a success on HP-UX
11.x.

Some interesting references:
  http://gcc.gnu.org/ml/gcc-help/2005-07/msg00095.html
  
http://groups-beta.google.com/group/comp.sys.sgi.admin/browse_thread/thread/4586067cd05bb6cb/d971cc2459ec0ded?q=pthread+group:comp.sys.sgi.admin+author:albert+author:chin&rnum=1&hl=en#d971cc2459ec0ded

-- 
albert chin (address@hidden)