Re: libanl + atexit + more

[Andreas Jaeger <aj at suse dot de>]

Jakub Jelinek <jakub@redhat.com> writes:

> On Mon, Mar 05, 2001 at 09:51:37PM +0100, Andreas Jaeger wrote:
> > Andreas Jaeger <aj@suse.de> writes:
> > 
> > > Ulrich Drepper <drepper@redhat.com> writes:
> > > 
> > > > Second, I haven't gotten any comments on the atexit() implementation
> > > > changes I made.  They are so non-obvious that I thought the one or
> > > > other would comment.  The good thing is that this implementation
> > > > should be very robust.  The bad thing is that old programs cannot be
> > > > fixed, everything (means DSOs) has to be relinked (if they have this
> > > > problem which is fortunately rare).  I don't think this is a problem.
> > > > Note that today (until sometime next week :-) this atexit()
> > > > implementation is not Unix conforming.  Unix currently forbids this
> > > > behavior (this means the registered functions are called at dlclose()
> > > > time).  I've filed an defect report which will be handled next week.
> > > 
> > > make check fails now for me:
> > > 
> > > GCONV_PATH=/builds/glibc/main-gcc-2.95/iconvdata LC_ALL=C   /builds/glibc/main-gcc-2.95/elf/ld-linux.so.2 --library-path /builds/glibc/main-gcc-2.95:/builds/glibc/main-gcc-2.95/math:/builds/glibc/main-gcc-2.95/elf:/builds/glibc/main-gcc-2.95/dlfcn:/builds/glibc/main-gcc-2.95/nss:/builds/glibc/main-gcc-2.95/nis:/builds/glibc/main-gcc-2.95/rt:/builds/glibc/main-gcc-2.95/resolv:/builds/glibc/main-gcc-2.95/crypt:/builds/glibc/main-gcc-2.95/linuxthreads /builds/glibc/main-gcc-2.95/dlfcn/tstcxaatexit  > /builds/glibc/main-gcc-2.95/dlfcn/tstcxaatexit.out
> > > make[2]: *** [/builds/glibc/main-gcc-2.95/dlfcn/tstcxaatexit.out] Error 1
> > > 
> > > gromit:/builds/glibc/main-gcc-2.95:[0]$ cat dlfcn/tstcxaatexit.out 
> > > cannot open "modcxaatexit.so": /builds/glibc/main-gcc-2.95/dlfcn/modcxaatexit.so: undefined symbol: __dso_handle
> 
> This one can be compiled with something like:
> 
> --- libc/dlfcn/modcxaatexit.c.jj	Mon Feb 26 18:41:22 2001
> +++ libc/dlfcn/modcxaatexit.c	Tue Mar  6 16:34:53 2001
> @@ -33,7 +33,7 @@ fluffy (void *p)
>  void
>  bar (void *p)
>  {
> -  extern void *__dso_handle;
> +  extern void *__dso_handle __attribute__ ((__weak__));
>    printf ("This is %s\n", __FUNCTION__);
> -  __cxa_atexit (fluffy, p, __dso_handle);
> +  __cxa_atexit (fluffy, p, &__dso_handle ? __dso_handle : NULL);
>  }
> 
> (but the test will fail anyway).
> > > 
> > > This is with gcc 2.95.2.  With a 3.0 pre release I get a segmentation
> > > fault, I'll send details tomorrow.
> > 
> > It's not tomorrow ;-) but here's the failure:
> > 
> > gromit:/usr/src/cvs/libc/dlfcn:[0]$ GCONV_PATH=/builds/glibc/20010106-gcc-2.97.test/iconvdata LC_ALL=C   /builds/glibc/20010106-gcc-2.97.test/elf/ld-linux.so.2 --library-path /builds/glibc/20010106-gcc-2.97.test:/builds/glibc/20010106-gcc-2.97.test/math:/builds/glibc/20010106-gcc-2.97.test/elf:/builds/glibc/20010106-gcc-2.97.test/dlfcn:/builds/glibc/20010106-gcc-2.97.test/nss:/builds/glibc/20010106-gcc-2.97.test/nis:/builds/glibc/20010106-gcc-2.97.test/rt:/builds/glibc/20010106-gcc-2.97.test/resolv:/builds/glibc/20010106-gcc-2.97.test/crypt:/builds/glibc/20010106-gcc-2.97.test/linuxthreads /builds/glibc/20010106-gcc-2.97.test/dlfcn/tstcxaatexit
> > This is bar
> > module unload didn't change `v'
> > Segmentation fault
> 
> But this one is IMHO more problematic. Initially I thought it is just that
> libc_nonshared.a is not being dragged into DSOs built during glibc make, so
> I have hacked up Makerules so that it drags in libc_nonshared.a and libc.so
> if libc.so was requested (and did this outside of -Wl,--(no-)whole-archive
> pair), but that did not fix things up, since gcc's crtstuff has this in:
> 
> /* This is a kludge. The i386 GNU/Linux dynamic linker needs ___brk_addr,
>    __environ and atexit (). We have to make sure they are in the .dynsym
>    section. We accomplish it by making a dummy call here. This
>    code is never reached.  */
> 
> #if defined(__linux__) && defined(__PIC__) && defined(__i386__)
>   {
>     extern void *___brk_addr;
>     extern char **__environ;
> 
>     ___brk_addr = __environ;
>     atexit (0);
>   }
> #endif
> 
> and so atexit ends up unversioned and undefined.
> Perhaps we could change the order in libc.so linker script to
> libc_nonshared.a libc.so and change atexit in glibc back to normal symbol
> again, so that it catches up crtendS.o which comes last (well, before crtn.o
> but there is just one for both shared and non-shared).

I've updated my binutils, rebuild glibc and now it works - I'll retry
on the other machine where I noticed this problem later today.

Andreas
-- 
 Andreas Jaeger
  SuSE Labs aj@suse.de
   private aj@arthur.inka.de
    http://www.suse.de/~aj