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Re: Undefined use of weak symbols in gnulib
From: |
Florian Weimer |
Subject: |
Re: Undefined use of weak symbols in gnulib |
Date: |
Tue, 27 Apr 2021 13:06:43 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) |
* Andreas Schwab:
> On Apr 27 2021, Florian Weimer via Binutils wrote:
>
>> I think we can provide an libBrokenGnulib.so preload module which
>> defines pthread_mutexattr_gettype to zero (as an absolute address), so
>> there is a kludge to keep old binaries working, but this is really
>> something that must be fixed in gnulib.
>
> It is likely that the use of weak pthread symbols is not confined to
> gnulib.
True.
Here's a fairly representative test case, I think.
#include <pthread.h>
#include <stdio.h>
extern __typeof (pthread_key_create) __pthread_key_create __attribute__
((weak));
extern __typeof (pthread_once) pthread_once __attribute__ ((weak));
void
f1 (void)
{
puts ("f1 called");
}
pthread_once_t once_var;
void __attribute__ ((weak))
f2 (void)
{
if (__pthread_key_create != NULL)
pthread_once (&once_var, f1);
}
int
main (void)
{
f2 ();
}
Building it with “gcc -O2 -fpie -pie” and linking with binutils 2.30
does not result in a crash with LD_PRELOAD=libpthread.so.0. That's
because the call-to-address-zero via pthread_once has been stubbed out
with NOPs, I think. This is still not correct and will undoubtedly
cause problems because pthread_once is usually called for its side
effect.
With binutils 2.35, the call-to-address-zero is not stubbed out anymore,
but there is still no dynamic symbol reference for pthread_once, so
there is a crash when running with LD_PRELOAD=libpthread.so.0.
This looks like a pre-existing toolchain issue on POWER, related to the
thread I quoted at the start. If we proceed with the glibc libpthread
changes as planned, things might turn out unacceptably bad.
I did a quick experiment and we cannot work around this using a
libpthread.so stub library and compatibility-only symbols in libc.so.6.
Unversioned weak symbols bind to the baseline symbol version, as they
probably should. Even a __pthread_key_create@GLIBC_2.17 compatibility
symbol triggers this issue. I have to think of something else to
salvage this.
Thanks,
Florian
- Undefined use of weak symbols in gnulib, Florian Weimer, 2021/04/27
- Re: Undefined use of weak symbols in gnulib, Paul Eggert, 2021/04/27
- Re: Undefined use of weak symbols in gnulib, Andreas Schwab, 2021/04/27
- Re: Undefined use of weak symbols in gnulib,
Florian Weimer <=
- Re: Undefined use of weak symbols in gnulib, Bruno Haible, 2021/04/27
- Re: Undefined use of weak symbols in gnulib, H.J. Lu, 2021/04/27
- Re: Undefined use of weak symbols in gnulib, H.J. Lu, 2021/04/27
- Re: Undefined use of weak symbols in gnulib, Florian Weimer, 2021/04/28
- Re: Undefined use of weak symbols in gnulib, Michael Matz, 2021/04/28
- Re: Undefined use of weak symbols in gnulib, Florian Weimer, 2021/04/28
- Re: Undefined use of weak symbols in gnulib, Bruno Haible, 2021/04/28
- Re: Undefined use of weak symbols in gnulib, Florian Weimer, 2021/04/28
Re: Undefined use of weak symbols in gnulib, Bruno Haible, 2021/04/27
Re: Undefined use of weak symbols in gnulib, Bruno Haible, 2021/04/27