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From: Bruno Haible <bruno@clisp.org>
To: Florian Weimer <fweimer@redhat.com>
Cc: Andreas Schwab <schwab@linux-m68k.org>,
	libc-alpha@sourceware.org, bug-gnulib@gnu.org,
	binutils@sourceware.org
Subject: Re: Undefined use of weak symbols in gnulib
Date: Wed, 28 Apr 2021 16:48:20 +0200	[thread overview]
Message-ID: <3309003.lbPZiPdySv@omega> (raw)
In-Reply-To: <87a6piluow.fsf@oldenburg.str.redhat.com>

Florian Weimer wrote:
> > $ gcc -Wall -fpie -pie foo.c ; ./a.out 
> > initialization code
> >
> > $ gcc -Wall -fpie -pie foo.c -Wl,--no-as-needed -lpthread ; ./a.out
> > multi-threaded initialization
> > initialization code
> >
> > What will change for this program with glibc 2.34?
> 
> If recompiled in this way: The presence of -lpthread will not matter, it
> will always behave is if linked with -lpthread.

So it will print
  multi-threaded initialization
  initialization code
in all cases. This is perfectly fine.

> The relevant scenario here is LD_PRELOAD of a library that depends on
> libpthread.so.0 ...
> If not recompiled and linked without -lpthread against glibc 2.33 or
> earlier, the behavior with the current glibc 2.34 snapshot is
> architecture-dependent and also depends on the binutils version used for
> linking the program.  In some cases, calling pthread_once jumps to
> address zero (causing a crash), or the call to pthread_once is elided
> from the executable.  This scenario can be emulated with older glibc
> using LD_PRELOAD=libpthread.so.0.

I'm confused again. Are you saying that the crash will occur when old
binaries are being used with glibc 2.34 also *without* LD_PRELOAD?

Bruno


  reply	other threads:[~2021-04-28 14:48 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-27  5:53 Undefined use of weak symbols in gnulib Florian Weimer via Libc-alpha
2021-04-27  6:50 ` Paul Eggert
2021-04-27  6:58   ` Florian Weimer via Libc-alpha
2021-04-27  7:13     ` Paul Eggert
2021-04-27  7:24 ` Andreas Schwab
2021-04-27 11:06   ` Florian Weimer via Libc-alpha
2021-04-28  0:09     ` Bruno Haible
2021-04-28  2:10       ` H.J. Lu via Libc-alpha
2021-04-28  2:13         ` H.J. Lu via Libc-alpha
2021-05-05 20:31           ` Fangrui Song
2021-04-28  8:35         ` Florian Weimer via Libc-alpha
2021-04-28 13:15           ` Michael Matz
2021-04-28  7:44       ` Florian Weimer via Libc-alpha
2021-04-28 14:48         ` Bruno Haible [this message]
2021-04-28 17:44           ` Florian Weimer via Libc-alpha
2021-07-17 14:38         ` Bruno Haible
2021-07-17 14:55           ` Florian Weimer via Libc-alpha
2021-07-17 16:39             ` Bruno Haible
2021-07-27 20:02           ` Joseph Myers
2021-07-27 20:19             ` Florian Weimer via Libc-alpha
2021-07-27 23:38               ` Paul Eggert
2021-04-27 23:22   ` Bruno Haible
2021-04-27 23:47 ` Bruno Haible
2021-04-28  7:57   ` Florian Weimer via Libc-alpha
2021-04-28 14:40     ` Bruno Haible
2021-04-28 17:43       ` Florian Weimer via Libc-alpha
2021-04-29 15:15         ` Bruno Haible
2021-04-30  9:55           ` Florian Weimer via Libc-alpha
2021-04-29  6:33       ` Ben Pfaff via Libc-alpha
2021-05-03  1:44 ` Alan Modra via Libc-alpha
2021-07-12 10:04 ` Michael Hudson-Doyle via Libc-alpha
2021-07-12 15:03   ` Florian Weimer via Libc-alpha
2021-07-12 15:30     ` Matthias Klose
2021-07-12 15:37       ` Florian Weimer via Libc-alpha
2021-07-13  0:22         ` Michael Hudson-Doyle via Libc-alpha

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