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From: "wintersonnenwende at yandex dot ru" <sourceware-bugzilla@sourceware.org>
To: glibc-bugs@sourceware.org
Subject: [Bug nptl/12310] pthread_exit() in main thread segfaults when statically-linked
Date: Fri, 17 May 2013 14:14:00 -0000
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X-Bugzilla-Who: wintersonnenwende at yandex dot ru
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http://sourceware.org/bugzilla/show_bug.cgi?id=12310

Vladimir Nikulichev <wintersonnenwende at yandex dot ru> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |wintersonnenwende at yandex
                   |                            |dot ru

--- Comment #2 from Vladimir Nikulichev <wintersonnenwende at yandex dot ru> 2013-05-17 14:14:23 UTC ---
I reproduced it with glibc 2.12.2, gcc 4.4.6, binutils 2.20.1.
It is a linking issue. Look at a file csu/libc-start.c:

//=======================================================

  extern unsigned int __nptl_nthreads __attribute ((weak));
  unsigned int *const ptr = &__nptl_nthreads;

    if (! atomic_decrement_and_test (ptr))
  /* Not much left to do but to exit the thread, not the process.  */
  __exit_thread (0);

//=======================================================

This atomic_decrement_and_test finally looks like this:
0x0000000000400629 <+489>:    lock decl -0x400630(%rip)        # 0x0
0x0000000000400630 <+496>:    sete   %dl

So it seems that address of __nptl_nthreads became NULL after linking. The
variable is stored in file nptl/pthread_create.c. The program above will work
fine if you add dummy call to pthread_create():

$ cat exit.c 
#include <pthread.h>

void foo() {
  pthread_create(NULL, NULL, NULL, NULL);
}

int main() {
  pthread_exit(NULL);
  return 1;
}
$ gcc exit.c -static -lpthread
$ ./a.out
$ echo $?
0
$ objdump -d ./a.out
# .................
409e09:       f0 ff 0d 40 62 29 00    lock decl 0x296240(%rip)        # 6a0050
<__nptl_nthreads>
409e10:       0f 94 c2                sete   %dl
# .................

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