libstdc++/4372: #pragma weak pthread* inclusion causes applications to crash without a linker error when one forgets to link with -lpthread

[carlo at alinoe dot com]

>Number:         4372
>Category:       libstdc++
>Synopsis:       #pragma weak pthread* inclusion causes applications to crash without a linker error when one forgets to link with -lpthread
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          wrong-code
>Submitter-Id:   net
>Arrival-Date:   Thu Sep 20 17:26:00 PDT 2001
>Closed-Date:
>Last-Modified:
>Originator:     Carlo Wood
>Release:        3.0.1
>Organization:
>Environment:
i686-rawhide-gnu-linux
>Description:
Recently my (test) application started to core dump in
__libc_strtol_internal (according to gdb), apparently
called from pthread_getspecific.

It took me awhile to find out that I had forgotten
to add a -lpthread when linking.  I considered it a bug
that the linker didn't give an error so I tried to write
a small test case to reproduce this, but in the test case
the linker DID give me `undefined reference to pthread_getspecific'...

After a little investigation, I found that the difference
between the test case and the problem case could be brought
back to the *.ii file: the problem case has included a
series of #pragma weak pthread... that caused the linker
to think that these functions are present as local functions,
while actually it causes a call to address 0x0 (hence the
`__libc_strtol_internal' I guess).

Because I can not succeed to make a small test case, I'll
give results of the my own investigation using the large
problem case:

~/c++/libcw_branch-threading/src/libcwd/tests>g++-3.0.1 -DHAVE_CONFIG_H -I. -I- -I../include -DCWDEBUG -g -D_REENTRANT -c hello_world.cc -save-temps -v
Reading specs from /usr/local/gcc-3.0.1/lib/gcc-lib/i686-pc-linux-gnu/3.0.1/specs
Configured with: /usr/src/gcc/gcc-3.0.1/configure --prefix=/usr/local/gcc-3.0.1 --enable-shared --with-gnu-as --with-gnu-ld --enable-languages=c++ --enable-debug --enable-threads
Thread model: posix
gcc version 3.0.1
 /usr/local/gcc-3.0.1/lib/gcc-lib/i686-pc-linux-gnu/3.0.1/cpp0 -lang-c++ -D__GNUG__=3 -D__GXX_DEPRECATED -D__EXCEPTIONS -D__GXX_ABI_VERSION=100 -v -I. -I- -I../include -D__GNUC__=3 -D__GNUC_MINOR__=0 -D__GNUC_PATCHLEVEL__=1 -D__ELF__ -Dunix -Dlinux -D__ELF__ -D__unix__ -D__linux__ -D__unix -D__linux -Asystem=posix -D__NO_INLINE__ -D__STDC_HOSTED__=1 -D_GNU_SOURCE -Acpu=i386 -Amachine=i386 -Di386 -D__i386 -D__i386__ -D__tune_i686__ -D__tune_pentiumpro__ -DHAVE_CONFIG_H -DCWDEBUG -D_REENTRANT hello_world.cc hello_world.ii
GNU CPP version 3.0.1 (cpplib) (i386 Linux/ELF)
ignoring nonexistent directory "/usr/local/gcc-3.0.1/i686-pc-linux-gnu/include"
#include "..." search starts here:
 .
#include <...> search starts here:
 ../include
 /usr/local/gcc-3.0.1/include/g++-v3
 /usr/local/gcc-3.0.1/include/g++-v3/i686-pc-linux-gnu
 /usr/local/gcc-3.0.1/include/g++-v3/backward
 /usr/local/include
 /usr/local/gcc-3.0.1/lib/gcc-lib/i686-pc-linux-gnu/3.0.1/include
 /usr/include
End of search list.
 /usr/local/gcc-3.0.1/lib/gcc-lib/i686-pc-linux-gnu/3.0.1/cc1plus -fpreprocessed hello_world.ii -quiet -dumpbase hello_world.cc -g -version -o hello_world.s
GNU CPP version 3.0.1 (cpplib) (i386 Linux/ELF)
GNU C++ version 3.0.1 (i686-pc-linux-gnu)
        compiled by GNU C version 3.0.1.
 as --traditional-format -V -Qy -o hello_world.o hello_world.s
GNU assembler version 2.11.90.0.8 (i386-redhat-linux) using BFD version 2.11.90.0.8

Next I edit the *.ii file and remove the #pragma weak lines,
showing that these are the problem:

~/c++/libcw_branch-threading/src/libcwd/tests>vi hello_world.ii
~/c++/libding/src/libcwd/tests>/usr/local/gcc-3.0.1/lib/gcc-lib/i686-pc-linux-gnu/3.0.1/cc1plus -fpreprocessed hello_world.ii -quiet -dumpbase hello_world.cc -g -version -o hello_world.s
GNU CPP version 3.0.1 (cpplib) (i386 Linux/ELF)
GNU C++ version 3.0.1 (i686-pc-linux-gnu)
        compiled by GNU C version 3.0.1.
~/c++/libcw_branch-threading/src/libcwd/tests>as --traditional-format -V -Qy -o hello_world.o hello_world.s
GNU assembler version 2.11.90.0.8 (i386-redhat-linux) using BFD version 2.11.90.0.8
~/c++/libcw_branch-threading/src/libcwd/tests>nm hello_world.o | grep pthread
00000330 t _Z20__gthread_mutex_lockP15pthread_mutex_t
00000360 t _Z22__gthread_mutex_unlockP15pthread_mutex_t
         U pthread_create
         U pthread_getspecific
         U pthread_key_create
         U pthread_mutex_lock
         U pthread_mutex_unlock
         U pthread_once
         U pthread_setspecific

Next, I do this again but now change a pragma into
#xxxpragma, getting:

~/c++/libcw_branch-threading/src/libcwd/tests>vi hello_world.ii
~/c++/libcw_branch-threading/src/libcwd/tests>/usr/local/gcc-3.0.1/lib/gcc-lib/i686-pc-linux-gnu/3.0.1/cc1plus -fpreprocessed hello_world.ii -quiet -dumpbase hello_world.cc -g -version -o hello_world.s
GNU CPP version 3.0.1 (cpplib) (i386 Linux/ELF)
GNU C++ version 3.0.1 (i686-pc-linux-gnu)
        compiled by GNU C version 3.0.1.
In file included from /usr/local/gcc-3.0.1/include/g++-v3/i686-pc-linux-gnu/bits/gthr.h:98,
                 from /usr/local/gcc-3.0.1/include/g++-v3/i686-pc-linux-gnu/bits/c++io.h:37,
                 from /usr/local/gcc-3.0.1/include/g++-v3/bits/fpos.h:39,
                 from /usr/local/gcc-3.0.1/include/g++-v3/bits/std_iosfwd.h:41,
                 from /usr/local/gcc-3.0.1/include/g++-v3/bits/std_ios.h:39,
                 from /usr/local/gcc-3.0.1/include/g++-v3/bits/std_ostream.h:39,
                 from /usr/local/gcc-3.0.1/include/g++-v3/bits/std_iostream.h:40,
                 from /usr/local/gcc-3.0.1/include/g++-v3/iostream:31,
                 from ../include/libcw/debug.h:81,
                 from hello_world_debug.h:18,
                 from hello_world.cc:28:
/usr/local/gcc-3.0.1/include/g++-v3/i686-pc-linux-gnu/bits/gthr-default.h:48:2: invalid preprocessing directive #xxxpragma

Apparently, the pragma's are in bits/gthr-default.h:48.

Hmm, maybe I can reproduce this after all by including
#include <iosfwd> in the small test case...

~>g++-3.0.1 test.cc -o test
~>./test
Segmentation fault (core dumped)

Yup, that does the trick.

I think this is highly annoying.  The #pragma weak
should not make the linker think the function exists :/.


>How-To-Repeat:
Compile the following code snippet and don't link with
-lpthread (no error occurs):

#include <iosfwd>
#include <pthread.h>
 
static pthread_once_t S_key_once;
static pthread_key_t S_key;
 
void S_destroy(void* tsd_ptr) throw()
{
}
 
void S_alloc_key(void) throw()
{
  pthread_key_create(&S_key, S_destroy);
}
 
int main(void)
{
  pthread_once(&S_key_once, S_alloc_key);
}
>Fix:
Link with -lpthread
>Release-Note:
>Audit-Trail:
>Unformatted: