dietlibc (0.31), fork and pthreads

Hi,


I stumbled across a strange behaviour when linking pthreads in a program that 
forks and creates a pipe. It looks like after fork()ing, in the child 
process, stdin is closed - but *only* when pthreads is linked in (it doesn't 
even need to be actually used). I don't know if this is a dietlibc thing, but 
maybe someone of you has an idea... 

(by the way, I wanted to check if in 0.32 the behaviour is the same, but 0.32 
segfaults on my machine; this, however, is another problem I'd like not to 
mix in this mail :-) so, if the behaviour I described here is fixed in 0.32 
or trunk, please tell me so, then I'll try and get it running - maybe with 
help of this list as well.)

Back to my current issue.

The little test case I use:
------------------------------------------------------------------------
$ cat forktest.c
#include <stdio.h>
#include <sys/types.h>

int main(int argc, char **argv) {
        int fds[2] = {0};
        pipe(fds);
        printf("%s:%d [%s] - pipe() returned %d,%d\n", __FILE__,
		__LINE__, "before fork", fds[0], fds[1]);
        close(fds[0]);
        close(fds[1]);

        pid_t pid = fork();
        if (pid == 0) {
                pipe(fds);
                printf("%s:%d [%s] - pipe() returned %d,%d\n", __FILE__,
			__LINE__, "child", fds[0], fds[1]);
                close(fds[0]);
                close(fds[1]);
        }
        else {
                pipe(fds);
                printf("%s:%d [%s] - pipe() returned %d,%d\n", __FILE__,
			__LINE__, "parent", fds[0], fds[1]);
                close(fds[0]);
                close(fds[1]);

                waitpid(pid);
        }

        return 0;
}
------------------------------------------------------------------------

Now I'm compiling this test-program with gcc, against glibc, dietlibc, both 
with linking pthreads in and without. Note, again, that nothing of pthreads 
is actually used in that test program...

$ gcc -o forktest_gcc_pure forktest.c
$ gcc -o forktest_gcc_pthreads forktest.c -lpthread
$ diet gcc -o forktest_diet_pure forktest.c
$ diet gcc -o forktest_diet_pthreads forktest.c -lpthread

Now, when running those test programs, I'd expect the pipes to use fds 3 and 4 
(because pipe() uses the lowest two free fds). Surprisingly, the output looks 
like this:

$ ./forktest_gcc_pure
forktest.c:8 [before fork] - pipe() returned 3,4
forktest.c:15 [child] - pipe() returned 3,4
forktest.c:21 [parent] - pipe() returned 3,4

$ ./forktest_gcc_pthreads
forktest.c:8 [before fork] - pipe() returned 3,4
forktest.c:15 [child] - pipe() returned 3,4
forktest.c:21 [parent] - pipe() returned 3,4

$ ./forktest_diet_pure
forktest.c:8 [before fork] - pipe() returned 3,4
forktest.c:15 [child] - pipe() returned 3,4
forktest.c:21 [parent] - pipe() returned 3,4

$ ./forktest_diet_pthreads
forktest.c:8 [before fork] - pipe() returned 3,4
forktest.c:15 [child] - pipe() returned 0,3
forktest.c:21 [parent] - pipe() returned 3,4


...so only the combination -lpthreads and dietlibc causes fd 0 to be used by 
the pipe, only in the child after forking. fd 0 seems to be somehow closed by 
fork()...


Has someone an idea?


Thanks,
  Tim


-- 
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<>                                                              <>
<> Tim München, M.Sc.        [email protected]   <>
<> Bergische Universitaet                                       <>
<> FB C - Physik             Tel.: +49 (0)202 439-3521          <>
<> Gaussstr. 20              Fax : +49 (0)202 439-2811          <>
<> 42097 Wuppertal                                              <>
<>                                                              <>
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