Problems with clone and gcc

Problems with clone and gcc

[J.A. Magallon]

Hi all.

I write this here to see if you can give me some clue on a strange behaviour
with the clone system call. Really I want a hint about if it is a kernel
issue, a glibc(pthreads) one or a gcc issue. If sometimes it works looks
like not a kernel issue, but who knows...

Abstract: compiling a program with 'gcc -pthread' or just linking with
-lpthread (even if I just do not call any pthread_xxx), makes the
'clone()' call (glibc) fail. It does not jump to the given function.
Checked on both:
gcc (GCC) 3.1.1 (Mandrake Linux 8.3 3.1.1-0.4mdk)
gcc version 2.96 20000731 (Mandrake Linux 8.2 2.96-0.76mdk)

Sample test:

#include <sched.h>
#include <signal.h>
#include <stdio.h>

#define STSZ (4*1024)

int pslave(void *data);

int main(int argc,char** argv)
{
	int		tid;
	char*	stack;

	stack = (char*)valloc(STSZ);
	puts("about to clone...");
	tid = clone(pslave,stack+STSZ-1,CLONE_VM|SIGCHLD,0);
	if (tid<0)
	{
		perror("clone");
		exit(1);
	}
	puts("clone ok");

	wait(0);

	free(stack);

	return 0;
}

int pslave(void *data)
{
	puts("slave running");
	sleep(1);
	puts("slave done");

	return 0;
}


-- 
J.A. Magallon             \   Software is like sex: It's better when it's free
mailto:jamagallon@able.es  \                    -- Linus Torvalds, FSF T-shirt
Linux werewolf 2.4.19-pre10-jam3, Mandrake Linux 8.3 (Cooker) for i586
gcc (GCC) 3.1.1 (Mandrake Linux 8.3 3.1.1-0.4mdk)