Date: Wed, 19 Aug 1998 12:16:21 -0400 (EDT) From: Luoqi Chen <luoqi@watermarkgroup.com> To: bright@www.hotjobs.com, hackers@FreeBSD.ORG Subject: Re: sfork()? Message-ID: <199808191616.MAA06764@lor.watermarkgroup.com>
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You need to set up separate stack for the child, this cannot be done
without any assembly. We need a wrapper function for rfork() in libc.
Below is a small test program I wrote a while ago, you may adapt it
to your needs if you want. -lq
#include <sys/syscall.h>
#include <stdio.h>
#include <unistd.h>
void
callfunc(int (*func)(void *), void *arg)
{
_exit((*func)(arg));
}
int
rforkcall(void *stack, void *func, void *arg)
{
register int *sp = (int *)stack;
*--sp = (int)arg;
*--sp = (int)func;
*--sp = 0;
*--sp = (int)callfunc;
__asm__(
"pushl %2;\n\t"
"pushl $0;\n\t"
"movl %1,%%eax;\n\t"
".byte 0x9a; .long 0; .word 7;\n\t"
"cmpl $0, %%edx; je 1f;\n\t"
"movl %0,%%esp; ret;\n1:\n\t"
"addl $8,%%esp" :
: "r" (sp), "g" (SYS_rfork), "g" (RFPROC|RFMEM)
: "eax", "edx");
}
int n = 0;
int a(char *s)
{
fprintf(stderr, "%s %d\n", s, n++);
return 0;
}
char stack1[4096];
char stack2[4096];
main()
{
rforkcall(stack1+4096, (void *)a, "thread");
rforkcall(stack2+4096, (void *)a, "thread");
a("main");
}
> can someone explain why this doesn't work?
>
> (the child process just segfaults, even without the printfs)
>
> ----- CUT
>
> #include <stdio.h>
> #include <unistd.h>
>
> volatile int t=0;
>
> int main(void){
>
> pid_t pid;
>
> if(pid = rfork(RFPROC | RFMEM)){
> printf("(parent)pid = %d\n",pid);
> while(1){
> printf("%d\n",t);
> sleep(1);
> }
> } else {
> printf("doesn't die here...");
> t = 1;
> printf("changed t... ");
> sleep(10000);
> }
>
> printf("pid = %d about to exit\n",pid);
> return(0);
> }
>
> ----- END
>
>
> Alfred Perlstein - Programmer, HotJobs Inc. - www.hotjobs.com
> -- There are operating systems, and then there's BSD.
> -- http://www.freebsd.org/
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