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#define _GNU_SOURCE
#include <assert.h>
#include <errno.h>
#include <sched.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <sys/wait.h>
#include <unistd.h>
// Based on a test by Steven Stewart-Gallus, see 342040
int fork_routine(void *arg)
{
write(1, "fork_routine\n", 13);
_Exit(EXIT_SUCCESS);
}
int main(void)
{
long page_size = sysconf(_SC_PAGE_SIZE);
assert(page_size != -1);
/* We need an extra page for signals */
long stack_size = sysconf(_SC_THREAD_STACK_MIN) + page_size;
assert(stack_size != -1);
size_t stack_and_guard_size = page_size + stack_size + page_size;
void *child_stack = mmap(
NULL, stack_and_guard_size, PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS | MAP_GROWSDOWN, -1, 0);
if (NULL == child_stack) {
perror("mmap");
return EXIT_FAILURE;
}
/* Guard pages are shared between the stacks */
if (-1 == mprotect((char *)child_stack, page_size, PROT_NONE)) {
perror("mprotect");
return EXIT_FAILURE;
}
if (-1 == mprotect((char *)child_stack + page_size + stack_size,
page_size, PROT_NONE)) {
perror("mprotect");
return EXIT_FAILURE;
}
void *stack_start = (char *)child_stack + page_size + stack_size;
if (0)
printf("stack_start %p page_size %d stack_size %d\n",
stack_start, (int)page_size, (int)stack_size);
write(1, "parent before clone\n", 20);
pid_t child =
clone(fork_routine, stack_start,
SIGCHLD | CLONE_VFORK | CLONE_VM, NULL);
write(1, "parent after clone\n", 19);
if (-1 == child) {
perror("clone");
return EXIT_FAILURE;
}
for (;;) {
int xx;
switch (waitpid(child, &xx, 0)) {
case -1:
switch (errno) {
case EINTR:
continue;
default:
perror("waitpid");
return EXIT_FAILURE;
}
default:
return EXIT_SUCCESS;
}
}
}
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