1 #define _GNU_SOURCE
2 #include <assert.h>
3 #include <errno.h>
4 #include <sched.h>
5 #include <stdio.h>
6 #include <stdlib.h>
7 #include <sys/mman.h>
8 #include <sys/wait.h>
9 #include <unistd.h>
10 // Based on a test by Steven Stewart-Gallus, see 342040
fork_routine(void * arg)11 int fork_routine(void *arg)
12 {
13 write(1, "fork_routine\n", 13);
14 _Exit(EXIT_SUCCESS);
15 }
16
main(void)17 int main(void)
18 {
19 long page_size = sysconf(_SC_PAGE_SIZE);
20 assert(page_size != -1);
21
22 /* We need an extra page for signals */
23 long stack_size = sysconf(_SC_THREAD_STACK_MIN) + page_size;
24 assert(stack_size != -1);
25
26 size_t stack_and_guard_size = page_size + stack_size + page_size;
27 void *child_stack = mmap(
28 NULL, stack_and_guard_size, PROT_READ | PROT_WRITE,
29 MAP_PRIVATE | MAP_ANONYMOUS | MAP_GROWSDOWN, -1, 0);
30 if (NULL == child_stack) {
31 perror("mmap");
32 return EXIT_FAILURE;
33 }
34
35 /* Guard pages are shared between the stacks */
36 if (-1 == mprotect((char *)child_stack, page_size, PROT_NONE)) {
37 perror("mprotect");
38 return EXIT_FAILURE;
39 }
40
41 if (-1 == mprotect((char *)child_stack + page_size + stack_size,
42 page_size, PROT_NONE)) {
43 perror("mprotect");
44 return EXIT_FAILURE;
45 }
46
47 void *stack_start = (char *)child_stack + page_size + stack_size;
48 if (0)
49 printf("stack_start %p page_size %d stack_size %d\n",
50 stack_start, (int)page_size, (int)stack_size);
51 write(1, "parent before clone\n", 20);
52 pid_t child =
53 clone(fork_routine, stack_start,
54 SIGCHLD | CLONE_VFORK | CLONE_VM, NULL);
55 write(1, "parent after clone\n", 19);
56 if (-1 == child) {
57 perror("clone");
58 return EXIT_FAILURE;
59 }
60
61 for (;;) {
62 int xx;
63 switch (waitpid(child, &xx, 0)) {
64 case -1:
65 switch (errno) {
66 case EINTR:
67 continue;
68 default:
69 perror("waitpid");
70 return EXIT_FAILURE;
71 }
72
73 default:
74 return EXIT_SUCCESS;
75 }
76 }
77 }
78