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|
/*
* Create NUM_THREADS threads which print "1" and sleep in pause().
* Then create another thread which prints "2", and re-execs the program.
* The leader then either sleeps in pause(), or exits if $LEADER_EXIT is set.
* This triggers "execve'ed thread replaces thread leader" case.
*
* gcc -Wall -Os -o threaded_execve threaded_execve.c
*
* Try running it under strace like this:
*
* # Should not be confused by traced execve-ing thread
* # replacing traced leader:
* strace -oLOG -f ./threaded_execve
*
* # Same, but different output mode. Output after execve
* # should go into leader's LOG.<pid> file, not into execve'ed
* # thread's log file:
* strace -oLOG -ff ./threaded_execve
*
* # Should not be confused by non-traced execve-ing thread
* # replacing traced leader:
* strace -oLOG ./threaded_execve
* ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
* In Linux 3.2, non-traced execve-ing thread does not
* become traced after execve, even though it has pid == leader's pid
* after execve. And yet, strace's waitpid doesn't return ECHILD.
*
* # Run for NUM seconds, not just one second.
* # Watch top to check for memory leaks in strace:
* strace -oLOG -f ./threaded_execve <NUM>
*
*/
#define NUM_THREADS 1
#define _GNU_SOURCE 1
#include <assert.h>
#include <limits.h>
#include <stddef.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <stdio.h>
#include <sched.h>
#include <signal.h>
#include <dirent.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <asm/unistd.h>
/* Define clone2 for all arches */
#ifdef __ia64__
extern int __clone2(int (*fn) (void *), void *child_stack_base,
size_t stack_size, int flags, void *arg, ...);
# define clone2 __clone2
#elif defined(__metag__)
# define clone2(func, stack_base, size, flags, arg...) \
clone(func, stack_base, flags, arg)
#else
# define clone2(func, stack_base, size, flags, arg...) \
clone(func, (stack_base) + (size), flags, arg)
#endif
/* Direct calls to syscalls, avoiding libc wrappers */
#define syscall_tgkill(pid, tid, sig) syscall(__NR_tgkill, (pid), (tid), (sig))
#define syscall_getpid() syscall(__NR_getpid)
#define syscall_gettid() syscall(__NR_gettid)
#define syscall_exit(v) syscall(__NR_exit, (v))
static char my_name[PATH_MAX];
static int leader_final_action;
static int
thread1(void *unused)
{
write(1, "1", 1);
for (;;)
pause();
return 0;
}
static int
thread2(void *unused)
{
char buf[64];
sprintf(buf, "%d", leader_final_action);
write(1, "2", 1);
usleep(20*1000);
/* This fails with ENOENT if leader has exited by now! :) */
execl("/proc/self/exe", "exe", "exe", buf, NULL);
/* So fall back to resolved name */
execl(my_name, "exe", "exe", buf, NULL);
for (;;)
pause();
return 0;
}
static void
thread_leader(void)
{
/* malloc gives sufficiently aligned buffer.
* long buf[] does not! (on ia64).
*/
int cnt = NUM_THREADS;
while (--cnt >= 0) {
/* As seen in pthread_create(): */
clone2(thread1, malloc(16 * 1024), 16 * 1024, 0
| CLONE_VM
| CLONE_FS
| CLONE_FILES | CLONE_SIGHAND | CLONE_THREAD | CLONE_SYSVSEM
| 0 /* no signal to send on death */
, NULL);
usleep(20*1000);
}
clone2(thread2, malloc(16 * 1024), 16 * 1024, 0
| CLONE_VM
| CLONE_FS
| CLONE_FILES | CLONE_SIGHAND | CLONE_THREAD | CLONE_SYSVSEM
| 0 /* no signal to send on death */
, NULL);
/* Various states leader can be while other thread execve's: */
switch (leader_final_action % 3) {
case 0:
syscall_exit(42); /* leader is dead */
case 1:
for (;;)
pause(); /* leader is in syscall */
default:
for (;;)
continue; /* leader is in userspace */
}
}
int
main(int argc, char **argv)
{
if (readlink("/proc/self/exe", my_name, sizeof(my_name)-1) <= 0)
return 1;
setbuf(stdout, NULL);
if (argv[1] && strcmp(argv[1], "exe") == 0) {
leader_final_action = atoi(argv[2]) + 1;
thread_leader();
}
printf("%d: thread leader\n", getpid());
alarm(argv[1] ? atoi(argv[1]) : 1);
thread_leader();
return 0;
}
|
