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base system() on posix_spawn 

this avoids duplicating the fragile logic for executing an external
program without fork.
This commit is contained in:
Rich Felker 2013-02-03 18:21:04 -05:00
parent 4862864fc1
commit a8799356d5
1 changed files with 24 additions and 39 deletions
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63
src/process/system.c
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@ -2,6 +2,7 @@
#include <fcntl.h>
#include <signal.h>
#include <sys/wait.h>
#include <spawn.h>
#include <errno.h>
#include "pthread_impl.h"
#include "libc.h"
@ -12,57 +13,41 @@ static void dummy_0()
weak_alias(dummy_0, __acquire_ptc);
weak_alias(dummy_0, __release_ptc);
pid_t __vfork(void);
void __testcancel(void);
extern char **environ;
int system(const char *cmd)
{
pid_t pid;
sigset_t old;
sigset_t old, reset;
struct sigaction sa = { .sa_handler = SIG_IGN }, oldint, oldquit;
int status = -1, i;
int status = 0x7f00, ret;
posix_spawnattr_t attr;
__testcancel();
pthread_testcancel();
if (!cmd) return 1;
sigaction(SIGINT, &sa, &oldint);
sigaction(SIGQUIT, &sa, &oldquit);
sigprocmask(SIG_BLOCK, SIGALL_SET, &old);
sigaddset(&sa.sa_mask, SIGCHLD);
sigprocmask(SIG_BLOCK, &sa.sa_mask, &old);
__acquire_ptc();
pid = __vfork();
if (pid) __release_ptc();
if (pid > 0) {
sigset_t new = old;
sigaddset(&new, SIGCHLD);
sigprocmask(SIG_BLOCK, &new, 0);
while (waitpid(pid, &status, 0) && errno == EINTR);
}
if (pid) {
sigaction(SIGINT, &oldint, NULL);
sigaction(SIGQUIT, &oldquit, NULL);
sigprocmask(SIG_SETMASK, &old, NULL);
return status;
}
/* Before we can unblock signals in the child, all signal
* handlers must be eliminated -- even implementation-internal
* ones. Otherwise, a signal handler could run in the child
* and clobber the parent's memory (due to vfork). */
for (i=1; i<=8*__SYSCALL_SSLEN; i++) {
struct sigaction sa;
__libc_sigaction(i, 0, &sa);
if (sa.sa_handler!=SIG_IGN && sa.sa_handler!=SIG_DFL) {
sa.sa_handler = SIG_DFL;
__libc_sigaction(i, &sa, 0);
}
}
sigemptyset(&reset);
if (oldint.sa_handler != SIG_IGN) sigaddset(&reset, SIGINT);
if (oldquit.sa_handler != SIG_IGN) sigaddset(&reset, SIGQUIT);
posix_spawnattr_init(&attr);
posix_spawnattr_setsigmask(&attr, &old);
posix_spawnattr_setsigdefault(&attr, &reset);
posix_spawnattr_setflags(&attr, POSIX_SPAWN_SETSIGDEF|POSIX_SPAWN_SETSIGMASK);
ret = posix_spawn(&pid, "/bin/sh", 0, &attr,
(char *[]){"sh", "-c", (char *)cmd, 0}, environ);
posix_spawnattr_destroy(&attr);
if (!ret) while (waitpid(pid, &status, 0)<0 && errno == EINTR);
sigaction(SIGINT, &oldint, NULL);
sigaction(SIGQUIT, &oldquit, NULL);
sigprocmask(SIG_SETMASK, &old, NULL);
execl("/bin/sh", "sh", "-c", cmd, (char *)0);
_exit(127);
if (ret) errno = ret;
return status;
}