base system() on posix_spawn

this avoids duplicating the fragile logic for executing an external
program without fork.

src/process/system.c

@@ -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);
-
-	__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);
-		}
-	}
-
+	sigaddset(&sa.sa_mask, SIGCHLD);
+	sigprocmask(SIG_BLOCK, &sa.sa_mask, &old);
+
+	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;
 }