wait_for_proc may fail, and should simply waitpid instead of ptracing

- which means that we need to continue the process after starting it,
  the same as we do when attaching

1 files changed, 11 insertions, 25 deletions

diff --git a/sysdeps/linux-gnu/trace.c b/sysdeps/linux-gnu/trace.c
index 9613271..20c42a8 100644
--- a/sysdeps/linux-gnu/trace.c
+++ b/sysdeps/linux-gnu/trace.c
@@ -108,26 +108,21 @@ trace_me(void)
 }
 
 /* There's a (hopefully) brief period of time after the child process
- * exec's when we can't trace it yet.  Here we wait for kernel to
+ * forks when we can't trace it yet.  Here we wait for kernel to
  * prepare the process.  */
-void
+int
 wait_for_proc(pid_t pid)
 {
-	size_t i;
-	for (i = 0; i < 100; ++i) {
-		/* We read from memory address 0, but that shouldn't
-		 * be a problem: the reading will just fail.  We are
-		 * looking for a particular reason of failure.  */
-		if (ptrace(PTRACE_PEEKTEXT, pid, 0, 0) != -1
-		    || errno != ESRCH)
-			return;
-
-		usleep(1000);
+	/* man ptrace: PTRACE_ATTACH attaches to the process specified
+	   in pid.  The child is sent a SIGSTOP, but will not
+	   necessarily have stopped by the completion of this call;
+	   use wait() to wait for the child to stop. */
+	if (waitpid(pid, NULL, __WALL) != pid) {
+		perror ("trace_pid: waitpid");
+		return -1;
 	}
 
-	fprintf(stderr, "\
-I consistently fail to read a word from the freshly launched process.\n\
-I'll now try to proceed with tracing, but this shouldn't be happening.\n");
+	return 0;
 }
 
 int
@@ -140,16 +135,7 @@ trace_pid(pid_t pid)
 	if (ptrace(PTRACE_ATTACH, pid, 1, 0) < 0)
 		return -1;
 
-	/* man ptrace: PTRACE_ATTACH attaches to the process specified
-	   in pid.  The child is sent a SIGSTOP, but will not
-	   necessarily have stopped by the completion of this call;
-	   use wait() to wait for the child to stop. */
-	if (waitpid (pid, NULL, __WALL) != pid) {
-		perror ("trace_pid: waitpid");
-		return -1;
-	}
-
-	return 0;
+	return wait_for_proc(pid);
 }
 
 void