proc: bugfix: proc.Launch race (OS X)

proc/exec_darwin.c

@@ -15,6 +15,12 @@ fork_exec(char *argv0, char **argv, int size,
 	int fd[2];
 	if (pipe(fd) < 0) return -1;
 
+       // Create another pipe so that we know when we're about to exec. This ensures that control only returns
+       // back to Go-land when we call exec, effectively eliminating a race condition between launching the new
+       // process and trying to read its memory.
+       int wfd[2];
+       if (pipe(wfd) < 0) return -1;
+
 	kern_return_t kret;
 	pid_t pid = fork();
 	if (pid > 0) {
@@ -26,6 +32,11 @@ fork_exec(char *argv0, char **argv, int size,
 		char msg = 'c';
 		write(fd[1], &msg, 1);
 		close(fd[1]);
+
+               char w;
+               read(wfd[0], &w, 1);
+               close(wfd[0]);
+
 		return pid;
 	}
 
@@ -53,6 +64,10 @@ fork_exec(char *argv0, char **argv, int size,
 	pret = ptrace(PT_SIGEXC, 0, 0, 0);
 	if (pret != 0 && errno != 0) return -errno;
 
+	char msg = 'd';
+	write(wfd[1], &msg, 1);
+	close(wfd[1]);
+
 	// Create the child process.
 	execve(argv0, argv, environ);
 

proc/proc.go

@@ -743,6 +743,10 @@ func (dbp *Process) getGoInformation() (ver GoVersion, isextld bool, err error)
 		err = fmt.Errorf("Could not determine version number: %v\n", err)
 		return
 	}
+	if vv.Unreadable != nil {
+		err = fmt.Errorf("Unreadable version number: %v\n", vv.Unreadable)
+		return
+	}
 
 	ver, ok := parseVersionString(constant.StringVal(vv.Value))
 	if !ok {

proc/proc_darwin.go

@@ -78,7 +78,7 @@ func Launch(cmd []string) (*Process, error) {
 	if err != nil {
 		return nil, err
 	}
-	err = dbp.Continue()
+	err = dbp.continueOnce()
 	return dbp, err
 }