Subject: bug#33154: 27.0.50; create_process on Darwin should not invoke setsid() after vfork() [PATCH]

From: Filipp Gunbin <[email-masked]>
Date: Thu, 25 Oct 2018 22:30:12 +0300

This resulted from analysis of bug 33050.  To avoid repetition, here's
the message with explanation:
http://lists.gnu.org/archive/html/bug-gnu-emacs/2018-10/msg00763.html

Suggested patch is below.

Thanks.

In GNU Emacs 27.0.50 (build 12, x86_64-apple-darwin17.7.0, NS appkit-1561.60 Version 10.13.6 (Build 17G65))
 of 2018-10-25 built on fgunbin.playteam.ru
Repository revision: f1f1687fcd8d48cd519c0f2977bcecbf394a7f01
System Description:  Mac OS X 10.13.6

diff --git a/src/process.c b/src/process.c
index 6cda4f27ac..1f8810927d 100644
--- a/src/process.c
+++ b/src/process.c
@@ -2066,21 +2066,7 @@ create_process (Lisp_Object process, char **new_argv, Lisp_Object current_dir)
   int volatile forkerr_volatile = forkerr;
   struct Lisp_Process *p_volatile = p;
 
-#ifdef DARWIN_OS
-  /* Darwin doesn't let us run setsid after a vfork, so use fork when
-     necessary.  Also, reset SIGCHLD handling after a vfork, as
-     apparently macOS can mistakenly deliver SIGCHLD to the child.  */
-  if (pty_flag)
-    pid = fork ();
-  else
-    {
-      pid = vfork ();
-      if (pid == 0)
-	signal (SIGCHLD, SIG_DFL);
-    }
-#else
   pid = vfork ();
-#endif
 
   current_dir = current_dir_volatile;
   lisp_pty_name = lisp_pty_name_volatile;
@@ -2091,15 +2077,35 @@ create_process (Lisp_Object process, char **new_argv, Lisp_Object current_dir)
   p = p_volatile;
 
   pty_flag = p->pty_flag;
-
   if (pid == 0)
 #endif /* not WINDOWSNT */
     {
+#ifdef DARWIN_OS
+      /* Work around a macOS bug, where SIGCHLD is apparently
+	 delivered to a vforked child instead of to its parent.  See:
+	 https://lists.gnu.org/r/emacs-devel/2017-05/msg00342.html
+      */
+      signal (SIGCHLD, SIG_DFL);
+#endif
+
       /* Make the pty be the controlling terminal of the process.  */
 #ifdef HAVE_PTYS
       /* First, disconnect its current controlling terminal.
 	 Do this even if !PTY_FLAG; see Bug#30762.  */
+#ifdef DARWIN_OS
+      /* Darwin doesn't let us run setsid after a vfork, so use
+         TIOCNOTTY when necessary. */
+      {
+	int j = emacs_open (DEV_TTY, O_RDWR, 0);
+	if (j >= 0)
+	  {
+	    ioctl (j, TIOCNOTTY, 0);
+	    emacs_close (j);
+	  }
+      }
+#else
       setsid ();
+#endif
       /* Make the pty's terminal the controlling terminal.  */
       if (pty_flag && forkin >= 0)
 	{