[RFC][PATCH v2 2/2][PR gdb/24069] [fix] Skip over WIFSTOPPED wait4 status

[Philippe Blain via Gdb-patches <gdb-patches@sourceware.org>]

From: Dominique Quatravaux <dominique.quatravaux@epfl.ch>

On modern Darwin's, there appears to be a new circumstance in which a
MACH_NOTIFY_DEAD_NAME message can be received, and which was not
previously accounted for: to signal the WIFSTOPPED condition in the
debuggee. In that case the debuggee is not dead yet (and in fact,
counting it as dead would cause a zombie leak - A process in such a
state reparents to PID 1, but cannot be killed).

- Read and ignore such messages (counting on the next exception
message to let us know of the inferior's new state again)
- Refactor logging so as to clearly distinguish between the three
MACH_NOTIFY_DEAD_NAME cases (WIFEXITED, WIFSTOPPED, signal)

Co-authored-by: Louis-He <1726110778@qq.com>
Co-authored-by: Philippe Blain <levraiphilippeblain@gmail.com>

ChangeLog:

2022-02-05  Dominique Quatravaux <dominique.quatravaux@epfl.ch>

	PR gdb/24609
	* gdb/darwin-nat.c (darwin_nat_target::decode_message): Also
	check for WIFSTOPPED upon MACH_NOTIFY_DEAD_NAME.
---

Notes:
    I hope I did not mess up the indentation here. I did not find any guidelines
    about tab width in the C/C++ coding standards [1].
    
    [1] https://sourceware.org/gdb/wiki/Internals%20GDB-C-Coding-Standards#Whitespaces

 gdb/darwin-nat.c | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/gdb/darwin-nat.c b/gdb/darwin-nat.c
index 8b0ecfd5b77..a3c6a978676 100644
--- a/gdb/darwin-nat.c
+++ b/gdb/darwin-nat.c
@@ -1063,7 +1063,7 @@ darwin_nat_target::decode_message (mach_msg_header_t *hdr,
     }
   else if (hdr->msgh_id == 0x48)
     {
-      /* MACH_NOTIFY_DEAD_NAME: notification for exit.  */
+      /* MACH_NOTIFY_DEAD_NAME: notification for exit *or* WIFSTOPPED. */
       int res;
 
       res = darwin_decode_notify_message (hdr, &inf);
@@ -1103,16 +1103,26 @@ darwin_nat_target::decode_message (mach_msg_header_t *hdr,
 		  return minus_one_ptid;
 		}
 	      if (WIFEXITED (wstatus))
-		status->set_exited (WEXITSTATUS (wstatus));
+		{
+		  status->set_exited (WEXITSTATUS (wstatus));
+	          inferior_debug (4, _("darwin_wait: pid=%d exit, status=0x%x\n"),
+				  res_pid, wstatus);
+		}
+	      else if (WIFSTOPPED (wstatus))
+		{
+		  status->set_ignore ();
+		  inferior_debug (4, _("darwin_wait: pid %d received WIFSTOPPED\n"),
+				  res_pid);
+		  return minus_one_ptid;
+		}
 	      else
 		{
 		  status->set_signalled
 		    (gdb_signal_from_host (WTERMSIG (wstatus)));
+		  inferior_debug (4, _("darwin_wait: pid=%d received signal %d\n"),
+				  res_pid, status->sig());
 		}
 
-	      inferior_debug (4, _("darwin_wait: pid=%d exit, status=0x%x\n"),
-			      res_pid, wstatus);
-
 	      return ptid_t (inf->pid);
 	    }
 	  else
-- 
2.29.2