Re: [patch] Fix Linux attach to signalled/stopped processes

[Pedro Alves <pedro@codesourcery.com>]

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A Saturday 12 April 2008 00:21:33, Pedro Alves wrote:
> A Friday 11 April 2008 23:54:48, Pedro Alves wrote:
> > A Friday 11 April 2008 23:19:58, Daniel Jacobowitz wrote:
> > > Any idea how to do this?
> >

> Actually, get_last_target_status should give you the ptid
> you want, I think.

Like so ?

The only way I could find to pass args != NULL, was to
attach, and then "quit $signo".

"detach $SIGNO" doesn't work:

(gdb) detach 21
Undefined detach command: "21".  Try "help detach".

-- and was glad it didn't.  I'm was hoping we can use
"detach $pid" in the future, to mirror "attach $pid",
but now I'm not sure we can...

Anyway, "q 19" did send a SIGSTOP, and the process
was stopped.

And I was able to attach to stopped processes, and
the new tests passed, which is nice.  Hurray!

-- 
Pedro Alves

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2008-04-12  Pedro Alves  <pedro@codesourcery.com>

	* linux-nat.c (get_pending_status): New.
	(detach_callback): Pass pending signal.
	(linux_nat_detach): Pass pending signal.

---
 gdb/linux-nat.c |   50 ++++++++++++++++++++++++++++++++++++++++----------
 1 file changed, 40 insertions(+), 10 deletions(-)

Index: src/gdb/linux-nat.c
===================================================================
--- src.orig/gdb/linux-nat.c	2008-04-12 16:20:27.000000000 +0100
+++ src/gdb/linux-nat.c	2008-04-12 17:36:54.000000000 +0100
@@ -1289,6 +1289,36 @@ linux_nat_attach (char *args, int from_t
     }
 }
 
+/* Get pending status of LP.  */
+static int
+get_pending_status (struct lwp_info *lp, int *status)
+{
+  struct target_waitstatus last;
+  ptid_t last_ptid;
+
+  get_last_target_status (&last_ptid, &last);
+
+  /* If this lwp is the ptid that GDB is processing an event from, the
+     signal will be in stop_signal.  Otherwise, in all-stop + sync
+     mode, we may cache pending events in lp->status while trying to
+     stop all threads (see stop_wait_callback).  In async mode, the
+     events are always cached in waitpid_queue.  */
+
+  *status = 0;
+  if (GET_LWP (lp->ptid) == GET_LWP (last_ptid))
+    {
+      if (stop_signal != TARGET_SIGNAL_0
+	  && signal_pass_state (stop_signal))
+	*status = W_STOPCODE (target_signal_to_host (stop_signal));
+    }
+  else if (target_can_async_p ())
+    queued_waitpid (GET_LWP (lp->ptid), status, __WALL);
+  else
+    *status = lp->status;
+
+  return 0;
+}
+
 static int
 detach_callback (struct lwp_info *lp, void *data)
 {
@@ -1311,18 +1341,18 @@ detach_callback (struct lwp_info *lp, vo
       lp->signalled = 0;
     }
 
-  /* Pass on the last signal, if appropriate.  */
-  if (lp->status == 0 && GET_LWP (lp->ptid) == GET_LWP (inferior_ptid)
-      && stop_signal != TARGET_SIGNAL_0 && signal_pass_state (stop_signal))
-    lp->status = W_STOPCODE (target_signal_to_host (stop_signal));
-
   /* We don't actually detach from the LWP that has an id equal to the
      overall process id just yet.  */
   if (GET_LWP (lp->ptid) != GET_PID (lp->ptid))
     {
+      int status = 0;
+
+      /* Pass on any pending signal for this LWP.  */
+      get_pending_status (lwp_list, &status);
+
       errno = 0;
       if (ptrace (PTRACE_DETACH, GET_LWP (lp->ptid), 0,
-		  WSTOPSIG (lp->status)) < 0)
+		  WSTOPSIG (status)) < 0)
 	error (_("Can't detach %s: %s"), target_pid_to_str (lp->ptid),
 	       safe_strerror (errno));
 
@@ -1332,7 +1362,6 @@ detach_callback (struct lwp_info *lp, vo
 			    target_pid_to_str (lp->ptid),
 			    strsignal (WSTOPSIG (lp->status)));
 
-      drain_queued_events (GET_LWP (lp->ptid));
       delete_lwp (lp->ptid);
     }
 
@@ -1349,14 +1378,15 @@ linux_nat_detach (char *args, int from_t
   if (target_can_async_p ())
     linux_nat_async (NULL, 0);
 
-  iterate_over_lwps (detach_callback, &status);
+  iterate_over_lwps (detach_callback, NULL);
 
   /* Only the initial process should be left right now.  */
   gdb_assert (num_lwps == 1);
 
   /* Pass on any pending signal for the last LWP.  */
-  status = lwp_list->status;
-  if (WIFSTOPPED (status) && (args == NULL || *args == '\0'))
+  if ((args == NULL || *args == '\0')
+      && get_pending_status (lwp_list, &status) != -1
+      && WIFSTOPPED (status))
     {
       args = alloca (8);
       sprintf (args, "%d", (int) WSTOPSIG (status));