[patch] Re: [BUG] gdb: quit hangs after step into signal handler

[Jan Kratochvil <jan.kratochvil@redhat.com>]

On Wed, 22 Sep 2010 01:53:56 +0200, Roland McGrath wrote:
> Even if you were paranoid about some old kernel where PTRACE_KILL might work
> better (dubious if there are any such, but that's why it's paranoia), you
> could do this before PTRACE_KILL and it should certainly be fine everywhere.

Problem is the inferior will start running after PTRACE_KILL.  Current GDB:

Quit anyway? (y or n) y
<hang by sleep (600);>

read(0, "y\n", 1024)                    = 2
ptrace(PTRACE_KILL, 32336, 0, 0)        = 0
wait4(32336,

Before kill (SIGKILL) gets applied the code may do something unexpected.
Why do you consider SIGKILL first, PTRACE_KILL second as worse?

(Probably not so important now.)


Thanks,
Jan


gdb/
2011-02-23  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* linux-nat.c (kill_callback): Use SIGKILL first.

gdb/testsuite/
2011-02-23  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* gdb.base/kill-after-signal.c: New file.
	* gdb.base/kill-after-signal.exp: New file.

--- a/gdb/linux-nat.c
+++ b/gdb/linux-nat.c
@@ -3802,6 +3802,18 @@ linux_nat_wait (struct target_ops *ops,
 static int
 kill_callback (struct lwp_info *lp, void *data)
 {
+  /* PTRACE_KILL may resume the inferior.  Send SIGKILL first.  */
+
+  errno = 0;
+  kill (GET_LWP (lp->ptid), SIGKILL);
+  if (debug_linux_nat)
+    fprintf_unfiltered (gdb_stdlog,
+			"KC:  kill (SIGKILL) %s, 0, 0 (%s)\n",
+			target_pid_to_str (lp->ptid),
+			errno ? safe_strerror (errno) : "OK");
+
+  /* Some kernels ignore even SIGKILL for processes under ptrace.  */
+
   errno = 0;
   ptrace (PTRACE_KILL, GET_LWP (lp->ptid), 0, 0);
   if (debug_linux_nat)
--- /dev/null
+++ b/gdb/testsuite/gdb.base/kill-after-signal.c
@@ -0,0 +1,37 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2011 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include <signal.h>
+#include <assert.h>
+#include <unistd.h>
+#include <stdio.h>
+
+void
+handler (int signo)
+{
+  sleep (600);
+  assert (0);
+}
+
+int
+main (void)
+{
+  signal (SIGUSR1, handler);
+  raise (SIGUSR1);
+  assert (0);
+  return 0;
+}
--- /dev/null
+++ b/gdb/testsuite/gdb.base/kill-after-signal.exp
@@ -0,0 +1,29 @@
+# Copyright (C) 2011 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+set testfile "kill-after-signal"
+if [prepare_for_testing ${testfile}.exp ${testfile}] {
+    return -1
+}
+
+gdb_test "handle SIGUSR1 stop print pass" "SIGUSR1\[ \t\]+Yes\[ \t\]+Yes\[ \t\]+Yes\[ \t\]+.*"
+
+if ![runto_main] {
+    return -1
+}
+
+gdb_test "continue" "Program received signal SIGUSR1, .*"
+gdb_test "stepi" "\r\nhandler .*"
+gdb_test "kill" "^y" "kill" "Kill the program being debugged\\? \\(y or n\\) $" "y"