Fix a multi-threaded/process exec in non-stop mode bug.

[Pedro Alves <pedro at codesourcery dot com>]

I've checked this in.

gdb/
2009-05-27  Pedro Alves  <pedro@codesourcery.com>

	* infrun.c (follow_exec): Clear the stop_requested flag.
	* linux-nat.c (linux_handle_extended_wait) <PTRACE_EVENT_EXEC>:
	Add debug output.

gdb/testsuite/
2009-05-27  Pedro Alves  <pedro@codesourcery.com>

	* gdb.mi/nsthrexec.c, gdb.mi/mi-nsthrexec.exp: New.

Basically, an exec event is of a rare kind.  Most (all?) other stop
events that can only happen in running->stopped transitions,
but, it turns out that an exec event can be reported even
if the thread that gets the event was already stopped before.

Here's the failure mode:

 >./gdb -ex "set target-async 1" -ex "set non-stop 1" ./testsuite/gdb.mi/mi-nsthrexec
 (gdb) b thread_execler
 Breakpoint 1 at 0x400654: file ../../../src/gdb/testsuite/gdb.mi/nsthrexec.c, line 28.
 (gdb) r&
 Starting program: /home/pedro/gdb/sspaces/build-all/gdb/testsuite/gdb.mi/mi-nsthrexec
 (gdb) [Thread debugging using libthread_db enabled]
 [New Thread 0x40800950 (LWP 30972)]

 Breakpoint 1, thread_execler (arg=0x0) at ../../../src/gdb/testsuite/gdb.mi/nsthrexec.c:28
 28        if (execl (image, image, NULL) == -1)
 interrupt
 (gdb)
 [Thread 0x7ffff7fd66e0 (LWP 30969)] #1 stopped.
 0x00007ffff7bcb796 in pthread_join () from /lib/libpthread.so.0
 info threads
   2 Thread 0x40800950 (LWP 30972)  thread_execler (arg=0x0) at ../../../src/gdb/testsuite/gdb.mi/nsthrexec.c:28
 * 1 Thread 0x7ffff7fd66e0 (LWP 30969)  0x00007ffff7bcb796 in pthread_join () from /lib/libpthread.so.0
 (gdb) t 2
 [Switching to thread 2 (Thread 0x40800950 (LWP 30972))]#0  thread_execler (arg=0x0)
     at ../../../src/gdb/testsuite/gdb.mi/nsthrexec.c:28
 28        if (execl (image, image, NULL) == -1)
 (gdb) n&
 (gdb) Executing new program: /home/pedro/gdb/sspaces/build-all/gdb/testsuite/gdb.mi/mi-nsthrexec
 
 [LWP 30969] #1 stopped.
 0x00007ffff7dee990 in _dl_debug_state () from /lib64/ld-linux-x86-64.so.2

Not a pretty place to stop.

-- 
Pedro Alves

---
 gdb/infrun.c                          |    8 ++
 gdb/linux-nat.c                       |    5 +
 gdb/testsuite/gdb.mi/mi-nsthrexec.exp |   96 ++++++++++++++++++++++++++++++++++
 gdb/testsuite/gdb.mi/nsthrexec.c      |   48 +++++++++++++++++
 4 files changed, 157 insertions(+)

Index: src/gdb/infrun.c
===================================================================
--- src.orig/gdb/infrun.c	2009-05-27 14:34:33.000000000 +0100
+++ src/gdb/infrun.c	2009-05-27 18:14:22.000000000 +0100
@@ -494,6 +494,14 @@ follow_exec (ptid_t pid, char *execd_pat
   th->step_range_start = 0;
   th->step_range_end = 0;
 
+  /* The target reports the exec event to the main thread, even if
+     some other thread does the exec, and even if the main thread was
+     already stopped --- if debugging in non-stop mode, it's possible
+     the user had the main thread held stopped in the previous image
+     --- release it now.  This is the same behavior as step-over-exec
+     with scheduler-locking on in all-stop mode.  */
+  th->stop_requested = 0;
+
   /* What is this a.out's name? */
   printf_unfiltered (_("Executing new program: %s\n"), execd_pathname);
 
Index: src/gdb/linux-nat.c
===================================================================
--- src.orig/gdb/linux-nat.c	2009-05-27 14:34:33.000000000 +0100
+++ src/gdb/linux-nat.c	2009-05-27 14:35:29.000000000 +0100
@@ -1892,6 +1892,11 @@ linux_handle_extended_wait (struct lwp_i
 
   if (event == PTRACE_EVENT_EXEC)
     {
+      if (debug_linux_nat)
+	fprintf_unfiltered (gdb_stdlog,
+			    "LHEW: Got exec event from LWP %ld\n",
+			    GET_LWP (lp->ptid));
+
       ourstatus->kind = TARGET_WAITKIND_EXECD;
       ourstatus->value.execd_pathname
 	= xstrdup (linux_child_pid_to_exec_file (pid));
Index: src/gdb/testsuite/gdb.mi/mi-nsthrexec.exp
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ src/gdb/testsuite/gdb.mi/mi-nsthrexec.exp	2009-05-27 14:35:29.000000000 +0100
@@ -0,0 +1,96 @@
+# Copyright 2009 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/>.
+
+# No exec event support in the remote protocol.
+if { [is_remote target] } then {
+    continue
+}
+
+load_lib mi-support.exp
+set MIFLAGS "-i=mi"
+
+gdb_exit
+if {[mi_gdb_start]} {
+    continue
+}
+
+#
+# Start here
+#
+set testfile "nsthrexec"
+set srcfile "$testfile.c"
+set binfile "$objdir/$subdir/mi-$testfile"
+
+set options [list debug incdir=$objdir]
+if {[gdb_compile_pthreads "$srcdir/$subdir/$srcfile" $binfile executable $options] != "" } {
+    return -1
+}
+
+mi_gdb_reinitialize_dir $srcdir/$subdir
+mi_gdb_load $binfile
+
+set supported 0
+send_gdb "-gdb-show non-stop\n"
+gdb_expect {
+    -re ".*\\^done,value=\"off\",supported=\"(\[^\"\]+)\"\r\n$mi_gdb_prompt$" {
+	if { $expect_out(1,string) == "1" } {
+	    set supported 1
+	}
+    }
+    -re ".$mi_gdb_prompt$" {
+    }
+}
+
+mi_gdb_test "-gdb-set non-stop 1" ".*"
+mi_gdb_test "-gdb-set target-async 1" ".*"
+detect_async
+
+if { [mi_run_to_main] < 0 } {
+    perror "mi-nsthrexec.exp tests suppressed"
+    continue
+}
+
+mi_create_breakpoint thread_execler 2 keep thread_execler .* .* .* \
+    "breakpoint at thread_execler"
+
+# All threads should stop, except the main thread.
+mi_send_resuming_command "exec-continue --all" "resume all"
+mi_expect_stop "breakpoint-hit" "thread_execler" "\[^\n\]*" "$srcfile" \
+    "\[0-9\]*" {"" "disp=\"keep\""} "stop at thread_execler"
+
+mi_check_thread_states \
+    {"running" "stopped"} \
+    "thread state, execler stopped, main running"
+
+mi_gdb_test "200-exec-interrupt --thread 1" "200\\^done" "interrupt main thread"
+mi_expect_interrupt "main thread interrupted"
+
+mi_check_thread_states {"stopped" "stopped"} "thread state, all stopped"
+
+# now that we know about all the threads, we can get rid of the breakpoints
+mi_delete_breakpoints
+
+mi_create_breakpoint main 3 keep main .* .* .* \
+    "breakpoint at main"
+
+# Now resume the execler thread.  Eventually, it execs.
+mi_send_resuming_command "exec-continue --thread 2" "resume execler thread"
+
+# Check that the main thread passes by the _dl_debug_state internal
+# breakpoint without silently stopping.
+mi_expect_stop "breakpoint-hit" "main" "\[^\n\]*" "$srcfile" \
+    "\[0-9\]*" {"" "disp=\"keep\""} "stop at main after exec"
+
+mi_gdb_exit
Index: src/gdb/testsuite/gdb.mi/nsthrexec.c
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ src/gdb/testsuite/gdb.mi/nsthrexec.c	2009-05-27 14:35:29.000000000 +0100
@@ -0,0 +1,48 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2009 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 <pthread.h>
+#include <unistd.h>
+#include <stdlib.h>
+
+static const char *image;
+
+void *
+thread_execler (void *arg)
+{
+  /* Exec ourselves again.  */
+  if (execl (image, image, NULL) == -1)
+    {
+      perror ("execl");
+      abort ();
+    }
+
+  return NULL;
+}
+
+int
+main (int argc, char **argv)
+{
+  pthread_t thread;
+
+  image = argv[0];
+
+  pthread_create (&thread, NULL, thread_execler, NULL);
+  pthread_join (thread, NULL);
+
+  return 0;
+}