Re: RFC: fix crash when inferior exits during "continue"

Tom Tromey
2012-02-15T20:14:05Z

>>>>> "Pedro" == Pedro Alves <palves@redhat.com> writes:

Pedro> Yeah. We also don't randomly switch to another thread if the previous
Pedro> selected thread exits (and this is the reason we have "exited" threads).
Pedro> Otherwise, if the user is typing

Pedro> (gdb) some_command_that_applies_to_the_current_thread <enter>

Pedro> and the current thread disappears while the user is typing,
Pedro> the command ends up being applied to a random thread, which is
Pedro> not good.

This makes sense to me if the user entered a background command.
But why not switch if the last command was a foreground command?

Pedro> - Make make_cleanup_restore_current_thread "lock" the current
Pedro> inferior, so it isn't removed even if it is "removable".
Pedro> We do something similar for threads -- That's the whole reason
Pedro> for thread_info->refcount. (This is also Jan's suggestion.)

What do you think of the appended?

Tom

2012-02-15 Tom Tromey <tromey@redhat.com>

PR c++/13653:
* thread.c (struct current_thread_cleanup) <was_removable>: New
field.
(do_restore_current_thread_cleanup): Restore 'removable' field.
(restore_current_thread_cleanup_dtor): Likewise.
(make_cleanup_restore_current_thread): Initialize new field.

2012-02-15 Tom Tromey <tromey@redhat.com>

* gdb.base/inferior-died.c: New file.
* gdb.base/inferior-died.exp: New file.

diff --git a/gdb/testsuite/gdb.base/inferior-died.c b/gdb/testsuite/gdb.base/inferior-died.c
new file mode 100644
index 0000000..66227cf
--- /dev/null
+++ b/gdb/testsuite/gdb.base/inferior-died.c
@@ -0,0 +1,37 @@
+/* Test for fork-related gdb bug
+
+ Copyright 2012 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 <stdlib.h>
+#include <stdio.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+void function(void)
+{
+ exit (0); /* Break here */
+}
+
+int main()
+{
+ pid_t child = fork ();
+
+ if (child == 0)
+ function ();
+ else
+ waitpid (child, NULL, 0);
+}
diff --git a/gdb/testsuite/gdb.base/inferior-died.exp b/gdb/testsuite/gdb.base/inferior-died.exp
new file mode 100644
index 0000000..458dd61
--- /dev/null
+++ b/gdb/testsuite/gdb.base/inferior-died.exp
@@ -0,0 +1,56 @@
+# Copyright 2012 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/>.
+
+if { [is_remote target] || ![isnative] } then {
+ unsupported "inferior-died.exp"
+ continue
+}
+
+# Until "set follow-fork-mode" and "catch fork" are implemented on
+# other targets...
+#
+if {![istarget "hppa*-hp-hpux*"] && ![istarget "*-*-linux*"]} then {
+ unsupported "inferior-died.exp"
+ continue
+}
+
+if { ![support_displaced_stepping] } {
+ unsupported "inferior-died.exp"
+ return -1
+}
+
+set testfile "inferior-died"
+set srcfile ${testfile}.c
+set binfile ${objdir}/${subdir}/${testfile}
+
+if { [prepare_for_testing ${testfile}.exp ${testfile} ${testfile}.c] } {
+ return -1
+}
+
+gdb_test_no_output "set detach-on-fork off"
+gdb_test_no_output "set target-async on"
+gdb_test_no_output "set non-stop on"
+
+if ![runto_main] {
+ return
+}
+
+set line [gdb_get_line_number "Break here"]
+gdb_breakpoint $srcfile:$line
+
+gdb_continue_to_breakpoint "breakpoint"
+
+gdb_test "inferior 2" "Switching to inferior 2.*"
+gdb_test "continue" "exited normally.*"
diff --git a/gdb/thread.c b/gdb/thread.c
index 9a29383..c7c9699 100644
--- a/gdb/thread.c
+++ b/gdb/thread.c
@@ -1072,6 +1072,7 @@ struct current_thread_cleanup
int selected_frame_level;
int was_stopped;
int inf_id;
+ int was_removable;
};

static void
@@ -1095,6 +1096,8 @@ do_restore_current_thread_cleanup (void *arg)
set_current_inferior (find_inferior_id (old->inf_id));
}

+ current_inferior ()->removable = old->was_removable;
+
/* The running state of the originally selected thread may have
changed, so we have to recheck it here. */
if (!ptid_equal (inferior_ptid, null_ptid)
@@ -1112,10 +1115,14 @@ restore_current_thread_cleanup_dtor (void *arg)
{
struct current_thread_cleanup *old = arg;
struct thread_info *tp;
+ struct inferior *inf;

tp = find_thread_ptid (old->inferior_ptid);
if (tp)
tp->refcount--;
+ inf = find_inferior_id (old->inf_id);
+ if (inf != NULL)
+ inf->removable = old->was_removable;
xfree (old);
}

@@ -1129,6 +1136,7 @@ make_cleanup_restore_current_thread (void)
old = xmalloc (sizeof (struct current_thread_cleanup));
old->inferior_ptid = inferior_ptid;
old->inf_id = current_inferior ()->num;
+ old->was_removable = current_inferior ()->removable;

if (!ptid_equal (inferior_ptid, null_ptid))
{
@@ -1156,6 +1164,8 @@ make_cleanup_restore_current_thread (void)
tp->refcount++;
}

+ current_inferior ()->removable = 0;
+
return make_cleanup_dtor (do_restore_current_thread_cleanup, old,
restore_current_thread_cleanup_dtor);
}