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Re: [RFC][PATCH] GDB kills itself instead of interrupting inferior
- From: Pedro Alves <palves at redhat dot com>
- To: Cyril Nikolaev <cyril at nichtverstehen dot de>
- Cc: gdb-patches at sourceware dot org
- Date: Fri, 26 Jul 2013 12:35:47 +0100
- Subject: Re: [RFC][PATCH] GDB kills itself instead of interrupting inferior
- References: <CAMx6oW7asrxWqsZZB1Ej6FAwmmP0y8KOHm8zYeV6ACe-cK_rsw at mail dot gmail dot com>
Hi!
Very sorry for the slow response on this.
On 02/15/2013 05:34 PM, Cyril Nikolaev wrote:
> Hi! When GDB is run with IO redirected to a pipe, 'interrupt' command
> causes it to kill its own process group instead of the inferior. The
> problem manifests itself in async mode:
>
> $ cat | gdb <file>
> (gdb) set target-async on
> (gdb) run &
> (gdb) interrupt
> A debugging session is active.
> Inferior 1 [process 20584] will be killed.
> Quit anyway? (y or n) [answered Y; input not from terminal]
>
> In this case GDB tells that its stdin isn't a tty and doesn't save
> inferior process group in `inflow.c:terminal_init_inferior_with_pgrp`
> which is wrong. And then when it receives `interrupt` command
> it `kill`'s process group 0 in `inf-ptrace.c:inf_ptrace_stop` instead
> of inferior process group.
>
> When GDB is used from SublimeGDB (debugging plugin for Sublime Text
> editor) that means killing its own process group including Sublime
> and possibly X session. There is a corresponding issue in SublimeGDB
> bug tracker: https://github.com/quarnster/SublimeGDB/issues/29.
>
> I suppose GDB should save inferior pgid regardless of having its
> terminal as pgid is valuable not only to reset foreground process
> group, but also to interrupt inferior.
>
> I attach a patch that is supposed to do that. I am very new to GDB
> code. Does it look ok?
Yep, thanks! It just needed a regression test. I went ahead and wrote
one. I mulled over how to spawn GDB like in your reproducer (eventually
had a wrapper shell script, and pointed the tcl GDB variable to it),
but then realized that "set interactive-mode off" is enough to trigger
badness:
...
(gdb) interrupt
(gdb) Quit
(gdb) interrupt
(gdb) Quit
...
GDB doesn't quit, but that's immaterial.
Testing with GDBserver exposed a race, where "interrupt" right after
"continue&" would occasionally do nothing, leading to spurious fails.
This is related to target remote ctrl-c issues being addressed on
another thread, where ctrl-c is swallowed in some conditions. I've
worked around them in the test (and added a comment).
I took the liberty of adjusting/expanding your email's text, and
using it as commit log. Below's what I checked in.
(I noticed that in the current code, the inferior's process group
is _always_ the inferior's PID, so that could be simplified.
The "This is for Lynx" comment in terminal_init_inferior is no
longer relevant, given we don't support native Lynx debugging
anymore.)
--------
GDB kills itself instead of interrupting inferior
When GDB is run with IO redirected to a pipe, the 'interrupt' command
causes it to kill its own process group instead of the inferior's.
The problem manifests itself in async mode, native debugging:
$ cat | gdb <file>
(gdb) set target-async on
(gdb) run &
(gdb) interrupt
A debugging session is active.
Inferior 1 [process 20584] will be killed.
Quit anyway? (y or n) [answered Y; input not from terminal]
In this case, GDB tells that its stdin isn't a tty and doesn't save
the inferior's process group in
inflow.c:terminal_init_inferior_with_pgrp. The 'interrupt' command
tries to 'kill' the inferior's process group in
`inf-ptrace.c:inf_ptrace_stop`, but since that wasn't saved in the
first place, GDB kills process group 0, meaning, its own process
group.
When GDB is used from a frontend, that means killing its own process
group including the frontend and possibly the X session. This was
originally seen with SublimeGDB:
https://github.com/quarnster/SublimeGDB/issues/29.
The patch makes GDB save the inferior pgid regardless of having a
terminal, as pgid is used not only to reset foreground process group,
but also to interrupt the inferior process. It also adds a regression
test. Luckily, we can emulate not having a terminal with "set
interactive-mode off", avoiding the need of special magic to spawn gdb
with a pipe.
Tested on x86_64 Fedora 17.
gdb/
2013-07-26 Cyril Nikolaev <cyril@nichtverstehen.de>
* inflow.c (terminal_init_inferior_with_pgrp): Save inferior
process group regardless of having tty on stdin.
gdb/testsuite/
2013-07-26 Pedro Alves <palves@redhat.com>
* gdb.base/interrupt-noterm.c, gdb.base/interrupt-noterm.exp: New
files.
---
gdb/inflow.c | 17 ++++---
gdb/testsuite/gdb.base/interrupt-noterm.c | 25 ++++++++++
gdb/testsuite/gdb.base/interrupt-noterm.exp | 76 +++++++++++++++++++++++++++++
3 files changed, 111 insertions(+), 7 deletions(-)
create mode 100644 gdb/testsuite/gdb.base/interrupt-noterm.c
create mode 100644 gdb/testsuite/gdb.base/interrupt-noterm.exp
diff --git a/gdb/inflow.c b/gdb/inflow.c
index 79a99d1..faf4888 100644
--- a/gdb/inflow.c
+++ b/gdb/inflow.c
@@ -217,19 +217,22 @@ static void terminal_ours_1 (int);
void
terminal_init_inferior_with_pgrp (int pgrp)
{
+ struct inferior *inf = current_inferior ();
+ struct terminal_info *tinfo = get_inflow_inferior_data (inf);
+
+#ifdef PROCESS_GROUP_TYPE
+ /* Store the process group even without a terminal as it is used not
+ only to reset the tty foreground process group, but also to
+ interrupt the inferior. */
+ tinfo->process_group = pgrp;
+#endif
+
if (gdb_has_a_terminal ())
{
- struct inferior *inf = current_inferior ();
- struct terminal_info *tinfo = get_inflow_inferior_data (inf);
-
xfree (tinfo->ttystate);
tinfo->ttystate = serial_copy_tty_state (stdin_serial,
our_terminal_info.ttystate);
-#ifdef PROCESS_GROUP_TYPE
- tinfo->process_group = pgrp;
-#endif
-
/* Make sure that next time we call terminal_inferior (which will be
before the program runs, as it needs to be), we install the new
process group. */
diff --git a/gdb/testsuite/gdb.base/interrupt-noterm.c b/gdb/testsuite/gdb.base/interrupt-noterm.c
new file mode 100644
index 0000000..264b0b0
--- /dev/null
+++ b/gdb/testsuite/gdb.base/interrupt-noterm.c
@@ -0,0 +1,25 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+ Copyright (C) 2013 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 <unistd.h>
+
+int
+main ()
+{
+ sleep (3);
+ return 0;
+}
diff --git a/gdb/testsuite/gdb.base/interrupt-noterm.exp b/gdb/testsuite/gdb.base/interrupt-noterm.exp
new file mode 100644
index 0000000..42d17b1
--- /dev/null
+++ b/gdb/testsuite/gdb.base/interrupt-noterm.exp
@@ -0,0 +1,76 @@
+# Copyright (C) 2013 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/>.
+
+standard_testfile
+
+if [prepare_for_testing "failed to prepare for testing" \
+ ${testfile} ${srcfile} {debug}] {
+ return -1
+}
+
+# Pretend there's no terminal.
+gdb_test_no_output "set interactive-mode off"
+gdb_test_no_output "set target-async on"
+
+if ![runto main] {
+ fail "Can't run to main"
+ return -1
+}
+
+# Delete breakpoints so that the next resume is a plain continue,
+# instead of a step-over-breakpoint sequence just while GDB sends the
+# interrupt request. If that's buggy on some targets (and it was on
+# target remote for a while, where a ctrl-c at the wrong time will get
+# lost), then it should get its own specific test. Disable
+# confirmation, avoiding complications caused by the fact that we've
+# disabled the terminal -- GDB would auto-answer "yes", confusing
+# gdb_test_multiple.
+gdb_test_no_output "set confirm off"
+gdb_test_no_output "delete"
+gdb_test_no_output "set confirm on"
+
+set async_supported -1
+set test "continue &"
+gdb_test_multiple $test $test {
+ -re "Continuing\\.\r\n$gdb_prompt $" {
+ set async_supported 1
+ pass $test
+ }
+ -re ".*Asynchronous execution not supported on this target..*" {
+ unsupported $test
+ }
+}
+if { $async_supported < 0 } {
+ return 1
+}
+
+# With native debugging, and no terminal (emulated by interactive-mode
+# off, above), GDB had a bug where "interrupt" would send SIGINT to
+# its own process group, instead of the inferior's.
+set test "interrupt"
+gdb_test_multiple $test $test {
+ -re "interrupt\r\n$gdb_prompt " {
+ pass $test
+ }
+}
+
+set test "inferior received SIGINT"
+gdb_test_multiple "" $test {
+ -re "\r\nProgram received signal SIGINT.*" {
+ # This appears after the prompt, which was already consumed
+ # above.
+ pass $test
+ }
+}
--
1.7.11.7