[gdb] Fix hang after ext sigkill
authorTom de Vries <tdevries@suse.de>
Tue, 21 Apr 2020 13:45:57 +0000 (15:45 +0200)
committerTom de Vries <tdevries@suse.de>
Tue, 21 Apr 2020 13:45:57 +0000 (15:45 +0200)
commit4778a5f87d253399083565b4919816f541ebe414
tree0a3bc9701483fbff705eda598775dcc5c5f2ce51
parent946422b6a113063b9bbd72832ed13d4694134597
[gdb] Fix hang after ext sigkill

Consider the test-case from this patch, compiled with pthread support:
...
$ gcc gdb/testsuite/gdb.threads/killed-outside.c -lpthread -g
...

After running to all_started, we can print pid:
...
$ gdb a.out -ex "b all_started" -ex run -ex "delete 1" -ex "p pid"
...
Reading symbols from a.out...
Breakpoint 1 at 0x40072b: file killed-outside.c, line 29.
Starting program: /data/gdb_versions/devel/a.out
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
[New Thread 0x7ffff77fc700 (LWP 3155)]

Thread 1 "a.out" hit Breakpoint 1, all_started () at killed-outside.c:29
29      }
$1 = 3151
(gdb)
...

If we then kill the inferior using an external SIGKILL:
...
(gdb) shell kill -9 3151
...
and subsequently continue:
...
(gdb) c
Continuing.
Couldn't get registers: No such process.
Couldn't get registers: No such process.
(gdb) Couldn't get registers: No such process.
(gdb) Couldn't get registers: No such process.
(gdb) Couldn't get registers: No such process.
<repeat>
...
gdb hangs repeating the same warning.  Typing control-C no longer helps,
and we have to kill gdb.

This is a regression since commit 873657b9e8 "Preserve selected thread in
all-stop w/ background execution".  The commit adds a
scoped_restore_current_thread typed variable restore_thread to
fetch_inferior_event, and the hang is caused by the constructor throwing an
exception.

Fix this by catching the exception in the constructor.

Build and reg-tested on x86_64-linux.

gdb/ChangeLog:

2020-04-21  Tom de Vries  <tdevries@suse.de>

PR gdb/25471
* thread.c
(scoped_restore_current_thread::scoped_restore_current_thread): Catch
exception in get_frame_id.

gdb/testsuite/ChangeLog:

2020-04-21  Tom de Vries  <tdevries@suse.de>

PR gdb/25471
* gdb.threads/killed-outside.c: New test.
* gdb.threads/killed-outside.exp: New file.
gdb/ChangeLog
gdb/testsuite/ChangeLog
gdb/testsuite/gdb.threads/killed-outside.c [new file with mode: 0644]
gdb/testsuite/gdb.threads/killed-outside.exp [new file with mode: 0644]
gdb/thread.c