Here's an example, with the new test:
gdbserver :9999 gdb.threads/kill
gdb gdb.threads/kill
(gdb) b 52
Breakpoint 1 at 0x4007f4: file kill.c, line 52.
Continuing.
Breakpoint 1, main () at kill.c:52
52 return 0; /* set break here */
(gdb) k
Kill the program being debugged? (y or n) y
gdbserver :9999 gdb.threads/kill
Process gdb.base/watch_thread_num created; pid = 9719
Listening on port 1234
Remote debugging from host 127.0.0.1
Killing all inferiors
Segmentation fault (core dumped)
Backtrace:
(gdb) bt
#0 0x00000000004068a0 in find_inferior (list=0x66b060 <all_threads>, func=0x427637 <kill_one_lwp_callback>, arg=0x7fffffffd3fc) at src/gdb/gdbserver/inferiors.c:199
#1 0x00000000004277b6 in linux_kill (pid=15708) at src/gdb/gdbserver/linux-low.c:966
#2 0x000000000041354d in kill_inferior (pid=15708) at src/gdb/gdbserver/target.c:163
#3 0x00000000004107e9 in kill_inferior_callback (entry=0x6704f0) at src/gdb/gdbserver/server.c:2934
#4 0x0000000000406522 in for_each_inferior (list=0x66b050 <all_processes>, action=0x4107a6 <kill_inferior_callback>) at src/gdb/gdbserver/inferiors.c:57
#5 0x0000000000412377 in process_serial_event () at src/gdb/gdbserver/server.c:3767
#6 0x000000000041267c in handle_serial_event (err=0, client_data=0x0) at src/gdb/gdbserver/server.c:3880
#7 0x00000000004189ff in handle_file_event (event_file_desc=4) at src/gdb/gdbserver/event-loop.c:434
#8 0x00000000004181c6 in process_event () at src/gdb/gdbserver/event-loop.c:189
#9 0x0000000000418f45 in start_event_loop () at src/gdb/gdbserver/event-loop.c:552
#10 0x0000000000411272 in main (argc=3, argv=0x7fffffffd8d8) at src/gdb/gdbserver/server.c:3283
The problem is that linux_wait_for_event deletes lwps that have exited
(even those not passed in as lwps of interest), while the lwp/thread
list is being walked on with find_inferior. find_inferior can handle
the current iterated inferior being deleted, but not others.
When killing lwps, we don't really care about any of the pending
status handling of linux_wait_for_event. We can just waitpid the lwps
directly, which is also what GDB does (see
linux-nat.c:kill_wait_callback). This way the lwps are not deleted
while we're walking the list. They'll be deleted by linux_mourn
afterwards.
This crash triggers several times when running the testsuite against
GDBserver with the native-gdbserver board (target remote), but as GDB
can't distinguish between GDBserver crashing and "kill" being
sucessful, as in both cases the connection is closed (the 'k' packet
doesn't require a reply), and the inferior is gone, that results in no
FAIL.
The patch adds a generic test that catches the issue with
extended-remote mode (and works fine with native testing too). Here's
how it fails with the native-extended-gdbserver board without the fix:
(gdb) info threads
Id Target Id Frame
6 Thread 15367.15374 0x000000373bcbc98d in nanosleep () at ../sysdeps/unix/syscall-template.S:81
5 Thread 15367.15373 0x000000373bcbc98d in nanosleep () at ../sysdeps/unix/syscall-template.S:81
4 Thread 15367.15372 0x000000373bcbc98d in nanosleep () at ../sysdeps/unix/syscall-template.S:81
3 Thread 15367.15371 0x000000373bcbc98d in nanosleep () at ../sysdeps/unix/syscall-template.S:81
2 Thread 15367.15370 0x000000373bcbc98d in nanosleep () at ../sysdeps/unix/syscall-template.S:81
* 1 Thread 15367.15367 main () at .../gdb.threads/kill.c:52
(gdb) kill
Kill the program being debugged? (y or n) y
Remote connection closed
^^^^^^^^^^^^^^^^^^^^^^^^
(gdb) FAIL: gdb.threads/kill.exp: kill
Extended remote should remain connected after the kill.
gdb/gdbserver/
2014-07-11 Pedro Alves <palves@redhat.com>
* linux-low.c (kill_wait_lwp): New function, based on
kill_one_lwp_callback, but use my_waitpid directly.
(kill_one_lwp_callback, linux_kill): Use it.
gdb/testsuite/
2014-07-11 Pedro Alves <palves@redhat.com>
* gdb.threads/kill.c: New file.
* gdb.threads/kill.exp: New file.
e76126e8d1