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When parsing the ptid out of a reply package, if the multi-process
extensions are not supported, use current_inferior's pid as the pid of
the reported thread, instead of inferior_ptid. This is needed because
the inferior_ptid may be null_ptid although a legit context exists,
due to a prior context switch via switch_to_inferior_no_thread.
Below is a scenario that illustrates what could go wrong. First,
setup a multi-target scenario. This is needed, because in a
multi-target setting, the inferior_ptid is cleared out before waiting
on targets. The second inferior below sits on top of a remote target.
Multi-process packets are disabled.
$ # First, spawn a process with PID 26253 to attach to later.
$ gdb-up a.out
Reading symbols from a.out...
(gdb) maint set target-non-stop on
(gdb) set remote multiprocess-feature-packet off
(gdb) start
...
(gdb) add-inferior -no-connection
[New inferior 2]
Added inferior 2
(gdb) inferior 2
[Switching to inferior 2 [<null>] (<noexec>)]
(gdb) target extended-remote | gdbserver --multi -
Remote debugging using | gdbserver --multi -
Remote debugging using stdio
(gdb) attach 26253
Attaching to Remote target
Attached; pid = 26253
[New Thread 26253]
[New inferior 3]
Reading /tmp/a.out from remote target...
...
[New Thread 26253]
...
Reading /usr/local/lib/debug/....debug from remote target...
>>> GDB seems to hang here.
After attaching to a process and reading some library files, GDB
seems to hang. One interesting thing to note is that
[New Thread 26253]
appears twice. We also see
[New inferior 3]
Running the same scenario with "debug infrun on" reveals more details.
...
(gdb) attach 26253
[infrun] scoped_disable_commit_resumed: reason=attaching
Attaching to Remote target
Attached; pid = 26253
[New Thread 26253]
[infrun] infrun_async: enable=1
[infrun] attach_command: immediately after attach:
[infrun] attach_command: thread 26253.26253.0, executing = 1, resumed = 0, state = RUNNING
[infrun] clear_proceed_status_thread: 26253.26253.0
[infrun] reset: reason=attaching
[infrun] maybe_set_commit_resumed_all_targets: not requesting commit-resumed for target native, no resumed threads
[infrun] maybe_set_commit_resumed_all_targets: enabling commit-resumed for target extended-remote
[infrun] fetch_inferior_event: enter
[infrun] scoped_disable_commit_resumed: reason=handling event
[infrun] do_target_wait: Found 2 inferiors, starting at #1
[infrun] random_pending_event_thread: None found.
[infrun] print_target_wait_results: target_wait (-1.0.0 [Thread 0], status) =
[infrun] print_target_wait_results: 26253.26253.0 [Thread 26253],
[infrun] print_target_wait_results: status->kind = STOPPED, sig = GDB_SIGNAL_0
[infrun] handle_inferior_event: status->kind = STOPPED, sig = GDB_SIGNAL_0
[infrun] start_step_over: enter
[infrun] start_step_over: stealing global queue of threads to step, length = 0
[infrun] operator(): step-over queue now empty
[infrun] start_step_over: exit
[infrun] context_switch: Switching context from 0.0.0 to 26253.26253.0
[infrun] handle_signal_stop: stop_pc=0x7f849d8cf151
[infrun] stop_waiting: stop_waiting
[infrun] stop_all_threads: starting
[infrun] stop_all_threads: pass=0, iterations=0
[New inferior 3]
Reading /tmp/a.out from remote target...
warning: File transfers from remote targets can be slow. Use "set sysroot" to access files locally instead.
Reading /tmp/a.out from remote target...
Reading symbols from target:/tmp/a.out...
[New Thread 26253]
[infrun] stop_all_threads: 4723.4723.0 not executing
[infrun] stop_all_threads: 26253.26253.0 not executing
[infrun] stop_all_threads: 42000.26253.0 executing, need stop
[infrun] print_target_wait_results: target_wait (-1.0.0 [Thread 0], status) =
[infrun] print_target_wait_results: -1.0.0 [Thread 0],
[infrun] print_target_wait_results: status->kind = IGNORE
[infrun] print_target_wait_results: target_wait (-1.0.0 [Thread 0], status) =
[infrun] print_target_wait_results: -1.0.0 [Thread 0],
[infrun] print_target_wait_results: status->kind = IGNORE
GDB tried to stop Thread 42000.26253.0, which does not exist, and we
are waiting for a stop event that will never happen. The PID in
'42000.26253.0', namely 42000, is the PID of magic_null_ptid.
It comes from gdb/remote.c:read_ptid:
/* Since the stub is not sending a process id, then default to
what's in inferior_ptid, unless it's null at this point. If so,
then since there's no way to know the pid of the reported
threads, use the magic number. */
if (inferior_ptid == null_ptid)
pid = magic_null_ptid.pid ();
else
pid = inferior_ptid.pid ();
if (obuf)
*obuf = pp;
return ptid_t (pid, tid);
Because multi-process was turned off, GDB did not parse an explicitly
specified PID. Furthermore, inferior_ptid == null_ptid, and
eventually GDB picked the PID from magic_null_ptid.
If target-non-stop is not turned on at the beginning, the same bug
reveals itself as a duplicated thread as shown below.
# Same setup as above, without 'maint set target-non-stop on'.
...
(gdb) attach 26253
Attaching to Remote target
Attached; pid = 26253
[New inferior 3]
...
[New Thread 26253]
...
(gdb) info threads
Id Target Id Frame
1.1 process 13517 "a.out" main () at test.c:3
* 2.1 Thread 26253 "a.out" 0x00007f12750c5151 in read () from target:/lib/x86_64-linux-gnu/libc.so.6
3.1 Thread 26253 "a.out" Remote 'g' packet reply is too long (expected 560 bytes, got 2496 bytes): 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
(gdb)
Fix the problem by preferring current_inferior()'s pid instead of
magic_null_ptid.
Regression-tested on X86-64 Linux.
Co-authored-by: Aleksandar Paunovic <aleksandar.paunovic@intel.com>
35 lines
1.0 KiB
C
35 lines
1.0 KiB
C
/* This testcase is part of GDB, the GNU debugger.
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Copyright 2020-2022 Free Software Foundation, Inc.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>. */
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/* This program is intended to be started outside of GDB, and then
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attached to by GDB. */
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#include <unistd.h>
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int
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main ()
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{
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/* Don't run forever in case GDB crashes and DejaGNU fails to kill
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this program. */
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alarm (10);
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while (1)
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usleep (1);
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return 0;
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}
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