Re: [PATCH 03/31] gdb/linux: Delete all other LWPs immediately on ptrace exec event

Pedro Alves
2023-04-14T19:29:30Z

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Hi!

On 2023-04-04 2:57 p.m., Pedro Alves wrote:
> On 2023-03-21 2:50 p.m., Andrew Burgess wrote:
>>
>> I thought it was the second case, but I was so unsure that I tried the
>> reproducer anyway. Just in case I'm wrong, the above example doesn't
>> seem to fail prior to this commit.
>
> This surprised me, and when I tried it myself, I was even more surprised,
> for I couldn't reproduce it either!
>
> But I figured it out.
>
> I'm usually using Ubuntu 22.04 for development nowadays, and in that system, indeed I can't
> reproduce it. Right after the exec, GDB traps a load event for "libc.so.6", which leads to
> gdb trying to open libthread_db for the post-exec inferior, and, it succeeds. When we load
> libthread_db, we call linux_stop_and_wait_all_lwps, which, as the name suggests, stops all lwps,
> and then waits to see their stops. While doing this, GDB detects that the pre-exec stale
> LWP is gone, and deletes it.
>
> The logs show:
>
> [linux-nat] linux_nat_wait_1: waitpid 1725529 received SIGTRAP - Trace/breakpoint trap (stopped)
> [linux-nat] save_stop_reason: 1725529.1725529.0 stopped by software breakpoint
> [linux-nat] linux_nat_wait_1: waitpid(-1, ...) returned 0, ERRNO-OK
> [linux-nat] resume_stopped_resumed_lwps: NOT resuming LWP 1725529.1725658.0, not stopped
> [linux-nat] resume_stopped_resumed_lwps: NOT resuming LWP 1725529.1725529.0, has pending status
> [linux-nat] linux_nat_wait_1: trap ptid is 1725529.1725529.0.
> [linux-nat] linux_nat_wait_1: exit
> [linux-nat] stop_callback: kill 1725529.1725658.0 **<SIGSTOP>**
> [linux-nat] stop_callback: lwp kill -1 No such process
> [linux-nat] wait_lwp: 1725529.1725658.0 vanished.
>
> And the backtrace is:
>
> (top-gdb) bt
> #0 wait_lwp (lp=0x555556f37350) at ../../src/gdb/linux-nat.c:2069
> #1 0x0000555555aa8fbf in stop_wait_callback (lp=0x555556f37350) at ../../src/gdb/linux-nat.c:2375
> #2 0x0000555555ab12b3 in gdb::function_view<int (lwp_info*)>::bind<int, lwp_info*>(int (*)(lwp_info*))::{lambda(gdb::fv_detail::erased_callable, lwp_info*)#1}::operator()(gdb::fv_detail::erased_callable, lwp_info*) const (__closure=0x0, ecall=..., args#0=0x555556f37350) at ../../src/gdb/../gdbsupport/function-view.h:326
> #3 0x0000555555ab12e2 in gdb::function_view<int (lwp_info*)>::bind<int, lwp_info*>(int (*)(lwp_info*))::{lambda(gdb::fv_detail::erased_callable, lwp_info*)#1}::_FUN(gdb::fv_detail::erased_callable, lwp_info*) () at ../../src/gdb/../gdbsupport/function-view.h:320
> #4 0x0000555555ab0610 in gdb::function_view<int (lwp_info*)>::operator()(lwp_info*) const (this=0x7fffffffca90, args#0=0x555556f37350) at ../../src/gdb/../gdbsupport/function-view.h:289
> #5 0x0000555555aa4c2d in iterate_over_lwps(ptid_t, gdb::function_view<int (lwp_info*)>) (filter=..., callback=...) at ../../src/gdb/linux-nat.c:867
> #6 0x0000555555aa8a03 in linux_stop_and_wait_all_lwps () at ../../src/gdb/linux-nat.c:2229
> #7 0x0000555555ac8525 in try_thread_db_load_1 (info=0x555556a66dd0) at ../../src/gdb/linux-thread-db.c:923
> #8 0x0000555555ac89d5 in try_thread_db_load (library=0x5555560eca27 "libthread_db.so.1", check_auto_load_safe=false) at ../../src/gdb/linux-thread-db.c:1024
> #9 0x0000555555ac8eda in try_thread_db_load_from_sdir () at ../../src/gdb/linux-thread-db.c:1108
> #10 0x0000555555ac9278 in thread_db_load_search () at ../../src/gdb/linux-thread-db.c:1163
> #11 0x0000555555ac9518 in thread_db_load () at ../../src/gdb/linux-thread-db.c:1225
> #12 0x0000555555ac95e1 in check_for_thread_db () at ../../src/gdb/linux-thread-db.c:1268
> #13 0x0000555555ac9657 in thread_db_new_objfile (objfile=0x555556943ed0) at ../../src/gdb/linux-thread-db.c:1297
> #14 0x000055555569e2d2 in std::__invoke_impl<void, void (*&)(objfile*), objfile*> (__f=@0x5555567925d8: 0x555555ac95e8 <thread_db_new_objfile(objfile*)>) at /usr/include/c++/11/bits/invoke.h:61
> #15 0x000055555569c44a in std::__invoke_r<void, void (*&)(objfile*), objfile*> (__fn=@0x5555567925d8: 0x555555ac95e8 <thread_db_new_objfile(objfile*)>) at /usr/include/c++/11/bits/invoke.h:111
> #16 0x0000555555699d69 in std::_Function_handler<void (objfile*), void (*)(objfile*)>::_M_invoke(std::_Any_data const&, objfile*&&) (__functor=..., __args#0=@0x7fffffffce50: 0x555556943ed0) at /usr/include/c++/11/bits/std_function.h:290
> #17 0x0000555555b5f48b in std::function<void (objfile*)>::operator()(objfile*) const (this=0x5555567925d8, __args#0=0x555556943ed0) at /usr/include/c++/11/bits/std_function.h:590
> #18 0x0000555555b5eba4 in gdb::observers::observable<objfile*>::notify (this=0x5555565b5680 <gdb::observers::new_objfile>, args#0=0x555556943ed0) at ../../src/gdb/../gdbsupport/observable.h:166
> #19 0x0000555555cdd85b in symbol_file_add_with_addrs (abfd=..., name=0x5555569794e0 "/lib/x86_64-linux-gnu/libc.so.6", add_flags=..., addrs=0x7fffffffd0c0, flags=..., parent=0x0) at ../../src/gdb/symfile.c:1131
> #20 0x0000555555cdd9c5 in symbol_file_add_from_bfd (abfd=..., name=0x5555569794e0 "/lib/x86_64-linux-gnu/libc.so.6", add_flags=..., addrs=0x7fffffffd0c0, flags=..., parent=0x0) at ../../src/gdb/symfile.c:1167
> #21 0x0000555555c9dd69 in solib_read_symbols (so=0x5555569792d0, flags=...) at ../../src/gdb/solib.c:730
> #22 0x0000555555c9e7b7 in solib_add (pattern=0x0, from_tty=0, readsyms=1) at ../../src/gdb/solib.c:1041
> #23 0x0000555555c9f61d in handle_solib_event () at ../../src/gdb/solib.c:1315
> #24 0x0000555555729c26 in bpstat_stop_status (aspace=0x555556606800, bp_addr=0x7ffff7fe7278, thread=0x555556816bd0, ws=..., stop_chain=0x0) at ../../src/gdb/breakpoint.c:5702
> #25 0x0000555555a62e41 in handle_signal_stop (ecs=0x7fffffffd670) at ../../src/gdb/infrun.c:6517
> #26 0x0000555555a61479 in handle_inferior_event (ecs=0x7fffffffd670) at ../../src/gdb/infrun.c:6000
> #27 0x0000555555a5c7b5 in fetch_inferior_event () at ../../src/gdb/infrun.c:4403
> #28 0x0000555555a35b65 in inferior_event_handler (event_type=INF_REG_EVENT) at ../../src/gdb/inf-loop.c:41
> #29 0x0000555555aae0c9 in handle_target_event (error=0, client_data=0x0) at ../../src/gdb/linux-nat.c:4231
>
>
> Now, when I try the same on a Fedora 32 machine, I see the GDB crash due to the stale
> LWP still in the LWP list with no corresponding thread_info. On this
> machine, glibc predates the changes that make it possible to use libthread_db with
> non-threaded processes, so try_thread_db_load doesn't manage to open a connection
> to libthread_db, and thus we don't end up in linux_stop_and_wait_all_lwps, and thus
> the stale lwp is not deleted. And so a subsequent "kill" command crashes.
>
> I wrote that patch originally on an Ubuntu 20.04 machine (vs the Ubuntu 22.04 I have now),
> and it must be that that version also predates the glibc change, and thus behaves like
> this Fedora 32 box. You are very likely using a newer Fedora which has the glibc change.

...

>> What are your thoughts on including this, or something like this with
>> this commit? My patch, which applies on top of this commit, is included
>> at the end of this email. Please feel free to take any changes that you
>> feel add value.
>
> I'm totally fine with such a command, though the test I had added covers
> as much as it would, as the "kill" command fails when the maint command
> would fail, and passes when the maint command passes. But I'll incorporate
> it.
>

I realized that my description of the problem above practically
suggests a way to expose the crash everywhere -- just catch the exec
event with "catch exec", so that the post-exec program doesn't even
get to the libc.so.6 load event, and issue "kill" there, or use "maint info linux-lwps".
So I've adjusted the patch to add a new testcase doing that. I've attached two
patches, one adding your "maint info linux-lwps", now with NEWS/docs, and
the updated version of the crash fix and testcase.

WDYT?

Pedro Alves

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From 450e0133fc884f027cce4ae65378ea5560f6464d Mon Sep 17 00:00:00 2001
From: Andrew Burgess <aburgess@redhat.com>
Date: Tue, 4 Apr 2023 14:50:35 +0100
Subject: [PATCH 1/2] Add "maint info linux-lwps" command

This adds a maintenance command that lets you list all the LWPs under
control of the linux-nat target.

For example:

(gdb) maint info linux-lwps
LWP Ptid Thread ID
560948.561047.0 None
560948.560948.0 1.1

This shows that "560948.561047.0" LWP doesn't map to any thread_info
object, which is bogus. We'll be using this in a testcase in a
following patch.

Co-Authored-By: Pedro Alves <pedro@palves.net>
Change-Id: Ic4e9e123385976e5cd054391990124b7a20fb3f5
---
gdb/NEWS | 3 +++
gdb/doc/gdb.texinfo | 4 ++++
gdb/linux-nat.c | 46 +++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 53 insertions(+)

diff --git a/gdb/NEWS b/gdb/NEWS
index d729aa24056..3747e7d52c1 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -78,6 +78,9 @@ maintenance info frame-unwinders
maintenance wait-for-index-cache
Wait until all pending writes to the index cache have completed.

+maintenance info linux-lwps
+ List all LWPs under control of the linux-nat target.
+
set always-read-ctf on|off
show always-read-ctf
When off, CTF is only read if DWARF is not present. When on, CTF is
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 6c811b8be2e..398bbb88af6 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -40605,6 +40605,10 @@ module (@pxref{Disassembly In Python}), and will only be present after
that module has been imported. To force the module to be imported do
the following:

+@kindex maint info linux-lwps
+@item maint info linux-lwps
+Print information about LWPs under control of the Linux native target.
+
@smallexample
(@value{GDBP}) python import gdb.disassembler
@end smallexample
diff --git a/gdb/linux-nat.c b/gdb/linux-nat.c
index 944f23de01a..68816ddc999 100644
--- a/gdb/linux-nat.c
+++ b/gdb/linux-nat.c
@@ -4479,6 +4479,49 @@ current_lwp_ptid (void)
return inferior_ptid;
}

+/* Implement 'maintenance info linux-lwps'. Displays some basic
+ information about all the current lwp_info objects. */
+
+static void
+maintenance_info_lwps (const char *arg, int from_tty)
+{
+ if (all_lwps ().size () == 0)
+ {
+ gdb_printf ("No Linux LWPs\n");
+ return;
+ }
+
+ /* Start the width at 8 to match the column heading below, then
+ figure out the widest ptid string. We'll use this to build our
+ output table below. */
+ size_t ptid_width = 8;
+ for (lwp_info *lp : all_lwps ())
+ ptid_width = std::max (ptid_width, lp->ptid.to_string ().size ());
+
+ /* Setup the table headers. */
+ struct ui_out *uiout = current_uiout;
+ ui_out_emit_table table_emitter (uiout, 2, -1, "linux-lwps");
+ uiout->table_header (ptid_width, ui_left, "lwp-ptid", _("LWP Ptid"));
+ uiout->table_header (9, ui_left, "thread-info", _("Thread ID"));
+ uiout->table_body ();
+
+ /* Display one table row for each lwp_info. */
+ for (lwp_info *lp : all_lwps ())
+ {
+ ui_out_emit_tuple tuple_emitter (uiout, "lwp-entry");
+
+ struct thread_info *th = find_thread_ptid (linux_target, lp->ptid);
+
+ uiout->field_string ("lwp-ptid", lp->ptid.to_string ().c_str ());
+ if (th == nullptr)
+ uiout->field_string ("thread-info", "None");
+ else
+ uiout->field_string ("thread-info", print_full_thread_id (th));
+
+ uiout->message ("\n");
+ }
+}
+
void _initialize_linux_nat ();
void
_initialize_linux_nat ()
@@ -4516,6 +4559,9 @@ Enables printf debugging output."),
sigemptyset (&blocked_mask);

lwp_lwpid_htab_create ();
+
+ add_cmd ("linux-lwps", class_maintenance, maintenance_info_lwps,
+ _("List the Linux LWPS."), &maintenanceinfolist);
}
\f

base-commit: 57573e54afb9f7ed957eec43dfd2830f2384c970
prerequisite-patch-id: 3a896bfe4b7c66a2e3a6aa668c5ae8395e5d8a52
--
2.36.0

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[-- Type: text/x-patch, Size: 11883 bytes --]

From ee0a276c08b829ae504fe0eba5badc4f7faf3676 Mon Sep 17 00:00:00 2001
From: Pedro Alves <pedro@palves.net>
Date: Wed, 13 Jul 2022 17:16:38 +0100
Subject: [PATCH 2/2] gdb/linux: Delete all other LWPs immediately on ptrace
exec event

I noticed that on an Ubuntu 20.04 system, after a following patch
("Step over clone syscall w/ breakpoint,
TARGET_WAITKIND_THREAD_CLONED"), the gdb.threads/step-over-exec.exp
was passing cleanly, but still, we'd end up with four new unexpected
GDB core dumps:

=== gdb Summary ===

# of unexpected core files 4
# of expected passes 48

That said patch is making the pre-existing
gdb.threads/step-over-exec.exp testcase (almost silently) expose a
latent problem in gdb/linux-nat.c, resulting in a GDB crash when:

#1 - a non-leader thread execs
#2 - the post-exec program stops somewhere
#3 - you kill the inferior

Instead of #3 directly, the testcase just returns, which ends up in
gdb_exit, tearing down GDB, which kills the inferior, and is thus
equivalent to #3 above.

Vis:

$ gdb --args ./gdb /home/pedro/gdb/build/gdb/testsuite/outputs/gdb.threads/step-over-exec/step-over-exec-execr-thread-other-diff-text-segs-true
...
(top-gdb) r
...
(gdb) b main
...
(gdb) r
...
Breakpoint 1, main (argc=1, argv=0x7fffffffdb88) at /home/pedro/gdb/build/gdb/testsuite/../../../src/gdb/testsuite/gdb.threads/step-over-exec.c:69
69 argv0 = argv[0];
(gdb) c
Continuing.
[New Thread 0x7ffff7d89700 (LWP 2506975)]
Other going in exec.
Exec-ing /home/pedro/gdb/build/gdb/testsuite/outputs/gdb.threads/step-over-exec/step-over-exec-execr-thread-other-diff-text-segs-true-execd
process 2506769 is executing new program: /home/pedro/gdb/build/gdb/testsuite/outputs/gdb.threads/step-over-exec/step-over-exec-execr-thread-other-diff-text-segs-true-execd

Thread 1 "step-over-exec-" hit Breakpoint 1, main () at /home/pedro/gdb/build/gdb/testsuite/../../../src/gdb/testsuite/gdb.threads/step-over-exec-execd.c:28
28 foo ();
(gdb) k
...
Thread 1 "gdb" received signal SIGSEGV, Segmentation fault.
0x000055555574444c in thread_info::has_pending_waitstatus (this=0x0) at ../../src/gdb/gdbthread.h:393
393 return m_suspend.waitstatus_pending_p;
(top-gdb) bt
#0 0x000055555574444c in thread_info::has_pending_waitstatus (this=0x0) at ../../src/gdb/gdbthread.h:393
#1 0x0000555555a884d1 in get_pending_child_status (lp=0x5555579b8230, ws=0x7fffffffd130) at ../../src/gdb/linux-nat.c:1345
#2 0x0000555555a8e5e6 in kill_unfollowed_child_callback (lp=0x5555579b8230) at ../../src/gdb/linux-nat.c:3564
#3 0x0000555555a92a26 in gdb::function_view<int (lwp_info*)>::bind<int, lwp_info*>(int (*)(lwp_info*))::{lambda(gdb::fv_detail::erased_callable, lwp_info*)#1}::operator()(gdb::fv_detail::erased_callable, lwp_info*) const (this=0x0, ecall=..., args#0=0x5555579b8230) at ../../src/gdb/../gdbsupport/function-view.h:284
#4 0x0000555555a92a51 in gdb::function_view<int (lwp_info*)>::bind<int, lwp_info*>(int (*)(lwp_info*))::{lambda(gdb::fv_detail::erased_callable, lwp_info*)#1}::_FUN(gdb::fv_detail::erased_callable, lwp_info*) () at ../../src/gdb/../gdbsupport/function-view.h:278
#5 0x0000555555a91f84 in gdb::function_view<int (lwp_info*)>::operator()(lwp_info*) const (this=0x7fffffffd210, args#0=0x5555579b8230) at ../../src/gdb/../gdbsupport/function-view.h:247
#6 0x0000555555a87072 in iterate_over_lwps(ptid_t, gdb::function_view<int (lwp_info*)>) (filter=..., callback=...) at ../../src/gdb/linux-nat.c:864
#7 0x0000555555a8e732 in linux_nat_target::kill (this=0x55555653af40 <the_amd64_linux_nat_target>) at ../../src/gdb/linux-nat.c:3590
#8 0x0000555555cfdc11 in target_kill () at ../../src/gdb/target.c:911
...

The root of the problem is that when a non-leader LWP execs, it just
changes its tid to the tgid, replacing the pre-exec leader thread,
becoming the new leader. There's no thread exit event for the execing
thread. It's as if the old pre-exec LWP vanishes without trace. The
ptrace man page says:

"PTRACE_O_TRACEEXEC (since Linux 2.5.46)
Stop the tracee at the next execve(2). A waitpid(2) by the
tracer will return a status value such that

status>>8 == (SIGTRAP | (PTRACE_EVENT_EXEC<<8))

If the execing thread is not a thread group leader, the thread
ID is reset to thread group leader's ID before this stop.
Since Linux 3.0, the former thread ID can be retrieved with
PTRACE_GETEVENTMSG."

When the core of GDB processes an exec events, it deletes all the
threads of the inferior. But, that is too late -- deleting the thread
does not delete the corresponding LWP, so we end leaving the pre-exec
non-leader LWP stale in the LWP list. That's what leads to the crash
above -- linux_nat_target::kill iterates over all LWPs, and after the
patch in question, that code will look for the corresponding
thread_info for each LWP. For the pre-exec non-leader LWP still
listed, won't find one.

This patch fixes it, by deleting the pre-exec non-leader LWP (and
thread) from the LWP/thread lists as soon as we get an exec event out
of ptrace.

GDBserver does not need an equivalent fix, because it is already doing
this, as side effect of mourning the pre-exec process, in
gdbserver/linux-low.cc:

else if (event == PTRACE_EVENT_EXEC && cs.report_exec_events)
{
...
/* Delete the execing process and all its threads. */
mourn (proc);
switch_to_thread (nullptr);

The crash with gdb.threads/step-over-exec.exp is not observable on
newer systems, which postdate the glibc change to move "libpthread.so"
internals to "libc.so.6", because right after the exec, GDB traps a
load event for "libc.so.6", which leads to GDB trying to open
libthread_db for the post-exec inferior, and, on such systems that
succeeds. When we load libthread_db, we call
linux_stop_and_wait_all_lwps, which, as the name suggests, stops all
lwps, and then waits to see their stops. While doing this, GDB
detects that the pre-exec stale LWP is gone, and deletes it.

If we use "catch exec" to stop right at the exec before the
"libc.so.6" load event ever happens, and issue "kill" right there,
then GDB crashes on newer systems as well. So instead of tweaking
gdb.threads/step-over-exec.exp to cover the fix, add a new
gdb.threads/threads-after-exec.exp testcase that uses "catch exec".

Also tweak a comment in infrun.c:follow_exec referring to how
linux-nat.c used to behave, as it would become stale otherwise.

Change-Id: I21ec18072c7750f3a972160ae6b9e46590376643
---
gdb/infrun.c | 8 +--
gdb/linux-nat.c | 15 ++++
.../gdb.threads/threads-after-exec.exp | 70 +++++++++++++++++++
3 files changed, 88 insertions(+), 5 deletions(-)
create mode 100644 gdb/testsuite/gdb.threads/threads-after-exec.exp

diff --git a/gdb/infrun.c b/gdb/infrun.c
index abe49ae0f2f..93edc224622 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -1224,13 +1224,11 @@ follow_exec (ptid_t ptid, const char *exec_file_target)
some other thread does the exec, and even if the main thread was
stopped or already gone. We may still have non-leader threads of
the process on our list. E.g., on targets that don't have thread
- exit events (like remote); or on native Linux in non-stop mode if
- there were only two threads in the inferior and the non-leader
- one is the one that execs (and nothing forces an update of the
- thread list up to here). When debugging remotely, it's best to
+ exit events (like remote) and nothing forces an update of the
+ thread list up to here. When debugging remotely, it's best to
avoid extra traffic, when possible, so avoid syncing the thread
list with the target, and instead go ahead and delete all threads
- of the process but one that reported the event. Note this must
+ of the process but the one that reported the event. Note this must
be done before calling update_breakpoints_after_exec, as
otherwise clearing the threads' resources would reference stale
thread breakpoints -- it may have been one of these threads that
diff --git a/gdb/linux-nat.c b/gdb/linux-nat.c
index 68816ddc999..90ac94440b8 100644
--- a/gdb/linux-nat.c
+++ b/gdb/linux-nat.c
@@ -2001,6 +2001,21 @@ linux_handle_extended_wait (struct lwp_info *lp, int status)
thread execs, it changes its tid to the tgid, and the old
tgid thread might have not been resumed. */
lp->resumed = 1;
+
+ /* All other LWPs are gone now. We'll have received a thread
+ exit notification for all threads other the execing one.
+ That one, if it wasn't the leader, just silently changes its
+ tid to the tgid, and the previous leader vanishes. Since
+ Linux 3.0, the former thread ID can be retrieved with
+ PTRACE_GETEVENTMSG, but since we support older kernels, don't
+ bother with it, and just walk the LWP list. Even with
+ PTRACE_GETEVENTMSG, we'd still need to lookup the
+ corresponding LWP object, and it would be an extra ptrace
+ syscall, so this way may even be more efficient. */
+ for (lwp_info *other_lp : all_lwps_safe ())
+ if (other_lp != lp && other_lp->ptid.pid () == lp->ptid.pid ())
+ exit_lwp (other_lp);
+
return 0;
}

diff --git a/gdb/testsuite/gdb.threads/threads-after-exec.exp b/gdb/testsuite/gdb.threads/threads-after-exec.exp
new file mode 100644
index 00000000000..824dda349a6
--- /dev/null
+++ b/gdb/testsuite/gdb.threads/threads-after-exec.exp
@@ -0,0 +1,70 @@
+# Copyright 2023 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/>.
+
+# Test that after an exec of a non-leader thread, we don't leave the
+# non-leader thread listed in internal thread lists, causing problems.
+
+standard_testfile .c -execd.c
+
+proc do_test { } {
+ global srcdir subdir srcfile srcfile2 binfile testfile
+ global decimal
+
+ # Compile main binary (the one that does the exec).
+ if {[gdb_compile_pthreads $srcdir/$subdir/$srcfile $binfile \
+ executable {debug}] != "" } {
+ return -1
+ }
+
+ # Compile the second binary (the one that gets exec'd).
+ if {[gdb_compile $srcdir/$subdir/$srcfile2 $binfile-execd \
+ executable {debug}] != "" } {
+ return -1
+ }
+
+ clean_restart $binfile
+
+ if ![runto_main] {
+ return
+ }
+
+ gdb_test "catch exec" "Catchpoint $decimal \\(exec\\)"
+
+ gdb_test "continue" "Catchpoint $decimal .*" "continue until exec"
+
+ # Confirm we only have one thread in the thread list.
+ gdb_test "info threads" "\\* 1\[ \t\]+\[^\r\n\]+.*"
+
+ if {[istarget *-*-linux*] && [gdb_is_target_native]} {
+ # Confirm there's only one LWP in the list as well, and that
+ # it is bound to thread 1.1.
+ set inf_pid [get_inferior_pid]
+ gdb_test_multiple "maint info linux-lwps" "" {
+ -wrap -re "Thread ID *\r\n$inf_pid\.$inf_pid\.0\[ \t\]+1\.1 *" {
+ pass $gdb_test_name
+ }
+ }
+ }
+
+ # Test that GDB is able to kill the inferior. This used to crash
+ # on native Linux as GDB did not dispose of the pre-exec LWP for
+ # the non-leader (and that LWP did not have a matching thread in
+ # the core thread list).
+ gdb_test "with confirm off -- kill" \
+ "\\\[Inferior 1 (.*) killed\\\]" \
+ "kill inferior"
+}
+
+do_test
--
2.36.0