[PATCH 00/31] Step over thread clone and thread exit

Pedro Alves
2022-12-12T20:31:15Z

Here's v3 of the series I previously posted here:

https://inbox.sourceware.org/gdb-patches/20220713222433.374898-1-pedro@palves.net/

New in v3:

- Addressed Simon's comments throughout.

- Addressed Tom de Vries' comments: now builds with
--enable-targets=all, and the testcases should work with no glibc
debug info.

- There are a few new patches:

- [PATCH 07/31] enum_flags to_string

Already approved by Simon. The patches that introduce the new
GDB_THREAD_OPTION_XXX option flags make use of this now to
pretty-print the flags.

- [PATCH 16/31] Move deleting thread on TARGET_WAITKIND_THREAD_EXITED to core

This was half done in another patch previously. In v3, it's
been moved to a separate preparatory patch, and in all-stop, we
now delete threads when pending-exits just before we report a
stop to the user.

- [PATCH 31/31] Cancel execution command on thread exit, when stepping, nexting, etc.

The testcase was augmented to better cover all scenarios.

- This series now applies on top of this other series I posted last
week:

[PATCH 0/6] Eliminate infrun_thread_thread_exit observer
https://inbox.sourceware.org/gdb-patches/20221203211338.2264994-1-pedro@palves.net/T/#t

For your convenience, I've pushed this to the
users/palves/step-over-thread-exit-v3 branch.

Here's the series description, updated for v3:

This is a new series that replaces two different series from last
year.

The first is this series Simon and I wrote, here:

[PATCH 00/10] Step over thread exit (PR gdb/27338)
https://sourceware.org/pipermail/gdb-patches/2021-July/180567.html

The other is a series that coincidentally, back then, Andrew posted at
about the same time, and that addressed problems in kind of the mirror
scenario. His patch series was about stepping over clone (creating
new threads), instead of stepping over thread exit:

[PATCH 0/3] Stepping over clone syscall
https://sourceware.org/pipermail/gdb-patches/2021-June/180517.html

My & Simon's solution back then involved adding a new contract between
GDB and GDBserver -- if a thread is single stepping, and it exits, the
server was supposed to report back the thread's exit to GDB. One of
the motivations for this approach was to be able to control the
enablement of thread exit events per thread, to avoid creating
thread-exit event traffic unnecessarily, as done by
target_thread_events()/QThreadEvents.

Andrew's solution involves using the QThreadEvents mechanism, which
tells the server to report thread create and thread exit events for
all threads. This would conflict with the desire to avoid unnecessary
traffic in the step over thread exit series.

The step over clone fixes back then also weren't yet fully complete,
as Andrew's series only addressed inline step overs. Fixing displaced
stepping over clone syscall would still remain broken.

This new series fixes all of stepping over thread exit and clone, for
both of displaced stepping and inline step overs. It:

- Merges both Andrew's and my/Simon's series, and then reworks both
parts in different ways.

- Introduces clone events at the GDB core and remote protocol level.

- Gets rid of the idea of "reporting thread exit if thread is
single-stepping", replaces it by a new mechanism GDB can use to
explicitly enable thread clone and/or thread exit events, and other
events in the future. The old mechanism also only worked when the
remote server supported hardware single-stepping. This new approach
has an advantage of also working on software single-step targets.

- Uses the new clone events to fix displaced stepping over clone
syscalls too.

- Addresses an issue that Andrew alluded to in his series, and that
coincidentally, we/AMD also ran into with AMDGPU debugging --
currently, with "set scheduler-locking on", if you step over a
function that spawns a thread, that thread runs free, for a bit at
least, and then may stop or not, basically in an unspecified manner.

- Addresses Simon's review comments on the original "Step over thread
exit" series referenced above.

- Centralizes "[Thread ...exited]" notifications in core code.

- Cancels next/step/until/etc. commands on thread exit event, like so:

(gdb) n
[Thread 0x7ffff7d89700 (LWP 3961883) exited]
Command aborted, thread exited.
(gdb)

There are documentation changes in the following patches:

[PATCH 23/31] Don't resume new threads if scheduler-locking is in effect
[PATCH 28/31] Document remote clone events, and QThreadOptions packet

... and they have both already been approved by Eli, in v2. (They
haven't changed in v3).

Tested on x86-64 Ubuntu 20.04, native and gdbserver.

Andrew Burgess (1):
Add test for stepping over clone syscall

Pedro Alves (29):
displaced step: pass down target_waitstatus instead of gdb_signal
linux-nat: introduce pending_status_str
gdb/linux: Delete all other LWPs immediately on ptrace exec event
Step over clone syscall w/ breakpoint, TARGET_WAITKIND_THREAD_CLONED
Support clone events in the remote protocol
Avoid duplicate QThreadEvents packets
enum_flags to_string
Thread options & clone events (core + remote)
Thread options & clone events (native Linux)
Thread options & clone events (Linux GDBserver)
gdbserver: Hide and don't detach pending clone children
Remove gdb/19675 kfails (displaced stepping + clone)
all-stop/synchronous RSP support thread-exit events
gdbserver/linux-low.cc: Ignore event_ptid if TARGET_WAITKIND_IGNORE
Move deleting thread on TARGET_WAITKIND_THREAD_EXITED to core
Introduce GDB_THREAD_OPTION_EXIT thread option, fix
step-over-thread-exit
Implement GDB_THREAD_OPTION_EXIT support for Linux GDBserver
Implement GDB_THREAD_OPTION_EXIT support for native Linux
gdb: clear step over information on thread exit (PR gdb/27338)
stop_all_threads: (re-)enable async before waiting for stops
gdbserver: Queue no-resumed event after thread exit
Don't resume new threads if scheduler-locking is in effect
Report thread exit event for leader if reporting thread exit events
Ignore failure to read PC when resuming
gdb/testsuite/lib/my-syscalls.S: Refactor new SYSCALL macro
Document remote clone events, and QThreadOptions packet
inferior::clear_thread_list always silent
Centralize "[Thread ...exited]" notifications
Cancel execution command on thread exit, when stepping, nexting, etc.

Simon Marchi (1):
Testcases for stepping over thread exit syscall (PR gdb/27338)

gdb/NEWS | 27 +
gdb/annotate.c | 4 +-
gdb/breakpoint.c | 4 +-
gdb/displaced-stepping.c | 18 +-
gdb/displaced-stepping.h | 2 +-
gdb/doc/gdb.texinfo | 131 +++-
gdb/fbsd-nat.c | 3 -
gdb/gdbarch-components.py | 6 +-
gdb/gdbarch-gen.h | 10 +-
gdb/gdbarch.c | 4 +-
gdb/gdbthread.h | 38 +-
gdb/inferior.c | 12 +-
gdb/inferior.h | 7 +-
gdb/infrun.c | 615 +++++++++++++++---
gdb/linux-nat.c | 362 ++++++-----
gdb/linux-nat.h | 4 +
gdb/linux-tdep.c | 5 +-
gdb/linux-tdep.h | 2 +-
gdb/mi/mi-interp.c | 8 +-
gdb/netbsd-nat.c | 5 -
gdb/observable.h | 11 +-
gdb/procfs.c | 6 -
gdb/python/py-inferior.c | 4 +-
gdb/remote.c | 264 +++++++-
gdb/rs6000-tdep.c | 4 +-
gdb/target-debug.h | 2 +
gdb/target-delegates.c | 52 ++
gdb/target.c | 16 +
gdb/target.h | 10 +
gdb/target/target.c | 12 +
gdb/target/target.h | 20 +
gdb/target/waitstatus.c | 1 +
gdb/target/waitstatus.h | 31 +-
gdb/testsuite/gdb.base/step-over-syscall.exp | 44 +-
.../gdb.threads/schedlock-new-thread.c | 54 ++
.../gdb.threads/schedlock-new-thread.exp | 67 ++
gdb/testsuite/gdb.threads/step-over-exec.exp | 6 +
...-over-thread-exit-while-stop-all-threads.c | 77 +++
...ver-thread-exit-while-stop-all-threads.exp | 69 ++
.../gdb.threads/step-over-thread-exit.c | 52 ++
.../gdb.threads/step-over-thread-exit.exp | 151 +++++
gdb/testsuite/gdb.threads/stepi-over-clone.c | 90 +++
.../gdb.threads/stepi-over-clone.exp | 392 +++++++++++
gdb/testsuite/lib/my-syscalls.S | 54 +-
gdb/testsuite/lib/my-syscalls.h | 5 +
gdb/thread.c | 71 +-
gdb/unittests/enum-flags-selftests.c | 69 +-
gdb/windows-nat.c | 16 +-
gdbserver/gdbthread.h | 3 +
gdbserver/linux-low.cc | 399 +++++++-----
gdbserver/linux-low.h | 56 +-
gdbserver/remote-utils.cc | 26 +-
gdbserver/server.cc | 158 ++++-
gdbserver/target.cc | 15 +-
gdbserver/target.h | 27 +-
gdbsupport/enum-flags.h | 66 ++
56 files changed, 3043 insertions(+), 624 deletions(-)
create mode 100644 gdb/testsuite/gdb.threads/schedlock-new-thread.c
create mode 100644 gdb/testsuite/gdb.threads/schedlock-new-thread.exp
create mode 100644 gdb/testsuite/gdb.threads/step-over-thread-exit-while-stop-all-threads.c
create mode 100644 gdb/testsuite/gdb.threads/step-over-thread-exit-while-stop-all-threads.exp
create mode 100644 gdb/testsuite/gdb.threads/step-over-thread-exit.c
create mode 100644 gdb/testsuite/gdb.threads/step-over-thread-exit.exp
create mode 100644 gdb/testsuite/gdb.threads/stepi-over-clone.c
create mode 100644 gdb/testsuite/gdb.threads/stepi-over-clone.exp

base-commit: fb699bafb5f23c2fd43d7f20495171b16903b20f
prerequisite-patch-id: 75b36824a7ee067b57a8d8db6016cb57e4d7f620
prerequisite-patch-id: d5bf8b612deed2abf58a48c553178e080347f34d
prerequisite-patch-id: 3f00d1a451bed27d1b1c27174e15eb604d109a44
prerequisite-patch-id: 5c458d627f349446e40114cb5424b42af08c0824
prerequisite-patch-id: d81a20c336a23c79dafd4da3d780033052b3ac28
prerequisite-patch-id: 8cf0c661a601ff3eacfcd26f11e26bcd11cc867d
--
2.36.0