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

Pedro Alves
2023-11-13T14:24:21Z

Hi!

I've addressed all the review comments in the remaining patches in the series, and none
required any invasive/design change, so I'm going ahead with merging the final result. I'll
still post the resulting/final v4 series to the list, and of course I'll be happy to
address any comments and will be on the lookout for problems this series might cause.

Pedro Alves

On 2022-12-12 20:30, Pedro Alves wrote:
> 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