[PATCH v2 00/29] Step over thread clone and thread exit
Pedro Alves
pedro@palves.net
Wed Jul 13 22:24:04 GMT 2022
Here's v2 of the series I previously posted here:
https://sourceware.org/pipermail/gdb-patches/2022-June/190181.html
New in v2:
- One patch of v1 made it to master, one was dropped, and there are
a few new patches.
- GDB now clears the (QThreadOptions) thread options of all threads
that are resumed, not just the current thread, in all-stop.
- GDB now coalesces QThreadOptions packets, similarly to how vCont
packets are aggregated. Consequently, target_set_thread_options
disappeared. The need for this was exposed by the previous bullet
point, as in the v1 implementation, setting & clearing the thread
options of all threads led to two QThreadOptions packet per
thread, one when resuming, and another when stopping. Now there's
only one packet per high level, like the vCont packets.
- That exposed a few bugs in gdbserver's implementation of
QThreadOptions, now fixed.
- It also exposed that making fork/vfork/clone threads inherit their
QThreadOptions options from the parent (modeling
PTRACE_SETOPTIONS), was a mistake. By not inheriting, GDB can
send e.g., "QThreadOptions;0;1:TID" without worrying about threads
it doesn't know about yet. Patches that were copying thread
options from parent to child are now simpler, as they no longer do
that.
- GDB now also avoids sending repeated QThreadEvents packets.
- The printing the number of unexpect cores in gdb.sum caught that
one testcase was passing cleanly, with same number of PASSes as
before, but, GDB was crashing during teardown. There's a new
patch to fix the crash, which was a latent problem:
[PATCH v2 03/29] gdb/linux: Delete all other LWPs immediately on ptrace exec event
- The documentation patches in v1 where already reviewed, iterated
on, and largely approved. The documentation changes in v2 are the
result of those reviews/discussions.
- Patch #14 is new:
[PATCH v2 14/29] gdbserver/linux-low.cc: Ignore event_ptid if TARGET_WAITKIND_IGNORE
This fixes a latent issue that gdbserver testing ran into.
- The last 3 patches of the series are also new:
[PATCH v2 27/29] inferior::clear_thread_list always silent
[PATCH v2 28/29] Centralize "[Thread ...exited]" notifications
[PATCH v2 29/29] Cancel execution command on thread exit, when stepping, nexting, etc.
The first two of those are preparatory patches for the last one.
That patch is the last missing piece necessary to make step over
thread exit work nicely on the yet-unsubmitted AMGPU port, but
it's also a nice improvement for normal CPU debugging too, IMO.
- Probably some minor details throughout the series that I forgot to
take notes of.
Here's the series description, updated for v2:
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 envolves 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 21/29] Don't resume new threads if scheduler-locking is in effect
[PATCH 26/29] Document remote clone events, and QThreadOptions packet
... which as mentione above, were already discussed in v1, and updated
accordingly.
I'm aware that Tankut also has patches addressing issues around
reading registers of already-exited processes, but I haven't looked at
them in any detail yet. So I guess patch #23 ("Ignore failure to read
PC when resuming") may end up changing or be replaced by Tankut's.
Tested on x86-64 Ubuntu 20.04, native and gdbserver.
Andrew Burgess (1):
Add test for stepping over clone syscall
Pedro Alves (26):
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
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
Introduce GDB_TO_EXIT thread option, fix step-over-thread-exit
Implement GDB_TO_EXIT support for Linux GDBserver
Implement GDB_TO_EXIT support for native Linux
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 (2):
gdb: clear step over information on thread exit (PR gdb/27338)
Testcases for stepping over thread exit syscall (PR gdb/27338)
gdb/NEWS | 26 +
gdb/annotate.c | 4 +-
gdb/breakpoint.c | 4 +-
gdb/displaced-stepping.c | 18 +-
gdb/displaced-stepping.h | 2 +-
gdb/doc/gdb.texinfo | 130 +++-
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 | 589 +++++++++++++++---
gdb/linux-nat.c | 381 ++++++-----
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 | 4 -
gdb/observable.h | 11 +-
gdb/procfs.c | 6 -
gdb/python/py-inferior.c | 4 +-
gdb/remote.c | 251 +++++++-
gdb/target-debug.h | 2 +
gdb/target-delegates.c | 52 ++
gdb/target.c | 17 +
gdb/target.h | 10 +
gdb/target/target.h | 14 +
gdb/target/waitstatus.c | 1 +
gdb/target/waitstatus.h | 20 +-
gdb/testsuite/gdb.base/step-over-syscall.exp | 44 +-
.../gdb.threads/schedlock-new-thread.c | 46 ++
.../gdb.threads/schedlock-new-thread.exp | 63 ++
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 | 130 ++++
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 | 70 ++-
gdb/windows-nat.c | 16 +-
gdbserver/gdbthread.h | 3 +
gdbserver/linux-low.cc | 401 +++++++-----
gdbserver/linux-low.h | 56 +-
gdbserver/remote-utils.cc | 26 +-
gdbserver/server.cc | 158 ++++-
gdbserver/target.cc | 15 +-
gdbserver/target.h | 30 +-
52 files changed, 2848 insertions(+), 600 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: 9779607aff84cad92d8800290dce4eb17c17ce12
--
2.36.0
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