From d8d96409c83f84f5c15d2e846a7c0a59ceed187c Mon Sep 17 00:00:00 2001 From: Pedro Alves Date: Thu, 17 Mar 2022 19:25:03 +0000 Subject: [PATCH] Introduce GDB_THREAD_OPTION_EXIT thread option, fix step-over-thread-exit When stepping over a breakpoint with displaced stepping, GDB needs to be informed if the stepped thread exits, otherwise the displaced stepping buffer that was allocated to that thread leaks, and this can result in deadlock, with other threads waiting for their turn to displaced step, but their turn never comes. Similarly, when stepping over a breakpoint in line, GDB also needs to be informed if the stepped thread exits, so that is can clear the step over state and re-resume threads. This commit makes it possible for GDB to ask the target to report thread exit events for a given thread, using the new "thread options" mechanism introduced by a previous patch. This only adds the core bits. Following patches in the series will teach the Linux backends (native & gdbserver) to handle the GDB_THREAD_OPTION_EXIT option, and then a later patch will make use of these thread exit events to clean up displaced stepping and inline stepping state properly. Reviewed-By: Andrew Burgess Change-Id: I96b719fdf7fee94709e98bb3a90751d8134f3a38 Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=27338 --- gdb/infrun.c | 15 ++++++++++----- gdb/remote.c | 9 +++++++++ gdb/target/target.c | 1 + gdb/target/target.h | 4 ++++ 4 files changed, 24 insertions(+), 5 deletions(-) diff --git a/gdb/infrun.c b/gdb/infrun.c index e1e761cf48f..0a189d0a485 100644 --- a/gdb/infrun.c +++ b/gdb/infrun.c @@ -2516,24 +2516,29 @@ do_target_resume (ptid_t resume_ptid, bool step, enum gdb_signal sig) else target_pass_signals (signal_pass); - /* Request that the target report thread-{created,cloned} events in - the following situations: + /* Request that the target report thread-{created,cloned,exited} + events in the following situations: - If we are performing an in-line step-over-breakpoint, then we will remove a breakpoint from the target and only run the current thread. We don't want any new thread (spawned by the - step) to start running, as it might miss the breakpoint. + step) to start running, as it might miss the breakpoint. We + need to clear the step-over state if the stepped thread exits, + so we also enable thread-exit events. - If we are stepping over a breakpoint out of line (displaced stepping) then we won't remove a breakpoint from the target, but, if the step spawns a new clone thread, then we will need to fixup the $pc address in the clone child too, so we need it - to start stopped. + to start stopped. We need to release the displaced stepping + buffer if the stepped thread exits, so we also enable + thread-exit events. */ if (step_over_info_valid_p () || displaced_step_in_progress_thread (tp)) { - gdb_thread_options options = GDB_THREAD_OPTION_CLONE; + gdb_thread_options options + = GDB_THREAD_OPTION_CLONE | GDB_THREAD_OPTION_EXIT; if (target_supports_set_thread_options (options)) tp->set_thread_options (options); else diff --git a/gdb/remote.c b/gdb/remote.c index eb537fc48a5..ce5addade6f 100644 --- a/gdb/remote.c +++ b/gdb/remote.c @@ -4206,6 +4206,15 @@ remote_target::update_thread_list () if (has_single_non_exited_thread (tp->inf)) continue; + /* Do not remove the thread if we've requested to be + notified of its exit. For example, the thread may be + displaced stepping, infrun will need to handle the + exit event, and displaced stepping info is recorded + in the thread object. If we deleted the thread now, + we'd lose that info. */ + if ((tp->thread_options () & GDB_THREAD_OPTION_EXIT) != 0) + continue; + /* Not found. */ delete_thread (tp); } diff --git a/gdb/target/target.c b/gdb/target/target.c index 3af7d73df5a..58d0f63c872 100644 --- a/gdb/target/target.c +++ b/gdb/target/target.c @@ -196,6 +196,7 @@ to_string (gdb_thread_options options) { static constexpr gdb_thread_options::string_mapping mapping[] = { MAP_ENUM_FLAG (GDB_THREAD_OPTION_CLONE), + MAP_ENUM_FLAG (GDB_THREAD_OPTION_EXIT), }; return options.to_string (mapping); } diff --git a/gdb/target/target.h b/gdb/target/target.h index 2691f92e4ef..bad4daa22a1 100644 --- a/gdb/target/target.h +++ b/gdb/target/target.h @@ -34,6 +34,10 @@ enum gdb_thread_option : unsigned /* Tell the target to report TARGET_WAITKIND_THREAD_CLONED events for the thread. */ GDB_THREAD_OPTION_CLONE = 1 << 0, + + /* Tell the target to report TARGET_WAITKIND_THREAD_EXIT events for + the thread. */ + GDB_THREAD_OPTION_EXIT = 1 << 1, }; DEF_ENUM_FLAGS_TYPE (enum gdb_thread_option, gdb_thread_options); -- 2.30.2