Re: [PATCH 11/31] gdbserver: Hide and don't detach pending clone children

Andrew Burgess via Gdb-patches
2023-06-07T16:11:38Z

Pedro Alves <pedro@palves.net> writes:

> This commit extends the logic added by these two commits from a while
> ago:
>
> #1 7b961964f866 (gdbserver: hide fork child threads from GDB),
> #2 df5ad102009c (gdb, gdbserver: detach fork child when detaching from fork parent)
>
> ... to handle thread clone events, which are very similar to (v)fork
> events.
>
> For #1, we want to hide clone children as well, so just update the
> comments.
>
> For #2, unlike (v)fork children, pending clone children aren't full
> processes, they're just threads, so don't detach them in
> handle_detach. linux-low.cc will take care of detaching them along
> with all other threads of the process, there's nothing special that
> needs to be done.
>
> Change-Id: I7f5901d07efda576a2522d03e183994e071b8ffc
> ---
> gdbserver/linux-low.cc | 5 +++--
> gdbserver/linux-low.h | 36 ++++++++++++++++++++----------------
> gdbserver/server.cc | 12 +++++++-----
> gdbserver/target.cc | 3 ++-
> gdbserver/target.h | 15 ++++++++-------
> 5 files changed, 40 insertions(+), 31 deletions(-)
>
> diff --git a/gdbserver/linux-low.cc b/gdbserver/linux-low.cc
> index d755cda0e44..a7c310260ca 100644
> --- a/gdbserver/linux-low.cc
> +++ b/gdbserver/linux-low.cc
> @@ -6940,9 +6940,10 @@ linux_process_target::thread_pending_parent (thread_info *thread)
> }
>
> thread_info *
> -linux_process_target::thread_pending_child (thread_info *thread)
> +linux_process_target::thread_pending_child (thread_info *thread,
> + target_waitkind *kind)
> {
> - lwp_info *child = get_thread_lwp (thread)->pending_child ();
> + lwp_info *child = get_thread_lwp (thread)->pending_child (kind);
>
> if (child == nullptr)
> return nullptr;
> diff --git a/gdbserver/linux-low.h b/gdbserver/linux-low.h
> index 69a34fb96fc..c9f9db71e09 100644
> --- a/gdbserver/linux-low.h
> +++ b/gdbserver/linux-low.h
> @@ -315,7 +315,8 @@ class linux_process_target : public process_stratum_target
> #endif
>
> thread_info *thread_pending_parent (thread_info *thread) override;
> - thread_info *thread_pending_child (thread_info *thread) override;
> + thread_info *thread_pending_child (thread_info *thread,
> + target_waitkind *kind) override;
>
> bool supports_catch_syscall () override;
>
> @@ -734,8 +735,8 @@ struct pending_signal
>
> struct lwp_info
> {
> - /* If this LWP is a fork child that wasn't reported to GDB yet, return
> - its parent, else nullptr. */
> + /* If this LWP is a fork/vfork/clone child that wasn't reported to
> + GDB yet, return its parent, else nullptr. */
> lwp_info *pending_parent () const
> {
> if (this->fork_relative == nullptr)
> @@ -743,10 +744,10 @@ struct lwp_info
>
> gdb_assert (this->fork_relative->fork_relative == this);
>
> - /* In a fork parent/child relationship, the parent has a status pending and
> - the child does not, and a thread can only be in one such relationship
> - at most. So we can recognize who is the parent based on which one has
> - a pending status. */
> + /* In a parent/child relationship, the parent has a status pending
> + and the child does not, and a thread can only be in one such
> + relationship at most. So we can recognize who is the parent
> + based on which one has a pending status. */
> gdb_assert (!!this->status_pending_p
> != !!this->fork_relative->status_pending_p);
>
> @@ -756,24 +757,25 @@ struct lwp_info
> const target_waitstatus &ws
> = this->fork_relative->waitstatus;
> gdb_assert (ws.kind () == TARGET_WAITKIND_FORKED
> - || ws.kind () == TARGET_WAITKIND_VFORKED);
> + || ws.kind () == TARGET_WAITKIND_VFORKED
> + || ws.kind () == TARGET_WAITKIND_THREAD_CLONED);
>
> return this->fork_relative;
> }
>
> - /* If this LWP is the parent of a fork child we haven't reported to GDB yet,
> - return that child, else nullptr. */
> - lwp_info *pending_child () const
> + /* If this LWP is the parent of a fork/vfork/clone child we haven't
> + reported to GDB yet, return that child, else nullptr. */
> + lwp_info *pending_child (target_waitkind *kind) const
> {
> if (this->fork_relative == nullptr)
> return nullptr;
>
> gdb_assert (this->fork_relative->fork_relative == this);
>
> - /* In a fork parent/child relationship, the parent has a status pending and
> - the child does not, and a thread can only be in one such relationship
> - at most. So we can recognize who is the parent based on which one has
> - a pending status. */
> + /* In a parent/child relationship, the parent has a status pending
> + and the child does not, and a thread can only be in one such
> + relationship at most. So we can recognize who is the parent
> + based on which one has a pending status. */
> gdb_assert (!!this->status_pending_p
> != !!this->fork_relative->status_pending_p);
>
> @@ -782,8 +784,10 @@ struct lwp_info
>
> const target_waitstatus &ws = this->waitstatus;
> gdb_assert (ws.kind () == TARGET_WAITKIND_FORKED
> - || ws.kind () == TARGET_WAITKIND_VFORKED);
> + || ws.kind () == TARGET_WAITKIND_VFORKED
> + || ws.kind () == TARGET_WAITKIND_THREAD_CLONED);
>
> + *kind = ws.kind ();
> return this->fork_relative;
> }
>
> diff --git a/gdbserver/server.cc b/gdbserver/server.cc
> index 5b07c4e4388..07a3319d114 100644
> --- a/gdbserver/server.cc
> +++ b/gdbserver/server.cc
> @@ -1344,8 +1344,9 @@ handle_detach (char *own_buf)
> continue;
>
> /* Only threads that have a pending fork event. */
> - thread_info *child = target_thread_pending_child (thread);
> - if (child == nullptr)
> + target_waitkind kind;
> + thread_info *child = target_thread_pending_child (thread, &kind);
> + if (child == nullptr || kind == TARGET_WAITKIND_THREAD_CLONED)
> continue;
>
> process_info *fork_child_process = get_thread_process (child);
> @@ -1765,9 +1766,10 @@ handle_qxfer_threads_worker (thread_info *thread, struct buffer *buffer)
> gdb_byte *handle;
> bool handle_status = target_thread_handle (ptid, &handle, &handle_len);
>
> - /* If this is a fork or vfork child (has a fork parent), GDB does not yet
> - know about this process, and must not know about it until it gets the
> - corresponding (v)fork event. Exclude this thread from the list. */
> + /* If this is a (v)fork/clone child (has a (v)fork/clone parent),
> + GDB does not yet know about this thread, and must not know about
> + it until it gets the corresponding (v)fork/clone event. Exclude
> + this thread from the list. */
> if (target_thread_pending_parent (thread) != nullptr)
> return;
>
> diff --git a/gdbserver/target.cc b/gdbserver/target.cc
> index 168b843d2ec..4584e9b3a8e 100644
> --- a/gdbserver/target.cc
> +++ b/gdbserver/target.cc
> @@ -814,7 +814,8 @@ process_stratum_target::thread_pending_parent (thread_info *thread)
> }
>
> thread_info *
> -process_stratum_target::thread_pending_child (thread_info *thread)
> +process_stratum_target::thread_pending_child (thread_info *thread,
> + target_waitkind *kind)
> {
> return nullptr;
> }
> diff --git a/gdbserver/target.h b/gdbserver/target.h
> index 8a0d9f42f7d..e2e818b130b 100644
> --- a/gdbserver/target.h
> +++ b/gdbserver/target.h
> @@ -479,13 +479,14 @@ class process_stratum_target
> virtual bool thread_handle (ptid_t ptid, gdb_byte **handle,
> int *handle_len);
>
> - /* If THREAD is a fork child that was not reported to GDB, return its parent
> - else nullptr. */
> + /* If THREAD is a fork/vfork/clone child that was not reported to
> + GDB, return its parent else nullptr. */
> virtual thread_info *thread_pending_parent (thread_info *thread);
>
> - /* If THREAD is the parent of a fork child that was not reported to GDB,
> - return this child, else nullptr. */
> - virtual thread_info *thread_pending_child (thread_info *thread);
> + /* If THREAD is the parent of a fork/vfork/clone child that was not
> + reported to GDB, return this child, else nullptr. */
> + virtual thread_info *thread_pending_child (thread_info *thread,
> + target_waitkind *kind);

Should the comment not say what happens to KIND? I think this comment
applies throughout this patch where KIND was added as an argument.

Otherwise, this looks good.

Reviewed-By: Andrew Burgess <aburgess@redhat.com>

Thanks,
Andrew

>
> /* Returns true if the target can software single step. */
> virtual bool supports_software_single_step ();
> @@ -701,9 +702,9 @@ target_thread_pending_parent (thread_info *thread)
> }
>
> static inline thread_info *
> -target_thread_pending_child (thread_info *thread)
> +target_thread_pending_child (thread_info *thread, target_waitkind *kind)
> {
> - return the_target->thread_pending_child (thread);
> + return the_target->thread_pending_child (thread, kind);
> }
>
> int read_inferior_memory (CORE_ADDR memaddr, unsigned char *myaddr, int len);
> --
> 2.36.0