[commit][PATCH 2/3] Initialize last_resume_kind for remote fork child

Don Breazeal
2015-05-28T22:13:01Z

This patch fixes some intermittent test failures in
gdb.base/foll-vfork.exp where a vfork child would be (incorrectly)
resumed when handling the vfork event. In this case the result
was a subsequent event reported to the client side as a SIGTRAP
delivered to the as-yet-unknown child thread.

The new thread was resumed (incorrectly) in linux-low.c when
resume_stopped_resumed_lwps was called from
linux_wait_for_event_filtered after the vfork event had been
handled in handle_extended_wait.

Gdbserver/linux-low.c's add_thread function creates threads with
last_resume_kind == resume_continue by default. This field is
used by resume_stopped_resumed_lwps to decide whether to perform
the resume:

static void
resume_stopped_resumed_lwps (struct inferior_list_entry *entry) {
struct thread_info *thread = (struct thread_info *) entry;
struct lwp_info *lp = get_thread_lwp (thread);

if (lp->stopped
&& !lp->status_pending_p
&& thread->last_resume_kind != resume_stop
&& thread->last_status.kind == TARGET_WAITKIND_IGNORE)
{

So the fix is to make sure to set thread->last_resume_kind to
resume_stop. Here we do that for new fork children in
gdbserver/linux-low.c:handle_extended_wait.

In addition, it seemed prudent to initialize lwp_info.status_pending_p
for the new fork child. I also rearranged the initialization code
so that all of the lwp_info initialization was together, rather than
intermixed with thread_info and process_info initialization.

Tested native, native-gdbserver, native-extended-gdbserver on
x86_64 GNU/Linux.

gdb/gdbserver/

* linux-low.c (handle_extended_wait): Initialize
thread_info.last_resume_kind for new fork children.

---
gdb/gdbserver/ChangeLog | 5 +++++
gdb/gdbserver/linux-low.c | 6 +++++-
2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/gdb/gdbserver/ChangeLog b/gdb/gdbserver/ChangeLog
index 0f30c66..4e4f429 100644
--- a/gdb/gdbserver/ChangeLog
+++ b/gdb/gdbserver/ChangeLog
@@ -1,3 +1,8 @@
+2015-05-28 Don Breazeal <donb@codesourcery.com>
+
+ * linux-low.c (handle_extended_wait): Initialize
+ thread_info.last_resume_kind for new fork children.
+
2015-05-15 Pedro Alves <palves@redhat.com>

* target.h (target_handle_new_gdb_connection): Rewrite using if
diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
index 9f3ea48..d763c66 100644
--- a/gdb/gdbserver/linux-low.c
+++ b/gdb/gdbserver/linux-low.c
@@ -457,6 +457,7 @@ handle_extended_wait (struct lwp_info *event_lwp, int wstat)
struct process_info *parent_proc;
struct process_info *child_proc;
struct lwp_info *child_lwp;
+ struct thread_info *child_thr;
struct target_desc *tdesc;

ptid = ptid_build (new_pid, new_pid, 0);
@@ -479,6 +480,10 @@ handle_extended_wait (struct lwp_info *event_lwp, int wstat)
child_lwp = add_lwp (ptid);
gdb_assert (child_lwp != NULL);
child_lwp->stopped = 1;
+ child_lwp->must_set_ptrace_flags = 1;
+ child_lwp->status_pending_p = 0;
+ child_thr = get_lwp_thread (child_lwp);
+ child_thr->last_resume_kind = resume_stop;
parent_proc = get_thread_process (event_thr);
child_proc->attached = parent_proc->attached;
clone_all_breakpoints (&child_proc->breakpoints,
@@ -488,7 +493,6 @@ handle_extended_wait (struct lwp_info *event_lwp, int wstat)
tdesc = xmalloc (sizeof (struct target_desc));
copy_target_description (tdesc, parent_proc->tdesc);
child_proc->tdesc = tdesc;
- child_lwp->must_set_ptrace_flags = 1;

/* Clone arch-specific process data. */
if (the_low_target.new_fork != NULL)
--
1.8.1.1