[PATCH 03/16 v2] Refactor ptrace extended event status

[Don Breazeal <donb at codesourcery dot com>]

This patch implements functions for identifying and extracting extended
ptrace event information from a Linux wait status.  These are just
convenience functions intended to hide the ">> 16" used to extract the
event from the wait status word, replacing the hard-coded shift with a more
descriptive function call.  This is preparatory work for implementation of
follow-fork and detach-on-fork for extended-remote linux targets.

The functions linux_is_extended_waitstatus and
linux_ptrace_get_extended_event are defined in nat/linux-ptrace.c, and
called in linux-nat.c and gdbserver/linux-low.c.  

My initial approach was to implement predicates for every extended event,
e.g. linux_is_traced_clone (status), linux_is_traced_fork (status), but 
that didn't fit the current implementation as well, bloated the code a bit,
and didn't add anything to readability, so I went with just extracting the
event bits from the status instead.

Tested on x64 Ubuntu Lucid, native only.

Thanks
--Don

gdb/
2014-08-20  Don Breazeal  <donb@codesourcery.com>

	* linux-nat.c (linux_handle_extended_wait): Call
	linux_ptrace_get_extended_event.
	(wait_lwp): Call linux_is_extended_waitstatus.
	(linux_nat_filter_event): Call linux_ptrace_get_extended_event
	and linux_is_extended_waitstatus.
	* nat/linux-ptrace.c (linux_test_for_tracefork): Call
	linux_ptrace_get_extended_event.
	(linux_ptrace_get_extended_event): New function.
	(linux_is_extended_waitstatus): New function.
	* nat/linux-ptrace.h: Declare new functions.

gdbserver/
2014-08-20  Don Breazeal  <donb@codesourcery.com>
	* linux-low.c (handle_extended_wait): Call
	linux_ptrace_get_extended_event.
	(get_stop_pc, get_detach_signal, linux_low_filter_event): Call
	linux_is_extended_waitstatus.

---
 gdb/gdbserver/linux-low.c |    8 ++++----
 gdb/linux-nat.c           |   11 +++++++----
 gdb/nat/linux-ptrace.c    |   18 +++++++++++++++++-
 gdb/nat/linux-ptrace.h    |    2 ++
 4 files changed, 30 insertions(+), 9 deletions(-)

diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
index 543987a..dd73c24 100644
--- a/gdb/gdbserver/linux-low.c
+++ b/gdb/gdbserver/linux-low.c
@@ -370,7 +370,7 @@ linux_add_process (int pid, int attached)
 static void
 handle_extended_wait (struct lwp_info *event_child, int wstat)
 {
-  int event = wstat >> 16;
+  int event = linux_ptrace_get_extended_event (wstat);
   struct thread_info *event_thr = get_lwp_thread (event_child);
   struct lwp_info *new_lwp;
 
@@ -512,7 +512,7 @@ get_stop_pc (struct lwp_info *lwp)
   if (WSTOPSIG (lwp->last_status) == SIGTRAP
       && !lwp->stepping
       && !lwp->stopped_by_watchpoint
-      && lwp->last_status >> 16 == 0)
+      && !linux_is_extended_waitstatus (lwp->last_status))
     stop_pc -= the_low_target.decr_pc_after_break;
 
   if (debug_threads)
@@ -1056,7 +1056,7 @@ get_detach_signal (struct thread_info *thread)
     }
 
   /* Extended wait statuses aren't real SIGTRAPs.  */
-  if (WSTOPSIG (status) == SIGTRAP && status >> 16 != 0)
+  if (WSTOPSIG (status) == SIGTRAP && linux_is_extended_waitstatus (status))
     {
       if (debug_threads)
 	debug_printf ("GPS: lwp %s had stopped with extended "
@@ -1869,7 +1869,7 @@ linux_low_filter_event (ptid_t filter_ptid, int lwpid, int wstat)
     }
 
   if (WIFSTOPPED (wstat) && WSTOPSIG (wstat) == SIGTRAP
-      && wstat >> 16 != 0)
+      && linux_is_extended_waitstatus (wstat))
     {
       handle_extended_wait (child, wstat);
       return NULL;
diff --git a/gdb/linux-nat.c b/gdb/linux-nat.c
index ab287bf..1798977 100644
--- a/gdb/linux-nat.c
+++ b/gdb/linux-nat.c
@@ -1800,7 +1800,7 @@ linux_handle_extended_wait (struct lwp_info *lp, int status,
 {
   int pid = ptid_get_lwp (lp->ptid);
   struct target_waitstatus *ourstatus = &lp->waitstatus;
-  int event = status >> 16;
+  int event = linux_ptrace_get_extended_event (status);
 
   if (event == PTRACE_EVENT_FORK || event == PTRACE_EVENT_VFORK
       || event == PTRACE_EVENT_CLONE)
@@ -2164,7 +2164,8 @@ wait_lwp (struct lwp_info *lp)
     }
 
   /* Handle GNU/Linux's extended waitstatus for trace events.  */
-  if (WIFSTOPPED (status) && WSTOPSIG (status) == SIGTRAP && status >> 16 != 0)
+  if (WIFSTOPPED (status) && WSTOPSIG (status) == SIGTRAP
+      && linux_is_extended_waitstatus (status))
     {
       if (debug_linux_nat)
 	fprintf_unfiltered (gdb_stdlog,
@@ -2723,6 +2724,7 @@ static struct lwp_info *
 linux_nat_filter_event (int lwpid, int status, int *new_pending_p)
 {
   struct lwp_info *lp;
+  int event = linux_ptrace_get_extended_event (status);
 
   *new_pending_p = 0;
 
@@ -2742,7 +2744,7 @@ linux_nat_filter_event (int lwpid, int status, int *new_pending_p)
      thread changes its tid to the tgid.  */
 
   if (WIFSTOPPED (status) && lp == NULL
-      && (WSTOPSIG (status) == SIGTRAP && status >> 16 == PTRACE_EVENT_EXEC))
+      && (WSTOPSIG (status) == SIGTRAP && event == PTRACE_EVENT_EXEC))
     {
       /* A multi-thread exec after we had seen the leader exiting.  */
       if (debug_linux_nat)
@@ -2786,7 +2788,8 @@ linux_nat_filter_event (int lwpid, int status, int *new_pending_p)
     }
 
   /* Handle GNU/Linux's extended waitstatus for trace events.  */
-  if (WIFSTOPPED (status) && WSTOPSIG (status) == SIGTRAP && status >> 16 != 0)
+  if (WIFSTOPPED (status) && WSTOPSIG (status) == SIGTRAP
+      && linux_is_extended_waitstatus (status))
     {
       if (debug_linux_nat)
 	fprintf_unfiltered (gdb_stdlog,
diff --git a/gdb/nat/linux-ptrace.c b/gdb/nat/linux-ptrace.c
index b4db862..88d29f2 100644
--- a/gdb/nat/linux-ptrace.c
+++ b/gdb/nat/linux-ptrace.c
@@ -421,7 +421,7 @@ linux_test_for_tracefork (int child_pid)
 
   /* Check if we received a fork event notification.  */
   if (ret == child_pid && WIFSTOPPED (status)
-      && status >> 16 == PTRACE_EVENT_FORK)
+      && linux_ptrace_get_extended_event (status) == PTRACE_EVENT_FORK)
     {
       /* We did receive a fork event notification.  Make sure its PID
 	 is reported.  */
@@ -555,3 +555,19 @@ linux_ptrace_set_additional_flags (int flags)
 {
   additional_flags = flags;
 }
+
+/* Extract extended ptrace event from wait status.  */
+
+int
+linux_ptrace_get_extended_event (int wstat)
+{
+  return (wstat >> 16);
+}
+
+/* Determine whether wait status denotes an extended event.  */
+
+int
+linux_is_extended_waitstatus (int wstat)
+{
+  return (linux_ptrace_get_extended_event (wstat) != 0);
+}
diff --git a/gdb/nat/linux-ptrace.h b/gdb/nat/linux-ptrace.h
index 41b3198..31a77cd 100644
--- a/gdb/nat/linux-ptrace.h
+++ b/gdb/nat/linux-ptrace.h
@@ -92,5 +92,7 @@ extern int linux_supports_traceclone (void);
 extern int linux_supports_tracevforkdone (void);
 extern int linux_supports_tracesysgood (void);
 extern void linux_ptrace_set_additional_flags (int);
+extern int linux_ptrace_get_extended_event (int wstat);
+extern int linux_is_extended_waitstatus (int wstat);
 
 #endif /* COMMON_LINUX_PTRACE_H */
-- 
1.7.0.4