[gdbserver] linux-low.c: better starvation avoidance, handle non-stop mode too

This patch applies the same starvation avoidance improvements of the
previous patch to the Linux gdbserver side.

Without this, the test added by the following commit
(gdb.threads/non-stop-fair-events.exp) always fails with time outs.

gdb/gdbserver/
2015-01-09  Pedro Alves  <palves@redhat.com>

	* linux-low.c (step_over_bkpt): Move higher up in the file.
	(handle_extended_wait): Don't store the stop_pc here.
	(get_stop_pc): Adjust comments and rename to ...
	(check_stopped_by_breakpoint): ... this.  Record whether the LWP
	stopped for a software breakpoint or hardware breakpoint.
	(thread_still_has_status_pending_p): New function.
	(status_pending_p_callback): Use
	thread_still_has_status_pending_p.  If the event is no longer
	interesting, resume the LWP.
	(handle_tracepoints): Add assert.
	(maybe_move_out_of_jump_pad): Remove cancel_breakpoints call.
	(wstatus_maybe_breakpoint): New function.
	(cancel_breakpoint): Delete function.
	(check_stopped_by_watchpoint): New function, factored out from
	linux_low_filter_event.
	(lp_status_maybe_breakpoint): Delete function.
	(linux_low_filter_event): Remove filter_ptid argument.
	Leave thread group exits pending here.	Store the LWP's stop PC.
	Always leave events pending.
	(linux_wait_for_event_filtered): Pull all events out of the
	kernel, and leave them all pending.
	(count_events_callback, select_event_lwp_callback): Consider all
	events.
	(cancel_breakpoints_callback, linux_cancel_breakpoints): Delete.
	(select_event_lwp): Only give preference to the stepping LWP in
	all-stop mode.	Adjust comments.
	(ignore_event): New function.
	(linux_wait_1): Delete 'retry' label.  Use ignore_event.  Remove
	references to cancel_breakpoints.  Adjust to renames.  Also give
	equal priority to all LWPs that have had events in non-stop mode.
	If reporting a software breakpoint event, unadjust the LWP's PC.
	(linux_wait): If linux_wait_1 returned an ignored event, retry.
	(stuck_in_jump_pad_callback, move_out_of_jump_pad_callback):
	Adjust.
	(linux_resume_one_lwp): Store the LWP's PC.  Adjust.
	(resume_status_pending_p): Use thread_still_has_status_pending_p.
	(linux_stopped_by_watchpoint): Adjust.
	(linux_target_ops): Remove reference to linux_cancel_breakpoints.
	* linux-low.h (enum lwp_stop_reason): New.
	(struct lwp_info) <stop_pc>: Adjust comment.
	<stopped_by_watchpoint>: Delete field.
	<stop_reason>: New field.
	* linux-x86-low.c (x86_linux_prepare_to_resume): Adjust.
	* mem-break.c (software_breakpoint_inserted_here)
	(hardware_breakpoint_inserted_here): New function.
	* mem-break.h (software_breakpoint_inserted_here)
	(hardware_breakpoint_inserted_here): Declare.
	* target.h (struct target_ops) <cancel_breakpoints>: Remove field.
	(cancel_breakpoints): Delete.
	* tracepoint.c (clear_installed_tracepoints, stop_tracing)
	(upload_fast_traceframes): Remove references to
	cancel_breakpoints.

1 files changed, 24 insertions, 5 deletions

diff --git a/gdb/gdbserver/linux-low.h b/gdb/gdbserver/linux-low.h
index 97b163f..bea4a37 100644
--- a/gdb/gdbserver/linux-low.h
+++ b/gdb/gdbserver/linux-low.h
@@ -230,6 +230,24 @@ extern struct linux_target_ops the_low_target;
 #define get_thread_lwp(thr) ((struct lwp_info *) (inferior_target_data (thr)))
 #define get_lwp_thread(lwp) ((lwp)->thread)
 
+/* Reasons an LWP last stopped.  */
+
+enum lwp_stop_reason
+{
+  /* Either not stopped, or stopped for a reason that doesn't require
+     special tracking.  */
+  LWP_STOPPED_BY_NO_REASON,
+
+  /* Stopped by a software breakpoint.  */
+  LWP_STOPPED_BY_SW_BREAKPOINT,
+
+  /* Stopped by a hardware breakpoint.  */
+  LWP_STOPPED_BY_HW_BREAKPOINT,
+
+  /* Stopped by a watchpoint.  */
+  LWP_STOPPED_BY_WATCHPOINT
+};
+
 /* This struct is recorded in the target_data field of struct thread_info.
 
    On linux ``all_threads'' is keyed by the LWP ID, which we use as the
@@ -269,8 +287,9 @@ struct lwp_info
   /* When stopped is set, the last wait status recorded for this lwp.  */
   int last_status;
 
-  /* When stopped is set, this is where the lwp stopped, with
-     decr_pc_after_break already accounted for.  */
+  /* When stopped is set, this is where the lwp last stopped, with
+     decr_pc_after_break already accounted for.  If the LWP is
+     running, this is the address at which the lwp was resumed.  */
   CORE_ADDR stop_pc;
 
   /* If this flag is set, STATUS_PENDING is a waitstatus that has not yet
@@ -278,9 +297,9 @@ struct lwp_info
   int status_pending_p;
   int status_pending;
 
-  /* STOPPED_BY_WATCHPOINT is non-zero if this LWP stopped with a data
-     watchpoint trap.  */
-  int stopped_by_watchpoint;
+  /* The reason the LWP last stopped, if we need to track it
+     (breakpoint, watchpoint, etc.)  */
+  enum lwp_stop_reason stop_reason;
 
   /* On architectures where it is possible to know the data address of
      a triggered watchpoint, STOPPED_DATA_ADDRESS is non-zero, and