Re: [PATCH 2/3] skip_prolgoue (amd64)

[Yao Qi <yao at codesourcery dot com>]

On 12/09/2013 11:34 PM, Pedro Alves wrote:
>> "wait -> handle event -> wait" is like a loop or circle to me, and we
>> >can flush at any point(s) of this circle, depending on what heuristic
>> >we are using.
> Again, the point is making it so that the cache does not enlarge
> the race window with the inferior itself.  IOW, make the cache
> transparent WRT to chances of seeing a teared value, prologue, or
> whatever.  Between starting to handle an event and finishing
> it, a very short time passes.  Between finishing handling an
> event and the next event, an unbound amount of time passes.
> If we don't flush the cache just before handling the event,
> having the cache active has a much much wider race window width
> than without the cache active.

OK, I am convinced.  Here is the patch to flush cache in every
"overlay_cache_invalid = 1" place.  Beside this, I also invalidate
both target cache and overlay cache in infrun_thread_stop_requested_callback,
because handle_inferior_event is called in it.

-- 
Yao (éå)

gdb:

2013-12-10  Yao Qi  <yao@codesourcery.com>

	* infrun.c: Include "target-dcache.h".
	(prepare_for_detach): Call target_dcache_invalidate.
	(wait_for_inferior): Likewise.
	(fetch_inferior_event): Likewise.
	(infrun_thread_stop_requested_callback): Likewise.  Set
	overlay_cache_invalid to 1.
---
 gdb/infrun.c |   24 ++++++++++++++++++++++++
 1 files changed, 24 insertions(+), 0 deletions(-)

diff --git a/gdb/infrun.c b/gdb/infrun.c
index 3b55583..d8f9787 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -60,6 +60,7 @@
 #include "objfiles.h"
 #include "completer.h"
 #include "target-descriptions.h"
+#include "target-dcache.h"
 
 /* Prototypes for local functions */
 
@@ -2475,6 +2476,13 @@ infrun_thread_stop_requested_callback (struct thread_info *info, void *arg)
 
       old_chain = make_cleanup_restore_current_thread ();
 
+      overlay_cache_invalid = 1;
+      /* Flush target cache before starting to handle each event.
+	 Target was running and cache could be stale.  This is just a
+	 heuristic.  Running threads may modify target memory, but we
+	 don't get any event.  */
+      target_dcache_invalidate ();
+
       /* Go through handle_inferior_event/normal_stop, so we always
 	 have consistent output as if the stop event had been
 	 reported.  */
@@ -2677,6 +2685,11 @@ prepare_for_detach (void)
       memset (ecs, 0, sizeof (*ecs));
 
       overlay_cache_invalid = 1;
+      /* Flush target cache before starting to handle each event.
+	 Target was running and cache could be stale.  This is just a
+	 heuristic.  Running threads may modify target memory, but we
+	 don't get any event.  */
+      target_dcache_invalidate ();
 
       if (deprecated_target_wait_hook)
 	ecs->ptid = deprecated_target_wait_hook (pid_ptid, &ecs->ws, 0);
@@ -2740,6 +2753,12 @@ wait_for_inferior (void)
 
       overlay_cache_invalid = 1;
 
+      /* Flush target cache before starting to handle each event.
+	 Target was running and cache could be stale.  This is just a
+	 heuristic.  Running threads may modify target memory, but we
+	 don't get any event.  */
+      target_dcache_invalidate ();
+
       if (deprecated_target_wait_hook)
 	ecs->ptid = deprecated_target_wait_hook (waiton_ptid, &ecs->ws, 0);
       else
@@ -2805,6 +2824,11 @@ fetch_inferior_event (void *client_data)
     make_cleanup_restore_current_thread ();
 
   overlay_cache_invalid = 1;
+  /* Flush target cache before starting to handle each event.  Target
+     was running and cache could be stale.  This is just a heuristic.
+     Running threads may modify target memory, but we don't get any
+     event.  */
+  target_dcache_invalidate ();
 
   make_cleanup_restore_integer (&execution_direction);
   execution_direction = target_execution_direction ();
-- 
1.7.7.6