gdbserver/win32: Rewrite debug registers handling

Don't use debug_reg_state for both:

 * "intent" - what we want the debug registers to look like

 * "reality" - what/which were the contents of the DR registers when
   the event triggered

Reserve it for the former only, like in the GNU/Linux port.

Otherwise the core x86 debug registers code can get confused if the
inferior itself changes the debug registers since GDB last set them.

This is also a requirement for being able to set watchpoints while the
target is running, if/when we get to it on Windows.  See the big
comment in x86_dr_stopped_data_address.

Seems to me this may also fixes propagating watchpoints to all threads
-- continue_one_thread only calls win32_set_thread_context (what
copies the DR registers to the thread), if something already fetched
the thread's context before.  Something else may be masking this
issue, I haven't checked.

Smoke tested by running gdbserver under Wine, connecting to it from
GNU/Linux, and checking that I could trigger a watchpoint as expected.

Joel tested it on x86-windows using AdaCore's testsuite.

gdb/gdbserver/
2014-10-15  Pedro Alves  <palves@redhat.com>

	PR server/17487
	* win32-arm-low.c (arm_set_thread_context): Remove current_event
	parameter.
	(arm_set_thread_context): Delete.
	(the_low_target): Adjust.
	* win32-i386-low.c (debug_registers_changed)
	(debug_registers_used): Delete.
	(update_debug_registers_callback): New function.
	(x86_dr_low_set_addr, x86_dr_low_set_control): Mark all threads as
	needing to update their debug registers.
	(win32_get_current_dr): New function.
	(x86_dr_low_get_addr, x86_dr_low_get_control)
	(x86_dr_low_get_status): Fetch the debug register from the thread
	record's context.
	(i386_initial_stuff): Adjust.
	(i386_get_thread_context): Remove current_event parameter.  Don't
	clear debug_registers_changed nor copy DR values to
	debug_reg_state.
	(i386_set_thread_context): Delete.
	(i386_prepare_to_resume): New function.
	(i386_thread_added): Mark the thread as needing to update irs
	debug registers.
	(the_low_target): Remove i386_set_thread_context and install
	i386_prepare_to_resume.
	* win32-low.c (win32_get_thread_context): Adjust.
	(win32_set_thread_context): Use SetThreadContext
	directly.
	(win32_prepare_to_resume): New function.
	(win32_require_context): New function, factored out from ...
	(thread_rec): ... this.
	(continue_one_thread): Call win32_prepare_to_resume on each thread
	we're about to continue.
	(win32_resume): Call win32_prepare_to_resume on the event thread.
	* win32-low.h (struct win32_thread_info)
	<debug_registers_changed>: New field.
	(struct win32_target_ops): Change prototype of set_thread_context,
	delete set_thread_context and add prepare_to_resume.
	(win32_require_context): New declaration.

1 files changed, 48 insertions, 25 deletions

diff --git a/gdb/gdbserver/win32-low.c b/gdb/gdbserver/win32-low.c
index ee99fe4126a..e714933eb01 100644
--- a/gdb/gdbserver/win32-low.c
+++ b/gdb/gdbserver/win32-low.c
@@ -129,7 +129,7 @@ static void
 win32_get_thread_context (win32_thread_info *th)
 {
   memset (&th->context, 0, sizeof (CONTEXT));
-  (*the_low_target.get_thread_context) (th, &current_event);
+  (*the_low_target.get_thread_context) (th);
 #ifdef _WIN32_WCE
   memcpy (&th->base_context, &th->context, sizeof (CONTEXT));
 #endif
@@ -153,23 +153,24 @@ win32_set_thread_context (win32_thread_info *th)
      it between stopping and resuming.  */
   if (memcmp (&th->context, &th->base_context, sizeof (CONTEXT)) != 0)
 #endif
-    (*the_low_target.set_thread_context) (th, &current_event);
+    SetThreadContext (th->h, &th->context);
 }
 
-/* Find a thread record given a thread id.  If GET_CONTEXT is set then
-   also retrieve the context for this thread.  */
-static win32_thread_info *
-thread_rec (ptid_t ptid, int get_context)
+/* Set the thread context of the thread associated with TH.  */
+
+static void
+win32_prepare_to_resume (win32_thread_info *th)
 {
-  struct thread_info *thread;
-  win32_thread_info *th;
+  if (the_low_target.prepare_to_resume != NULL)
+    (*the_low_target.prepare_to_resume) (th);
+}
 
-  thread = (struct thread_info *) find_inferior_id (&all_threads, ptid);
-  if (thread == NULL)
-    return NULL;
+/* See win32-low.h.  */
 
-  th = inferior_target_data (thread);
-  if (get_context && th->context.ContextFlags == 0)
+void
+win32_require_context (win32_thread_info *th)
+{
+  if (th->context.ContextFlags == 0)
     {
       if (!th->suspended)
 	{
@@ -185,7 +186,23 @@ thread_rec (ptid_t ptid, int get_context)
 
       win32_get_thread_context (th);
     }
+}
 
+/* Find a thread record given a thread id.  If GET_CONTEXT is set then
+   also retrieve the context for this thread.  */
+static win32_thread_info *
+thread_rec (ptid_t ptid, int get_context)
+{
+  struct thread_info *thread;
+  win32_thread_info *th;
+
+  thread = (struct thread_info *) find_inferior_id (&all_threads, ptid);
+  if (thread == NULL)
+    return NULL;
+
+  th = inferior_target_data (thread);
+  if (get_context)
+    win32_require_context (th);
   return th;
 }
 
@@ -419,22 +436,26 @@ continue_one_thread (struct inferior_list_entry *this_thread, void *id_ptr)
   int thread_id = * (int *) id_ptr;
   win32_thread_info *th = inferior_target_data (thread);
 
-  if ((thread_id == -1 || thread_id == th->tid)
-      && th->suspended)
+  if (thread_id == -1 || thread_id == th->tid)
     {
-      if (th->context.ContextFlags)
-	{
-	  win32_set_thread_context (th);
-	  th->context.ContextFlags = 0;
-	}
+      win32_prepare_to_resume (th);
 
-      if (ResumeThread (th->h) == (DWORD) -1)
+      if (th->suspended)
 	{
-	  DWORD err = GetLastError ();
-	  OUTMSG (("warning: ResumeThread failed in continue_one_thread, "
-		   "(error %d): %s\n", (int) err, strwinerror (err)));
+	  if (th->context.ContextFlags)
+	    {
+	      win32_set_thread_context (th);
+	      th->context.ContextFlags = 0;
+	    }
+
+	  if (ResumeThread (th->h) == (DWORD) -1)
+	    {
+	      DWORD err = GetLastError ();
+	      OUTMSG (("warning: ResumeThread failed in continue_one_thread, "
+		       "(error %d): %s\n", (int) err, strwinerror (err)));
+	    }
+	  th->suspended = 0;
 	}
-      th->suspended = 0;
     }
 
   return 0;
@@ -937,6 +958,8 @@ win32_resume (struct thread_resume *resume_info, size_t n)
   th = thread_rec (ptid, FALSE);
   if (th)
     {
+      win32_prepare_to_resume (th);
+
       if (th->context.ContextFlags)
 	{
 	  /* Move register values from the inferior into the thread