[PATCH] Fixes to Cygwin-specific signal handling

[Jon Turney <jon dot turney at dronecode dot org dot uk>]

Originally by cgf, this patch has been carried in Cygwin's gdb package for a few
years.  I've cleaned it up a bit and revised it for master.

Without this patch, it's impossible to usefully run the testsuite on Cygwin.

gdb/ChangeLog:

2015-04-11  Jon Turney  <jon.turney@dronecode.org.uk>

	* windows-nat.c: Replace have_saved_context with signal_thread_id
	throughout.
	(thread_rec): Don't retrieve context if we have a saved one.
	Ignore 'Invalid Handle' errors.
	(handle_output_debug_string): Mark signal context as not to be
	written to inferior by windows_continue() or windows_resume().
	(get_windows_debug_event): Replace retval with thread_id
	throughout.  Don't clear any saved context.
---
 gdb/ChangeLog     | 11 +++++++++++
 gdb/windows-nat.c | 55 +++++++++++++++++++++++++++++++------------------------
 2 files changed, 42 insertions(+), 24 deletions(-)

diff --git a/gdb/windows-nat.c b/gdb/windows-nat.c
index fd31083..5c191de 100644
--- a/gdb/windows-nat.c
+++ b/gdb/windows-nat.c
@@ -118,8 +118,8 @@ static COORD WINAPI (*GetConsoleFontSize) (HANDLE, DWORD);
 #   define bad_GetModuleFileNameEx bad_GetModuleFileNameExW
 #endif
 
-static int have_saved_context;	/* True if we've saved context from a
-				   cygwin signal.  */
+static DWORD  signal_thread_id;	/* Non-zero thread id if we have a saved
+				   context from a cygwin signal.  */
 static CONTEXT saved_context;	/* Containes the saved context from a
 				   cygwin signal.  */
 
@@ -301,7 +301,8 @@ thread_rec (DWORD id, int get_context)
       {
 	if (!th->suspended && get_context)
 	  {
-	    if (get_context > 0 && id != current_event.dwThreadId)
+	    if (get_context > 0 && id != current_event.dwThreadId
+		&& id != signal_thread_id)
 	      {
 		if (SuspendThread (th->h) == (DWORD) -1)
 		  {
@@ -310,8 +311,11 @@ thread_rec (DWORD id, int get_context)
 		    /* We get Access Denied (5) when trying to suspend
 		       threads that Windows started on behalf of the
 		       debuggee, usually when those threads are just
-		       about to exit.  */
-		    if (err != ERROR_ACCESS_DENIED)
+		       about to exit.
+		       We can get Invalid Handle (6) if the main thread
+		       has exited. */
+		    if (err != ERROR_INVALID_HANDLE
+			&& err != ERROR_ACCESS_DENIED)
 		      warning (_("SuspendThread (tid=0x%x) failed."
 				 " (winerr %u)"),
 			       (unsigned) id, (unsigned) err);
@@ -433,7 +437,7 @@ do_windows_fetch_inferior_registers (struct regcache *regcache, int r)
   if (current_thread->reload_context)
     {
 #ifdef __COPY_CONTEXT_SIZE
-      if (have_saved_context)
+      if (signal_thread_id)
 	{
 	  /* Lie about where the program actually is stopped since
 	     cygwin has informed us that we should consider the signal
@@ -441,7 +445,7 @@ do_windows_fetch_inferior_registers (struct regcache *regcache, int r)
 	     "saved_context.  */
 	  memcpy (&current_thread->context, &saved_context,
 		  __COPY_CONTEXT_SIZE);
-	  have_saved_context = 0;
+	  signal_thread_id = 0;
 	}
       else
 #endif
@@ -849,8 +853,12 @@ handle_output_debug_string (struct target_waitstatus *ourstatus)
 					 &saved_context,
 					 __COPY_CONTEXT_SIZE, &n)
 		   && n == __COPY_CONTEXT_SIZE)
-	    have_saved_context = 1;
-	  current_event.dwThreadId = retval;
+	    {
+	      signal_thread_id = retval;
+	      saved_context.ContextFlags = 0;  /* Don't attempt to call SetThreadContext */
+	    }
+	  else
+	    retval = 0;
 	}
     }
 #endif
@@ -1317,7 +1325,7 @@ get_windows_debug_event (struct target_ops *ops,
   DWORD continue_status, event_code;
   windows_thread_info *th;
   static windows_thread_info dummy_thread_info;
-  int retval = 0;
+  DWORD thread_id = 0;
 
   last_sig = GDB_SIGNAL_0;
 
@@ -1330,7 +1338,6 @@ get_windows_debug_event (struct target_ops *ops,
   event_code = current_event.dwDebugEventCode;
   ourstatus->kind = TARGET_WAITKIND_SPURIOUS;
   th = NULL;
-  have_saved_context = 0;
 
   switch (event_code)
     {
@@ -1348,14 +1355,14 @@ get_windows_debug_event (struct target_ops *ops,
 	      /* Kludge around a Windows bug where first event is a create
 		 thread event.  Caused when attached process does not have
 		 a main thread.  */
-	      retval = fake_create_process ();
-	      if (retval)
+	      thread_id = fake_create_process ();
+	      if (thread_id)
 		saw_create++;
 	    }
 	  break;
 	}
       /* Record the existence of this thread.  */
-      retval = current_event.dwThreadId;
+      thread_id = current_event.dwThreadId;
       th = windows_add_thread (ptid_build (current_event.dwProcessId, 0,
 					 current_event.dwThreadId),
 			     current_event.u.CreateThread.hThread,
@@ -1398,7 +1405,7 @@ get_windows_debug_event (struct target_ops *ops,
 					   current_event.dwThreadId),
 	     current_event.u.CreateProcessInfo.hThread,
 	     current_event.u.CreateProcessInfo.lpThreadLocalBase);
-      retval = current_event.dwThreadId;
+      thread_id = current_event.dwThreadId;
       break;
 
     case EXIT_PROCESS_DEBUG_EVENT:
@@ -1417,7 +1424,7 @@ get_windows_debug_event (struct target_ops *ops,
 	{
 	  ourstatus->kind = TARGET_WAITKIND_EXITED;
 	  ourstatus->value.integer = current_event.u.ExitProcess.dwExitCode;
-	  retval = main_thread_id;
+	  thread_id = main_thread_id;
 	}
       break;
 
@@ -1432,7 +1439,7 @@ get_windows_debug_event (struct target_ops *ops,
       catch_errors (handle_load_dll, NULL, (char *) "", RETURN_MASK_ALL);
       ourstatus->kind = TARGET_WAITKIND_LOADED;
       ourstatus->value.integer = 0;
-      retval = main_thread_id;
+      thread_id = main_thread_id;
       break;
 
     case UNLOAD_DLL_DEBUG_EVENT:
@@ -1445,7 +1452,7 @@ get_windows_debug_event (struct target_ops *ops,
       catch_errors (handle_unload_dll, NULL, (char *) "", RETURN_MASK_ALL);
       ourstatus->kind = TARGET_WAITKIND_LOADED;
       ourstatus->value.integer = 0;
-      retval = main_thread_id;
+      thread_id = main_thread_id;
       break;
 
     case EXCEPTION_DEBUG_EVENT:
@@ -1461,7 +1468,7 @@ get_windows_debug_event (struct target_ops *ops,
 	  continue_status = DBG_EXCEPTION_NOT_HANDLED;
 	  break;
 	case 1:
-	  retval = current_event.dwThreadId;
+	  thread_id = current_event.dwThreadId;
 	  break;
 	case -1:
 	  last_sig = 1;
@@ -1477,7 +1484,7 @@ get_windows_debug_event (struct target_ops *ops,
 		     "OUTPUT_DEBUG_STRING_EVENT"));
       if (saw_create != 1)
 	break;
-      retval = handle_output_debug_string (ourstatus);
+      thread_id = handle_output_debug_string (ourstatus);
       break;
 
     default:
@@ -1491,7 +1498,7 @@ get_windows_debug_event (struct target_ops *ops,
       break;
     }
 
-  if (!retval || saw_create != 1)
+  if (!thread_id || saw_create != 1)
     {
       if (continue_status == -1)
 	windows_resume (ops, minus_one_ptid, 0, 1);
@@ -1501,12 +1508,12 @@ get_windows_debug_event (struct target_ops *ops,
   else
     {
       inferior_ptid = ptid_build (current_event.dwProcessId, 0,
-				  retval);
-      current_thread = th ?: thread_rec (current_event.dwThreadId, TRUE);
+				  thread_id);
+      current_thread = th ?: thread_rec (thread_id, TRUE);
     }
 
 out:
-  return retval;
+  return (int) thread_id;
 }
 
 /* Wait for interesting events to occur in the target process.  */
-- 
2.1.4