[Ada] Handle version 2 of Windows unwinding information structures

2018-05-24  Eric Botcazou  <ebotcazou@adacore.com>

gcc/ada/

	* raise-gcc.c (__gnat_SEH_error_handler): Remove prototype.
	(__gnat_personality_seh0): Adjust and beef up comments, and
	fix formatting throughout.
	(__gnat_adjust_context): Deal minimally with version 2.
	* seh_init.c (__gnat_map_SEH): Fix formatting.
	(_gnat_SEH_error_handler): Adjust comments.
	(__gnat_install_SEH_handler): Fix formatting.

From-SVN: r260659

1 files changed, 50 insertions, 31 deletions

diff --git a/gcc/ada/raise-gcc.c b/gcc/ada/raise-gcc.c
index 05d1a40..7558414 100644
--- a/gcc/ada/raise-gcc.c
+++ b/gcc/ada/raise-gcc.c
@@ -1457,9 +1457,6 @@ __gnat_Unwind_ForcedUnwind (_Unwind_Exception *e ATTRIBUTE_UNUSED,
        (STATUS_USER_DEFINED | ((TYPE) << 24) | GCC_MAGIC)
 #define STATUS_GCC_THROW		GCC_EXCEPTION (0)
 
-EXCEPTION_DISPOSITION __gnat_SEH_error_handler
- (struct _EXCEPTION_RECORD*, void*, struct _CONTEXT*, void*);
-
 struct Exception_Data *
 __gnat_map_SEH (EXCEPTION_RECORD* ExceptionRecord, const char **msg);
 
@@ -1481,22 +1478,30 @@ __gnat_create_machine_occurrence_from_signal_handler (Exception_Id,
 /* Modify the IP value saved in the machine frame.  This is really a kludge,
    that will be removed if we could propagate the Windows exception (and not
    the GCC one).
+
    What is very wrong is that the Windows unwinder will try to decode the
-   instruction at IP, which isn't valid anymore after the adjust.  */
+   instruction at IP, which isn't valid anymore after the adjustment.  */
 
 static void
 __gnat_adjust_context (unsigned char *unw, ULONG64 rsp)
 {
   unsigned int len;
 
-  /* Version = 1, no flags, no prologue.  */
-  if (unw[0] != 1 || unw[1] != 0)
+  /* Version 1 or 2.  */
+  if (unw[0] != 1 && unw[0] != 2)
+    return;
+  /* No flags, no prologue.  */
+  if (unw[1] != 0)
     return;
   len = unw[2];
-  /* No frame pointer.  */
+  /* No frame.  */
   if (unw[3] != 0)
     return;
-  unw += 4;
+  /* ??? Skip the first 2 undocumented opcodes for version 2.  */
+  if (unw[0] == 2)
+    unw += 8;
+  else
+    unw += 4;
   while (len > 0)
     {
       /* Offset in prologue = 0.  */
@@ -1541,9 +1546,7 @@ __gnat_personality_seh0 (PEXCEPTION_RECORD ms_exc, void *this_frame,
 			 PCONTEXT ms_orig_context,
 			 PDISPATCHER_CONTEXT ms_disp)
 {
-  /* Possibly transform run-time errors into Ada exceptions.  As a small
-     optimization, we call __gnat_SEH_error_handler only on non-user
-     exceptions.  */
+  /* Possibly transform run-time errors into Ada exceptions.  */
   if (!(ms_exc->ExceptionCode & STATUS_USER_DEFINED))
     {
       struct Exception_Data *exception;
@@ -1557,13 +1560,21 @@ __gnat_personality_seh0 (PEXCEPTION_RECORD ms_exc, void *this_frame,
 		       + ms_disp->FunctionEntry->EndAddress))
 	{
 	  /* This is a fault in this function.  We need to adjust the return
-	     address before raising the GCC exception.  */
+	     address before raising the GCC exception.  In order to do that,
+	     we need to locate the machine frame that has been pushed onto
+	     the stack in response to the hardware exception, so we will do
+	     a private unwinding from here, i.e. the frame of the personality
+	     routine, up to the frame immediately following the frame of this
+	     function.  This frame corresponds to a dummy prologue which is
+	     never actually executed but instead appears before the real entry
+	     point of an interrupt routine and exists only to provide a place
+	     to simulate the push of a machine frame.  */
 	  CONTEXT context;
 	  PRUNTIME_FUNCTION mf_func = NULL;
 	  ULONG64 mf_imagebase;
 	  ULONG64 mf_rsp = 0;
 
-	  /* Get the context.  */
+	  /* Get the current context.  */
 	  RtlCaptureContext (&context);
 
 	  while (1)
@@ -1574,27 +1585,31 @@ __gnat_personality_seh0 (PEXCEPTION_RECORD ms_exc, void *this_frame,
 	      ULONG64 EstablisherFrame;
 
 	      /* Get function metadata.  */
-	      RuntimeFunction = RtlLookupFunctionEntry
-		(context.Rip, &ImageBase, ms_disp->HistoryTable);
+	      RuntimeFunction
+		= RtlLookupFunctionEntry (context.Rip, &ImageBase,
+					  ms_disp->HistoryTable);
+
+	      /* Stop once we reached the frame of this function.  */
 	      if (RuntimeFunction == ms_disp->FunctionEntry)
 		break;
+
 	      mf_func = RuntimeFunction;
 	      mf_imagebase = ImageBase;
 	      mf_rsp = context.Rsp;
 
-	      if (!RuntimeFunction)
-		{
-		  /* In case of failure, assume this is a leaf function.  */
-		  context.Rip = *(ULONG64 *) context.Rsp;
-		  context.Rsp += 8;
-		}
-	      else
+	      if (RuntimeFunction)
 		{
 		  /* Unwind.  */
 		  RtlVirtualUnwind (0, ImageBase, context.Rip, RuntimeFunction,
 				    &context, &HandlerData, &EstablisherFrame,
 				    NULL);
 		}
+	      else
+		{
+		  /* In case of failure, assume this is a leaf function.  */
+		  context.Rip = *(ULONG64 *) context.Rsp;
+		  context.Rsp += 8;
+		}
 
 	      /* 0 means bottom of the stack.  */
 	      if (context.Rip == 0)
@@ -1603,6 +1618,8 @@ __gnat_personality_seh0 (PEXCEPTION_RECORD ms_exc, void *this_frame,
 		  break;
 		}
 	    }
+
+	  /* If we have found the machine frame, adjust the return address.  */
 	  if (mf_func != NULL)
 	    __gnat_adjust_context
 	      ((unsigned char *)(mf_imagebase + mf_func->UnwindData), mf_rsp);
@@ -1611,16 +1628,16 @@ __gnat_personality_seh0 (PEXCEPTION_RECORD ms_exc, void *this_frame,
       exception = __gnat_map_SEH (ms_exc, &msg);
       if (exception != NULL)
 	{
-	  struct _Unwind_Exception *exc;
+	  /* Directly convert the system exception into a GCC one.
 
-	  /* Directly convert the system exception to a GCC one.
 	     This is really breaking the API, but is necessary for stack size
 	     reasons: the normal way is to call Raise_From_Signal_Handler,
-	     which build the exception and calls _Unwind_RaiseException, which
-	     unwinds the stack and will call this personality routine. But
-	     the Windows unwinder needs about 2KB of stack.  */
-	  exc = __gnat_create_machine_occurrence_from_signal_handler
-	    (exception, msg);
+	     which builds the exception and calls _Unwind_RaiseException,
+	     which unwinds the stack and will call this personality routine.
+	     But the Windows unwinder needs about 2KB of stack.  */
+	  struct _Unwind_Exception *exc
+	    = __gnat_create_machine_occurrence_from_signal_handler (exception,
+								    msg);
 	  memset (exc->private_, 0, sizeof (exc->private_));
 	  ms_exc->ExceptionCode = STATUS_GCC_THROW;
 	  ms_exc->NumberParameters = 1;
@@ -1629,9 +1646,11 @@ __gnat_personality_seh0 (PEXCEPTION_RECORD ms_exc, void *this_frame,
 
     }
 
-  return _GCC_specific_handler (ms_exc, this_frame, ms_orig_context,
-				ms_disp, __gnat_personality_imp);
+  return
+    _GCC_specific_handler (ms_exc, this_frame, ms_orig_context, ms_disp,
+			   __gnat_personality_imp);
 }
+
 #endif /* SEH */
 
 #if !defined (__USING_SJLJ_EXCEPTIONS__)