libgcc: fix the handling of return address mangling [PR94891]

Mangling, currently only used on AArch64 for return address signing,
is an internal representation that should not be exposed via

  __builtin_return_address return value,
  __builtin_eh_return handler argument,
  _Unwind_DebugHook handler argument.

Note that a mangled address might not even fit into a void *, e.g.
with AArch64 ilp32 ABI the return address is stored as 64bit, so
the mangled return address cannot be accessed via _Unwind_GetPtr.

This patch changes the unwinder hooks as follows:

MD_POST_EXTRACT_ROOT_ADDR is removed: root address comes from
__builtin_return_address which is not mangled.

MD_POST_EXTRACT_FRAME_ADDR is renamed to MD_DEMANGLE_RETURN_ADDR,
it now operates on _Unwind_Word instead of void *, so the hook
should work when return address signing is enabled on AArch64 ilp32.
(But for that __builtin_aarch64_autia1716 should be fixed to operate
on 64bit input instead of a void *.)

MD_POST_FROB_EH_HANDLER_ADDR is removed: it is the responsibility of
__builtin_eh_return to do the mangling if necessary.

2020-07-13  Szabolcs Nagy  <szabolcs.nagy@arm.com>

libgcc/ChangeLog:

	PR target/94891
	* config/aarch64/aarch64-unwind.h (MD_POST_EXTRACT_ROOT_ADDR): Remove.
	(MD_POST_FROB_EH_HANDLER_ADDR): Remove.
	(MD_POST_EXTRACT_FRAME_ADDR): Rename to ...
	(MD_DEMANGLE_RETURN_ADDR): This.
	(aarch64_post_extract_frame_addr): Rename to ...
	(aarch64_demangle_return_addr): This.
	(aarch64_post_frob_eh_handler_addr): Remove.
	* unwind-dw2.c (uw_update_context): Demangle return address.
	(uw_frob_return_addr): Remove.

1 files changed, 8 insertions, 26 deletions

diff --git a/libgcc/unwind-dw2.c b/libgcc/unwind-dw2.c
index 62d4a3d..fe89656 100644
--- a/libgcc/unwind-dw2.c
+++ b/libgcc/unwind-dw2.c
@@ -1538,11 +1538,14 @@ uw_update_context (struct _Unwind_Context *context, _Unwind_FrameState *fs)
     {
       /* Compute the return address now, since the return address column
 	 can change from frame to frame.  */
-      context->ra = __builtin_extract_return_addr
-	(_Unwind_GetPtr (context, fs->retaddr_column));
-#ifdef MD_POST_EXTRACT_FRAME_ADDR
-      context->ra = MD_POST_EXTRACT_FRAME_ADDR (context, fs, context->ra);
+      void *ret_addr;
+#ifdef MD_DEMANGLE_RETURN_ADDR
+      _Unwind_Word ra = _Unwind_GetGR (context, fs->retaddr_column);
+      ret_addr = MD_DEMANGLE_RETURN_ADDR (context, fs, ra);
+#else
+      ret_addr = _Unwind_GetPtr (context, fs->retaddr_column);
 #endif
+      context->ra = __builtin_extract_return_addr (ret_addr);
     }
 }
 
@@ -1577,9 +1580,6 @@ uw_init_context_1 (struct _Unwind_Context *context,
 		   void *outer_cfa, void *outer_ra)
 {
   void *ra = __builtin_extract_return_addr (__builtin_return_address (0));
-#ifdef MD_POST_EXTRACT_ROOT_ADDR
-  ra = MD_POST_EXTRACT_ROOT_ADDR (ra);
-#endif
   _Unwind_FrameState fs;
   _Unwind_SpTmp sp_slot;
   _Unwind_Reason_Code code;
@@ -1616,9 +1616,6 @@ uw_init_context_1 (struct _Unwind_Context *context,
      initialization context, then we can't see it in the given
      call frame data.  So have the initialization context tell us.  */
   context->ra = __builtin_extract_return_addr (outer_ra);
-#ifdef MD_POST_EXTRACT_ROOT_ADDR
-  context->ra = MD_POST_EXTRACT_ROOT_ADDR (context->ra);
-#endif
 }
 
 static void _Unwind_DebugHook (void *, void *)
@@ -1641,21 +1638,6 @@ _Unwind_DebugHook (void *cfa __attribute__ ((__unused__)),
 #endif
 }
 
-/* Frob exception handler's address kept in TARGET before installing into
-   CURRENT context.  */
-
-static inline void *
-uw_frob_return_addr (struct _Unwind_Context *current
-		     __attribute__ ((__unused__)),
-		     struct _Unwind_Context *target)
-{
-  void *ret_addr = __builtin_frob_return_addr (target->ra);
-#ifdef MD_POST_FROB_EH_HANDLER_ADDR
-  ret_addr = MD_POST_FROB_EH_HANDLER_ADDR (current, target, ret_addr);
-#endif
-  return ret_addr;
-}
-
 /* Install TARGET into CURRENT so that we can return to it.  This is a
    macro because __builtin_eh_return must be invoked in the context of
    our caller.  FRAMES is a number of frames to be unwind.
@@ -1667,7 +1649,7 @@ uw_frob_return_addr (struct _Unwind_Context *current
   do									\
     {									\
       long offset = uw_install_context_1 ((CURRENT), (TARGET));		\
-      void *handler = uw_frob_return_addr ((CURRENT), (TARGET));	\
+      void *handler = __builtin_frob_return_addr ((TARGET)->ra);	\
       _Unwind_DebugHook ((TARGET)->cfa, handler);			\
       _Unwind_Frames_Extra (FRAMES);					\
       __builtin_eh_return (offset, handler);				\