PR81996, __builtin_return_address(0) fails

rs6000_return_addr assumes that the stack link is at frame+0, which is
true for count>0.  For count==0, rs6000_return_addr is called with
frame==frame_pointer_rtx and the stack link is *not* at frame+0 if
-fstack-protector-all or -fsanitize=address because rs6000.h sets
FRAME_GROWS_DOWNWARD for those options.

	PR target/81996
	* gcc/config/rs6000/rs6000.c (rs6000_return_addr): Use
	stack_pointer_rtx for count 0.  Update comments.  Break up
	large rtl expression.

From-SVN: r253070

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 9a8afeb3c2674ddb2d068b20f17f8f77ade035e9..ce63706113fc709b475dd04814c8c76547a38da0 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,10 @@
+2017-09-21  Alan Modra  <amodra@gmail.com>
+
+       PR target/81996
+       * gcc/config/rs6000/rs6000.c (rs6000_return_addr): Use
+       stack_pointer_rtx for count 0.  Update comments.  Break up
+       large rtl expression.
+
 2017-09-19  Martin Liska  <mliska@suse.cz>
 
        PR c++/81355

diff --git a/gcc/config/rs6000/rs6000.c b/gcc/config/rs6000/rs6000.c
index 32433b294a0d0c9634e0ea29736455ad17299656..be3912cdb8dc0e07aa901c34790cbe3a23506567 100644 (file)
--- a/gcc/config/rs6000/rs6000.c
+++ b/gcc/config/rs6000/rs6000.c
@@ -22314,24 +22314,23 @@ debug_stack_info (rs6000_stack_t *info)
 rtx
 rs6000_return_addr (int count, rtx frame)
 {
-  /* Currently we don't optimize very well between prolog and body
-     code and for PIC code the code can be actually quite bad, so
-     don't try to be too clever here.  */
+  /* We can't use get_hard_reg_initial_val for LR when count == 0 if LR
+     is trashed by the prologue, as it is for PIC on ABI_V4 and Darwin.  */
   if (count != 0
       || ((DEFAULT_ABI == ABI_V4 || DEFAULT_ABI == ABI_DARWIN) && flag_pic))
     {
       cfun->machine->ra_needs_full_frame = 1;
 
-      return
-       gen_rtx_MEM
-         (Pmode,
-          memory_address
-          (Pmode,
-           plus_constant (Pmode,
-                          copy_to_reg
-                          (gen_rtx_MEM (Pmode,
-                                        memory_address (Pmode, frame))),
-                          RETURN_ADDRESS_OFFSET)));
+      if (count == 0)
+       /* FRAME is set to frame_pointer_rtx by the generic code, but that
+          is good for loading 0(r1) only when !FRAME_GROWS_DOWNWARD.  */
+       frame = stack_pointer_rtx;
+      rtx prev_frame_addr = memory_address (Pmode, frame);
+      rtx prev_frame = copy_to_reg (gen_rtx_MEM (Pmode, prev_frame_addr));
+      rtx lr_save_off = plus_constant (Pmode,
+                                      prev_frame, RETURN_ADDRESS_OFFSET);
+      rtx lr_save_addr = memory_address (Pmode, lr_save_off);
+      return gen_rtx_MEM (Pmode, lr_save_addr);
     }
 
   cfun->machine->ra_need_lr = 1;