On Sun, Sep 17, 2017 at 10:21:23PM +0930, Alan Modra wrote:
> When -fstack-protector-all or -fsanitize=address, rs6000.h sets
> FRAME_GROWS_DOWNWARD. This breaks the assumption in
> rs6000_return_addr that the stack link is at frame_pointer+0.
Well, builtin_return_address(N) already works correctly for N>0, getting
the backlink via the frame pointer; it's fetching the return address via
the frame pointer that doesn't work.
Okay for trunk (and backports later) with those comments fixed. Thanks!
Segher
> 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.
>
> diff --git a/gcc/config/rs6000/rs6000.c b/gcc/config/rs6000/rs6000.c
> index e611c45..f14392d 100644
> --- a/gcc/config/rs6000/rs6000.c
> +++ b/gcc/config/rs6000/rs6000.c
> @@ -24988,24 +24988,23 @@ 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;
