[PATCH] x86: Restore the frame pointer in word_mode

Uros Bizjak ubizjak@gmail.com
Mon Apr 13 08:41:16 GMT 2020


On Sun, Apr 12, 2020 at 11:28 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> We must restore the frame pointer in word_mode for eh_return epilogues
> since the upper 32 bits of RBP register can have any values.
>
> Tested on Linux/x32 and Linux/x86-64.  OK for master and backport to
> GCC 8/9 branches?
>
> Thanks.
>
> H.J.
> ---
>         PR target/94556
>         * config/i386/i386.c (ix86_expand_epilogue): Restore the frame
>         pointer in word_mode for eh_return epilogues.
> ---
>  gcc/config/i386/i386.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
> index ca3b7dc06c2..f9c8f75b559 100644
> --- a/gcc/config/i386/i386.c
> +++ b/gcc/config/i386/i386.c
> @@ -9052,8 +9052,14 @@ ix86_expand_epilogue (int style)
>               t = plus_constant (Pmode, t, m->fs.fp_offset - UNITS_PER_WORD);
>               emit_insn (gen_rtx_SET (sa, t));
>
> -             t = gen_frame_mem (Pmode, hard_frame_pointer_rtx);
> -             insn = emit_move_insn (hard_frame_pointer_rtx, t);
> +             /* NB: eh_return epilogues must restore the frame pointer
> +                in word_mode since the upper 32 bits of RBP register
> +                can have any values.  */
> +             t = gen_frame_mem (word_mode, hard_frame_pointer_rtx);
> +             rtx frame_reg = hard_frame_pointer_rtx;
> +             if (Pmode != word_mode)
> +               frame_reg = gen_rtx_REG (word_mode, REGNO (frame_reg));
> +             insn = emit_move_insn (frame_reg, t);

I didn't test it myself, but it looks to me that you can use

"rtx frame_reg = gen_rtx_REG (word_mode, HARD_FRAME_POINTER_REGNUM);"

unconditionally, since gen_rtx_REG has some bypass code to return
hard_frame_pointer_rtx when appropriate.

I don't know x32 enough for a functional review, so LGTM with the above change.

Please wait a week before backporting the patch.

Thanks,
Uros.

>               /* Note that we use SA as a temporary CFA, as the return
>                  address is at the proper place relative to it.  We
> @@ -9068,7 +9074,7 @@ ix86_expand_epilogue (int style)
>               add_reg_note (insn, REG_CFA_DEF_CFA,
>                             plus_constant (Pmode, sa, UNITS_PER_WORD));
>               ix86_add_queued_cfa_restore_notes (insn);
> -             add_reg_note (insn, REG_CFA_RESTORE, hard_frame_pointer_rtx);
> +             add_reg_note (insn, REG_CFA_RESTORE, frame_reg);
>               RTX_FRAME_RELATED_P (insn) = 1;
>
>               m->fs.cfa_reg = sa;
> --
> 2.25.2
>


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