[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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