On Mon, Feb 8, 2021 at 3:07 PM H.J. Lu via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> When the SHSTK feature is not available or not enabled, RDSSP is a NOP,
> always save and restore shadow stack pointer to support compiling source
> codes, containing __builtin_setjmp and __builtin_longjmp, with different
> -fcf-protection options.
Is that an ABI change for -fno-cf-protection?
> PR target/98997
> * config/i386/i386.md (save_stack_nonlocal): Always save shadow
> stack pointer.
> (restore_stack_nonlocal): Always restore shadow stack pointer.
> (@rdssp<mode>): Make it unconditional.
> (@incssp<mode>): Likewise.
> ---
> gcc/config/i386/i386.md | 150 ++++++++++++++++++----------------------
> 1 file changed, 68 insertions(+), 82 deletions(-)
>
> diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
> index b60784a2908..2510bd8a73d 100644
> --- a/gcc/config/i386/i386.md
> +++ b/gcc/config/i386/i386.md
> @@ -19398,21 +19398,16 @@ (define_expand "save_stack_nonlocal"
> (match_operand 1 "register_operand"))]
> ""
> {
> - rtx stack_slot;
> -
> - if (flag_cf_protection & CF_RETURN)
> - {
> - /* Copy shadow stack pointer to the first slot
> - and stack pointer to the second slot. */
> - rtx ssp_slot = adjust_address (operands[0], word_mode, 0);
> - stack_slot = adjust_address (operands[0], Pmode, UNITS_PER_WORD);
> -
> - rtx reg_ssp = force_reg (word_mode, const0_rtx);
> - emit_insn (gen_rdssp (word_mode, reg_ssp, reg_ssp));
> - emit_move_insn (ssp_slot, reg_ssp);
> - }
> - else
> - stack_slot = adjust_address (operands[0], Pmode, 0);
> + /* Copy shadow stack pointer to the first slot and stack pointer to
> + the second slot. */
> + rtx ssp_slot = adjust_address (operands[0], word_mode, 0);
> + rtx stack_slot = adjust_address (operands[0], Pmode, UNITS_PER_WORD);
> +
> + /* If the SHSTK feature is not available or not enabled, the RDSSP
> + instruction is a NOP and REG_SSP is 0. */
> + rtx reg_ssp = force_reg (word_mode, const0_rtx);
> + emit_insn (gen_rdssp (word_mode, reg_ssp, reg_ssp));
> + emit_move_insn (ssp_slot, reg_ssp);
> emit_move_insn (stack_slot, operands[1]);
> DONE;
> })
> @@ -19422,72 +19417,63 @@ (define_expand "restore_stack_nonlocal"
> (match_operand 1 "memory_operand" ""))]
> ""
> {
> - rtx stack_slot;
> + /* Restore shadow stack pointer from the first slot and stack pointer
> + from the second slot. */
> + rtx ssp_slot = adjust_address (operands[1], word_mode, 0);
> + rtx stack_slot = adjust_address (operands[1], Pmode, UNITS_PER_WORD);
>
> - if (flag_cf_protection & CF_RETURN)
> - {
> - /* Restore shadow stack pointer from the first slot
> - and stack pointer from the second slot. */
> - rtx ssp_slot = adjust_address (operands[1], word_mode, 0);
> - stack_slot = adjust_address (operands[1], Pmode, UNITS_PER_WORD);
> -
> - /* Get the current shadow stack pointer. The code below will check if
> - SHSTK feature is enabled. If it is not enabled the RDSSP instruction
> - is a NOP. */
> - rtx reg_ssp = force_reg (word_mode, const0_rtx);
> - emit_insn (gen_rdssp (word_mode, reg_ssp, reg_ssp));
> -
> - /* Compare through subtraction the saved and the current ssp
> - to decide if ssp has to be adjusted. */
> - reg_ssp = expand_simple_binop (word_mode, MINUS,
> - reg_ssp, ssp_slot,
> - reg_ssp, 1, OPTAB_DIRECT);
> -
> - /* Compare and jump over adjustment code. */
> - rtx noadj_label = gen_label_rtx ();
> - emit_cmp_and_jump_insns (reg_ssp, const0_rtx, EQ, NULL_RTX,
> - word_mode, 1, noadj_label);
> -
> - /* Compute the number of frames to adjust. */
> - rtx reg_adj = gen_lowpart (ptr_mode, reg_ssp);
> - rtx reg_adj_neg = expand_simple_unop (ptr_mode, NEG, reg_adj,
> - NULL_RTX, 1);
> -
> - reg_adj = expand_simple_binop (ptr_mode, LSHIFTRT, reg_adj_neg,
> - GEN_INT (exact_log2 (UNITS_PER_WORD)),
> - reg_adj, 1, OPTAB_DIRECT);
> -
> - /* Check if number of frames <= 255 so no loop is needed. */
> - rtx inc_label = gen_label_rtx ();
> - emit_cmp_and_jump_insns (reg_adj, GEN_INT (255), LEU, NULL_RTX,
> - ptr_mode, 1, inc_label);
> -
> - /* Adjust the ssp in a loop. */
> - rtx loop_label = gen_label_rtx ();
> - emit_label (loop_label);
> - LABEL_NUSES (loop_label) = 1;
> -
> - rtx reg_255 = force_reg (word_mode, GEN_INT (255));
> - emit_insn (gen_incssp (word_mode, reg_255));
> -
> - reg_adj = expand_simple_binop (ptr_mode, MINUS,
> - reg_adj, GEN_INT (255),
> - reg_adj, 1, OPTAB_DIRECT);
> -
> - /* Compare and jump to the loop label. */
> - emit_cmp_and_jump_insns (reg_adj, GEN_INT (255), GTU, NULL_RTX,
> - ptr_mode, 1, loop_label);
> -
> - emit_label (inc_label);
> - LABEL_NUSES (inc_label) = 1;
> -
> - emit_insn (gen_incssp (word_mode, reg_ssp));
> -
> - emit_label (noadj_label);
> - LABEL_NUSES (noadj_label) = 1;
> - }
> - else
> - stack_slot = adjust_address (operands[1], Pmode, 0);
> + /* If the SHSTK feature is not available or not enabled, the RDSSP
> + instruction is a NOP and REG_SSP is 0. */
> + rtx reg_ssp = force_reg (word_mode, const0_rtx);
> + emit_insn (gen_rdssp (word_mode, reg_ssp, reg_ssp));
> +
> + /* Compare through subtraction the saved and the current ssp to
> + decide if ssp has to be adjusted. */
> + reg_ssp = expand_simple_binop (word_mode, MINUS, reg_ssp, ssp_slot,
> + reg_ssp, 1, OPTAB_DIRECT);
> +
> + /* Compare and jump over adjustment code. */
> + rtx noadj_label = gen_label_rtx ();
> + emit_cmp_and_jump_insns (reg_ssp, const0_rtx, EQ, NULL_RTX,
> + word_mode, 1, noadj_label);
> +
> + /* Compute the number of frames to adjust. */
> + rtx reg_adj = gen_lowpart (ptr_mode, reg_ssp);
> + rtx reg_adj_neg = expand_simple_unop (ptr_mode, NEG, reg_adj,
> + NULL_RTX, 1);
> +
> + reg_adj = expand_simple_binop (ptr_mode, LSHIFTRT, reg_adj_neg,
> + GEN_INT (exact_log2 (UNITS_PER_WORD)),
> + reg_adj, 1, OPTAB_DIRECT);
> +
> + /* Check if number of frames <= 255 so no loop is needed. */
> + rtx inc_label = gen_label_rtx ();
> + emit_cmp_and_jump_insns (reg_adj, GEN_INT (255), LEU, NULL_RTX,
> + ptr_mode, 1, inc_label);
> +
> + /* Adjust the ssp in a loop. */
> + rtx loop_label = gen_label_rtx ();
> + emit_label (loop_label);
> + LABEL_NUSES (loop_label) = 1;
> +
> + rtx reg_255 = force_reg (word_mode, GEN_INT (255));
> + emit_insn (gen_incssp (word_mode, reg_255));
> +
> + reg_adj = expand_simple_binop (ptr_mode, MINUS,
> + reg_adj, GEN_INT (255),
> + reg_adj, 1, OPTAB_DIRECT);
> +
> + /* Compare and jump to the loop label. */
> + emit_cmp_and_jump_insns (reg_adj, GEN_INT (255), GTU, NULL_RTX,
> + ptr_mode, 1, loop_label);
> +
> + emit_label (inc_label);
> + LABEL_NUSES (inc_label) = 1;
> +
> + emit_insn (gen_incssp (word_mode, reg_ssp));
> +
> + emit_label (noadj_label);
> + LABEL_NUSES (noadj_label) = 1;
> emit_move_insn (operands[0], stack_slot);
> DONE;
> })
> @@ -21455,7 +21441,7 @@ (define_insn "@rdssp<mode>"
> [(set (match_operand:SWI48 0 "register_operand" "=r")
> (unspec_volatile:SWI48 [(match_operand:SWI48 1 "register_operand"
> "0")]
> UNSPECV_NOP_RDSSP))]
> - "TARGET_SHSTK || (flag_cf_protection & CF_RETURN)"
> + ""
> "rdssp<mskmodesuffix>\t%0"
> [(set_attr "length" "6")
> (set_attr "type" "other")])
> @@ -21463,7 +21449,7 @@ (define_insn "@rdssp<mode>"
> (define_insn "@incssp<mode>"
> [(unspec_volatile [(match_operand:SWI48 0 "register_operand" "r")]
> UNSPECV_INCSSP)]
> - "TARGET_SHSTK || (flag_cf_protection & CF_RETURN)"
> + ""
> "incssp<mskmodesuffix>\t%0"
> [(set_attr "length" "4")
> (set_attr "type" "other")])
> --
> 2.29.2
>
