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i386: Rewrite restore_stack_nonlocal expander [PR96536].

Browse Source 
-fcf-protection code in restore_stack_nonlocal uses a branch based on
a clobber result.  The patch adds missing compare and completely
rewrites the expander to use high-level functions in RTL construction.

2020-08-18  Uroš Bizjak  <ubizjak@gmail.com>

gcc/ChangeLog:

	PR target/96536
	* config/i386/i386.md (restore_stack_nonlocal): Add missing compare
	RTX.  Rewrite expander to use high-level functions in RTL construction.
This commit is contained in:
Uros Bizjak 2020-08-18 17:31:49 +02:00
parent 6c1a58b7fb
commit f8104bb9dc
1 changed files with 41 additions and 70 deletions
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111
gcc/config/i386/i386.md
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@ -19112,15 +19112,17 @@
""
{
rtx stack_slot;
if ((flag_cf_protection & CF_RETURN))
if (flag_cf_protection & CF_RETURN)
{
/* Copy shadow stack pointer to the first slot and stack ppointer
to the second slot. */
/* 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 ssp = force_reg (word_mode, const0_rtx);
emit_insn (gen_rdssp (word_mode, ssp, ssp));
emit_move_insn (ssp_slot, ssp);
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);
@ -19134,95 +19136,64 @@
""
{
rtx stack_slot;
if ((flag_cf_protection & CF_RETURN))
if (flag_cf_protection & CF_RETURN)
{
/* Restore shadow stack pointer from the first slot and stack
pointer from the second 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);
stack_slot = adjust_address (operands[1], Pmode, UNITS_PER_WORD);
rtx flags, jump, noadj_label, inc_label, loop_label;
rtx reg_adj, reg_ssp, tmp, clob;
/* 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. */
reg_ssp = force_reg (word_mode, const0_rtx);
rtx reg_ssp = force_reg (word_mode, const0_rtx);
emit_insn (gen_rdssp (word_mode, reg_ssp, reg_ssp));
/* Compare through substraction the saved and the current ssp to decide
if ssp has to be adjusted. */
tmp = gen_rtx_SET (reg_ssp, gen_rtx_MINUS (word_mode, reg_ssp,
ssp_slot));
clob = gen_rtx_CLOBBER (VOIDmode, gen_rtx_REG (CCmode, FLAGS_REG));
tmp = gen_rtx_PARALLEL (VOIDmode, gen_rtvec (2, tmp, clob));
emit_insn (tmp);
/* 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. */
noadj_label = gen_label_rtx ();
flags = gen_rtx_REG (CCZmode, FLAGS_REG);
tmp = gen_rtx_EQ (VOIDmode, flags, const0_rtx);
tmp = gen_rtx_IF_THEN_ELSE (VOIDmode, tmp,
gen_rtx_LABEL_REF (VOIDmode, noadj_label),
pc_rtx);
jump = emit_jump_insn (gen_rtx_SET (pc_rtx, tmp));
JUMP_LABEL (jump) = noadj_label;
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 numebr of frames to adjust. */
reg_adj = gen_lowpart (ptr_mode, reg_ssp);
tmp = gen_rtx_SET (reg_adj,
gen_rtx_LSHIFTRT (ptr_mode,
negate_rtx (ptr_mode, reg_adj),
GEN_INT ((word_mode == SImode)
? 2
: 3)));
clob = gen_rtx_CLOBBER (VOIDmode, gen_rtx_REG (CCmode, FLAGS_REG));
tmp = gen_rtx_PARALLEL (VOIDmode, gen_rtvec (2, tmp, clob));
emit_insn (tmp);
/* 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. */
tmp = gen_rtx_COMPARE (CCmode, reg_adj, GEN_INT (255));
flags = gen_rtx_REG (CCmode, FLAGS_REG);
emit_insn (gen_rtx_SET (flags, tmp));
inc_label = gen_label_rtx ();
tmp = gen_rtx_LEU (VOIDmode, flags, const0_rtx);
tmp = gen_rtx_IF_THEN_ELSE (VOIDmode, tmp,
gen_rtx_LABEL_REF (VOIDmode, inc_label),
pc_rtx);
jump = emit_jump_insn (gen_rtx_SET (pc_rtx, tmp));
JUMP_LABEL (jump) = inc_label;
rtx reg_255 = gen_reg_rtx (word_mode);
emit_move_insn (reg_255, GEN_INT (255));
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. */
loop_label = gen_label_rtx ();
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));
tmp = gen_rtx_SET (reg_adj, gen_rtx_MINUS (ptr_mode,
reg_adj,
GEN_INT (255)));
clob = gen_rtx_CLOBBER (VOIDmode, gen_rtx_REG (CCmode, FLAGS_REG));
tmp = gen_rtx_PARALLEL (VOIDmode, gen_rtvec (2, tmp, clob));
emit_insn (tmp);
tmp = gen_rtx_COMPARE (CCmode, reg_adj, GEN_INT (255));
flags = gen_rtx_REG (CCmode, FLAGS_REG);
emit_insn (gen_rtx_SET (flags, tmp));
reg_adj = expand_simple_binop (ptr_mode, MINUS,
reg_adj, GEN_INT (255),
reg_adj, 1, OPTAB_DIRECT);
/* Jump to the loop label. */
tmp = gen_rtx_GTU (VOIDmode, flags, const0_rtx);
tmp = gen_rtx_IF_THEN_ELSE (VOIDmode, tmp,
gen_rtx_LABEL_REF (VOIDmode, loop_label),
pc_rtx);
jump = emit_jump_insn (gen_rtx_SET (pc_rtx, tmp));
JUMP_LABEL (jump) = loop_label;
/* 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);