regrename/i386: ROP vs df and stack-regs

[Bernd Schmidt <bschmidt at redhat dot com>]

This is a patch for PRs 68471 and 68472, which show problems with the 
ROP mitigation:
 * reg-stack doesn't call df_insn_update when it makes changes, and
   if df checking is enabled, any subsequent df_analyze call will
   abort
 * Using -mcmodel=medium fails because of a pattern that has lea type
   and needs its modrm_class overridden.

Both of these are fixed in the i386 backend. As a further safety 
measure, I've added some extra code to regrename to ignore stack regs 
after regstack_complete - they can't be dealt with anymore.

Bootstrapped and tested on x86_64-linux, with -mmitigate-rop forced on. Ok?


Bernd

	PR target/68471
	PR target/68472
	* config/i386/i386.c (ix86_mitigate_rop): Don't call
	compute_bb_for_insn again.  Call df_insn_rescan_all.
	* config/i386/i386.md (set_got_rex64): Override modrm_class.

	* regrename.c (build_def_use): Ignore stack regs if regstack_completed.

testsuite/
	* gcc.target/i386/rop1.c: New test.

diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
index 2ac6c25..14c99eb 100644
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -45243,8 +45243,9 @@ ix86_mitigate_rop (void)
   COPY_HARD_REG_SET (inout_risky, input_risky);
   IOR_HARD_REG_SET (inout_risky, output_risky);
 
-  compute_bb_for_insn ();
   df_note_add_problem ();
+  /* Fix up what stack-regs did.  */
+  df_insn_rescan_all ();
   df_analyze ();
 
   regrename_init (true);
diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
index a57d165..671580d 100644
--- a/gcc/config/i386/i386.md
+++ b/gcc/config/i386/i386.md
@@ -12418,6 +12418,7 @@
   "lea{q}\t{_GLOBAL_OFFSET_TABLE_(%%rip), %0|%0, _GLOBAL_OFFSET_TABLE_[rip]}"
   [(set_attr "type" "lea")
    (set_attr "length_address" "4")
+   (set_attr "modrm_class" "unknown")
    (set_attr "mode" "DI")])
 
 (define_insn "set_rip_rex64"
diff --git a/gcc/regrename.c b/gcc/regrename.c
index e2a1e83..47c8dfa 100644
--- a/gcc/regrename.c
+++ b/gcc/regrename.c
@@ -1685,6 +1685,13 @@ build_def_use (basic_block bb)
 		  && !verify_reg_tracked (op))
 		create_new_chain (REGNO (op), REG_NREGS (op), NULL, NULL,
 				  NO_REGS);
+#ifdef STACK_REGS
+	      if (regstack_completed
+		  && REG_P (recog_data.operand[i])
+		  && IN_RANGE (REGNO (recog_data.operand[i]),
+			       FIRST_STACK_REG, LAST_STACK_REG))
+		untracked_operands |= 1 << i;
+#endif
 	    }
 
 	  if (fail_current_block)
--- /dev/null	2015-11-23 12:05:22.553607702 +0100
+++ gcc/testsuite/gcc.target/i386/rop1.c	2015-11-24 15:40:04.381086953 +0100
@@ -0,0 +1,7 @@
+/* { dg-do compile } */
+/* { dg-require-effective-target lp64 } */
+/* { dg-options "-mcmodel=medium -mmitigate-rop" } */
+void
+foo (void)
+{
+}