Hi!
As discussed in the PR and suggested by Uros, scheduler has code to keep a
use of hard register next to the assignment that sets that hard register
from a pseudo, which is desirable so that RA can deal with it properly.
Unfortunately, with -fstack-protector* we stick the stack protect epilogue
in between, which splits the load and use to different basic blocks.
The code emitted by expand_function_end between these two spots is only the
loading of the return value into registers, so generally it shouldn't
contain any stores which stack protection wants to guard against, so I
believe from security POV this shouldn't weaken anything, but fixes the
testcase.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2019-02-01 Jakub Jelinek <ja...@redhat.com>
PR rtl-optimization/87485
* function.c (expand_function_end): Move stack_protect_epilogue
before loading of return value into hard register(s).
* gcc.dg/pr87485.c: New test.
--- gcc/function.c.jj 2019-01-29 16:47:02.000000000 +0100
+++ gcc/function.c 2019-02-01 16:23:07.471877843 +0100
@@ -5330,6 +5330,10 @@ expand_function_end (void)
communicate between __builtin_eh_return and the epilogue. */
expand_eh_return ();
+ /* If stack protection is enabled for this function, check the guard. */
+ if (crtl->stack_protect_guard && targetm.stack_protect_runtime_enabled_p ())
+ stack_protect_epilogue ();
+
/* If scalar return value was computed in a pseudo-reg, or was a named
return value that got dumped to the stack, copy that to the hard
return register. */
@@ -5475,10 +5479,6 @@ expand_function_end (void)
&& targetm_common.except_unwind_info (&global_options) != UI_SJLJ)
emit_insn (gen_blockage ());
- /* If stack protection is enabled for this function, check the guard. */
- if (crtl->stack_protect_guard && targetm.stack_protect_runtime_enabled_p ())
- stack_protect_epilogue ();
-
/* If we had calls to alloca, and this machine needs
an accurate stack pointer to exit the function,
insert some code to save and restore the stack pointer. */
--- gcc/testsuite/gcc.dg/pr87485.c.jj 2019-02-01 16:30:51.101211900 +0100
+++ gcc/testsuite/gcc.dg/pr87485.c 2019-02-01 16:31:48.660260183 +0100
@@ -0,0 +1,29 @@
+/* PR rtl-optimization/87485 */
+/* { dg-do compile { target int128 } } */
+/* { dg-options "-O2 -fschedule-insns -fno-guess-branch-probability
-fno-isolate-erroneous-paths-dereference -fno-omit-frame-pointer
-fno-split-wide-types -fno-tree-ccp -fno-tree-sra" } */
+/* { dg-additional-options "-fstack-protector-strong" { target
fstack_protector } } */
+
+int *a;
+
+int
+foo (__int128 x, int y, int z)
+{
+ __int128 b;
+ *a = ((!!y ? y : x) * y | x) * 2;
+ if (z == 0)
+ {
+ unsigned int c = 1;
+ __int128 *d = &b;
+ for (*a = 0; *a < 1; *a += y)
+ ;
+ *a += b < (c / 0); /* { dg-warning "division by zero" } */
+ goto l;
+ m:
+ while (b < 1)
+ ;
+ ++*a;
+ }
+ goto m;
+ l:
+ return 0;
+}
Jakub
