Than McIntosh encountered a bug on 32-bit x86 with code that calls
alloca when using -fsplit-stack when -mno-accumulate-outgoing-args is
in effect. When alloca is called after a function call, the arguments
are left on the stack, which can cause the stack to become misaligned.
The problem is simply that the stack-split alloca support is
implemented before calling do_pending_stack_adjust. This patch fixes
the problem and adds a test case. Bootstrapped and ran all tests on
x86_64-pc-linux-gnu. Committed to mainline.
Ian
2016-10-04 Ian Lance Taylor <i...@golang.org>
* explow.c (allocate_dynamic_stack_space): Call
do_pending_stack_adjust before handling flag_split_stack.
2016-10-04 Ian Lance Taylor <i...@golang.org>
* gcc.dg/split-7.c: New test.
Index: gcc/explow.c
===================================================================
--- gcc/explow.c (revision 240755)
+++ gcc/explow.c (working copy)
@@ -1357,6 +1357,8 @@ allocate_dynamic_stack_space (rtx size,
current_function_has_unbounded_dynamic_stack_size = 1;
}
+ do_pending_stack_adjust ();
+
final_label = NULL;
final_target = NULL_RTX;
@@ -1414,8 +1416,6 @@ allocate_dynamic_stack_space (rtx size,
emit_label (available_label);
}
- do_pending_stack_adjust ();
-
/* We ought to be called always on the toplevel and stack ought to be aligned
properly. */
gcc_assert (!(stack_pointer_delta
Index: gcc/testsuite/gcc.dg/split-7.c
===================================================================
--- gcc/testsuite/gcc.dg/split-7.c (revision 0)
+++ gcc/testsuite/gcc.dg/split-7.c (working copy)
@@ -0,0 +1,55 @@
+/* { dg-do run } */
+/* { dg-require-effective-target split_stack } */
+/* { dg-options "-fsplit-stack -O2" } */
+/* { dg-options "-fsplit-stack -O2 -mno-accumulate-outgoing-args" { target { {
i?86-*-* x86_64-*-* } && ia32 } } } */
+
+/* A case that used to fail on 32-bit x86 when optimizing and not
+ using -maccumulate-args. The stack adjustment of the alloca got
+ mixed up with the arguments pushed on the stack to the function
+ before the call of alloca. */
+
+#include <stdlib.h>
+
+typedef struct { const char* s; int l; } s;
+
+typedef unsigned long long align16 __attribute__ ((aligned(16)));
+
+s gobats (const void *, int) __attribute__ ((noinline));
+
+s
+gobats (const void* p __attribute__ ((unused)),
+ int l __attribute__ ((unused)))
+{
+ s v;
+ v.s = 0;
+ v.l = 0;
+ return v;
+}
+
+void check_aligned (void *p) __attribute__ ((noinline));
+
+void
+check_aligned (void *p)
+{
+ if (((__SIZE_TYPE__) p & 0xf) != 0)
+ abort ();
+}
+
+void gap (void *) __attribute__ ((noinline));
+
+void gap (void *p)
+{
+ align16 a;
+ check_aligned (&a);
+}
+
+int
+main (int argc, char **argv)
+{
+ s *space;
+ gobats(0, 16);
+ space = (s *) alloca(sizeof(s) + 1);
+ *space = (s){0, 16};
+ gap(space);
+ return 0;
+}
