[PATCH V2] sanitizer: [PR110027] Align asan_vec[0] to MAX (BIGGEST_ALIGNMENT / BITS_PER_UNIT, ASAN_RED_ZONE_SIZE)

[liuhongt <hongtao.liu@intel.com>]

> > So, try to add some other variable with larger size and smaller alignment
> > to the frame (and make sure it isn't optimized away).
> >
> > alignb above is the alignment of the first partition's var, if
> > align_frame_offset really needs to depend on the var alignment, it probably
> > should be the maximum alignment of all the vars with alignment
> > alignb * BITS_PER_UNIT <=3D MAX_SUPPORTED_STACK_ALIGNMENT
> >

In asan_emit_stack_protection, when it allocated fake stack, it assume
bottom of stack is also aligned to alignb. And the place violated this
is the first var partition. which is 32 bytes offsets,  it should be
BIGGEST_ALIGNMENT / BITS_PER_UNIT.
So I think we need to use MAX (BIGGEST_ALIGNMENT /
BITS_PER_UNIT, ASAN_RED_ZONE_SIZE) for the first var partition.

Ok?

gcc/ChangeLog:

	PR sanitizer/110027
	* cfgexpand.cc (expand_stack_vars): Align frame offset to
	MAX (BIGGEST_ALIGNMENT / BITS_PER_UNIT, ASAN_RED_ZONE_SIZE).

gcc/testsuite/ChangeLog:

	* g++.dg/asan/pr110027.C: New test.
---
 gcc/cfgexpand.cc                     |  3 ++-
 gcc/testsuite/g++.dg/asan/pr110027.C | 20 ++++++++++++++++++++
 2 files changed, 22 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/g++.dg/asan/pr110027.C

diff --git a/gcc/cfgexpand.cc b/gcc/cfgexpand.cc
index 0de299c62e3..70cc89b29f4 100644
--- a/gcc/cfgexpand.cc
+++ b/gcc/cfgexpand.cc
@@ -1214,7 +1214,8 @@ expand_stack_vars (bool (*pred) (size_t), class stack_vars_data *data)
 	    {
 	      if (data->asan_vec.is_empty ())
 		{
-		  align_frame_offset (ASAN_RED_ZONE_SIZE);
+		  align_frame_offset (MAX (BIGGEST_ALIGNMENT / BITS_PER_UNIT,
+					   ASAN_RED_ZONE_SIZE));
 		  prev_offset = frame_offset.to_constant ();
 		}
 	      prev_offset = align_base (prev_offset,
diff --git a/gcc/testsuite/g++.dg/asan/pr110027.C b/gcc/testsuite/g++.dg/asan/pr110027.C
new file mode 100644
index 00000000000..0067781bc89
--- /dev/null
+++ b/gcc/testsuite/g++.dg/asan/pr110027.C
@@ -0,0 +1,20 @@
+/* PR sanitizer/110027 */
+/* { dg-do run } */
+/* { dg-require-effective-target avx512f_runtime } */
+/* { dg-options "-std=gnu++23 -mavx512f -fsanitize=address -O0 -g -fstack-protector-strong" } */
+
+#include <cstddef>
+#include <cstdint>
+
+template <ptrdiff_t W, typename T>
+using Vec [[gnu::vector_size(W * sizeof(T))]] = T;
+
+auto foo() {
+  Vec<8, int64_t> ret{};
+  return ret;
+}
+
+int main() {
+  foo();
+  return 0;
+}
-- 
2.31.1