On Fri, Nov 14, 2014 at 09:46:14AM +0300, Yury Gribov wrote:
> Hi all,
>
> This patch fixes https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63802 by only
> limiting minimal type alignment with BIGGEST_ALIGNMENT for types with no
> __attribute__((aligned)).
>
> Bootstrapped and regtested on x64. Ok for trunk?
The function is primarily used by the C FE for _Alignas, and I have no idea
if such a change is desirable for that very much user visible case. Joseph?
Alternatively, you can just change ubsan.c caller of min_align_of_type,
use TYPE_USER_ALIGN (type) ? TYPE_ALIGN_UNIT (type) : min_align_of_type (type)
there instead.
> >From 7e5d09453dcff22f591162e1b5c5a115b17b0014 Mon Sep 17 00:00:00 2001
> From: Yury Gribov <y.gri...@samsung.com>
> Date: Thu, 13 Nov 2014 21:29:51 +0300
> Subject: [PATCH] 2014-11-14 Yury Gribov <y.gri...@samsung.com>
>
> PR sanitizer/63802
>
> gcc/
> * stor-layout.c (min_align_of_type): Respect user alignment
> more.
>
> gcc/testsuite/
> * c-c++-common/ubsan/pr63802.c: New test.
> ---
> gcc/stor-layout.c | 2 +-
> gcc/testsuite/c-c++-common/ubsan/pr63802.c | 23 +++++++++++++++++++++++
> 2 files changed, 24 insertions(+), 1 deletion(-)
> create mode 100644 gcc/testsuite/c-c++-common/ubsan/pr63802.c
>
> diff --git a/gcc/stor-layout.c b/gcc/stor-layout.c
> index 431b207..db09855 100644
> --- a/gcc/stor-layout.c
> +++ b/gcc/stor-layout.c
> @@ -2430,9 +2430,9 @@ unsigned int
> min_align_of_type (tree type)
> {
> unsigned int align = TYPE_ALIGN (type);
> - align = MIN (align, BIGGEST_ALIGNMENT);
> if (!TYPE_USER_ALIGN (type))
> {
> + align = MIN (align, BIGGEST_ALIGNMENT);
> #ifdef BIGGEST_FIELD_ALIGNMENT
> align = MIN (align, BIGGEST_FIELD_ALIGNMENT);
> #endif
> diff --git a/gcc/testsuite/c-c++-common/ubsan/pr63802.c
> b/gcc/testsuite/c-c++-common/ubsan/pr63802.c
> new file mode 100644
> index 0000000..454c098
> --- /dev/null
> +++ b/gcc/testsuite/c-c++-common/ubsan/pr63802.c
> @@ -0,0 +1,23 @@
> +/* Limit this to known non-strict alignment targets. */
> +/* { dg-do run { target { i?86-*-linux* x86_64-*-linux* } } } */
> +/* { dg-options "-fsanitize=alignment" } */
> +
> +#define __round_mask(x, y) ((__typeof__(x))((y)-1))
> +#define round_up(x, y) ((((x)-1) | __round_mask(x, y))+1)
> +
> +struct test_struct {
> + unsigned long a;
> + int b;
> +} __attribute__((__aligned__(64)));
> +
> +char a[200];
> +
> +int main ()
> +{
> + volatile int x = ((struct test_struct*)(round_up((unsigned long)a, 64) +
> 16))->b;
> + volatile int y = ((struct test_struct*)(round_up((unsigned long)a, 64) +
> 15))->b;
> +
> + return 0;
> +}
> +
> +/* { dg-output "\.c:18:\[0-9]*: \[^\n\r]*member access within misaligned
> address 0x\[0-9a-fA-F]* for type 'struct test_struct', which requires 64 byte
> alignment.*" } */
> --
> 1.7.9.5
>
Jakub
