Re: [PATCH] [gdb/testsuite] Fix gdb.arch/i386-avx.exp with clang

Andrew Burgess via Gdb-patches
2021-11-05T09:33:31Z

* Tom de Vries via Gdb-patches <gdb-patches@sourceware.org> [2021-11-04 14:55:59 +0100]:

> When running test-case gdb.arch/i386-avx.exp with clang I ran into:
> ...
> (gdb) PASS: gdb.arch/i386-avx.exp: set first breakpoint in main
> continue^M
> Continuing.^M
> ^M
> Program received signal SIGSEGV, Segmentation fault.^M
> 0x000000000040052b in main (argc=1, argv=0x7fffffffd3c8) at i386-avx.c:54^M
> 54 asm ("vmovaps 0(%0), %%ymm0\n\t"^M
> (gdb) FAIL: gdb.arch/i386-avx.exp: continue to breakpoint: \
> continue to first breakpoint in main
> ...
>
> The problem is that the vmovaps insn requires an 256-bit (or 32-byte aligned
> address), and it's only 16-byte aligned:
> ...
> (gdb) p /x $rax
> $1 = 0x601030
> ...
>
> Fix this by copying to a sufficiently aligned address.
>
> Tested on x86_64-linux, with both gcc and clang.
> ---
> gdb/testsuite/gdb.arch/i386-avx.c | 28 +++++++++++++++++++++++++++-
> 1 file changed, 27 insertions(+), 1 deletion(-)
>
> diff --git a/gdb/testsuite/gdb.arch/i386-avx.c b/gdb/testsuite/gdb.arch/i386-avx.c
> index 4e938399a24..9b5323f9f76 100644
> --- a/gdb/testsuite/gdb.arch/i386-avx.c
> +++ b/gdb/testsuite/gdb.arch/i386-avx.c
> @@ -18,6 +18,9 @@
> along with this program. If not, see <http://www.gnu.org/licenses/>. */
>
> #include <stdio.h>
> +#include <stdint.h>
> +#include <assert.h>
> +#include <string.h>
> #include "nat/x86-cpuid.h"
>
> typedef struct {
> @@ -25,7 +28,7 @@ typedef struct {
> } v8sf_t;
>
>
> -v8sf_t data[] =
> +v8sf_t data_orig[] =

I see the same problem. Did you consider using:

/* Some useful comment .... */
v8sf_t data[] __attribute__ ((aligned(32))) = ....

this seems to fix the problem on clang for me, and still works fine
with gcc.

Thanks,
Andrew

> {
> { { 0.0, 0.125, 0.25, 0.375, 0.50, 0.625, 0.75, 0.875 } },
> { { 1.0, 1.125, 1.25, 1.375, 1.50, 1.625, 1.75, 1.875 } },
> @@ -47,10 +50,33 @@ v8sf_t data[] =
> #endif
> };
>
> +float data_buf[sizeof (data_orig) * 2 / sizeof (float)];
>
> int
> main (int argc, char **argv)
> {
> + v8sf_t *data;
> +
> + /* Initialize data pointer. */
> + {
> + float *p = data_buf;
> + float *data_buf_end = &data_buf[sizeof (data_buf) / sizeof (*data_buf)];
> + while (((uintptr_t)p & 0x1f) != 0
> + && p < data_buf_end)
> + p++;
> + data = (v8sf_t *)p;
> + }
> +
> + /* Check that data pointer is sufficiently aligned to use vmovaps. */
> + assert (((uintptr_t)data & 0x1f) == 0);
> +
> + /* Check that memcpy does not write out of bounds. */
> + assert ((void *)data + sizeof (data_orig)
> + <= (void *)data_buf + sizeof (data_buf));
> +
> + /* Initialize data contents. */
> + memcpy (data, data_orig, sizeof (data_orig));
> +
> asm ("vmovaps 0(%0), %%ymm0\n\t"
> "vmovaps 32(%0), %%ymm1\n\t"
> "vmovaps 64(%0), %%ymm2\n\t"
>
> base-commit: edc77c591add0a9c7740a9ed9f7e40358bf65dbf
> --
> 2.26.2
>