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

[Andrew Burgess <aburgess@redhat.com>]

* 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
>