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

[Tom de Vries <tdevries@suse.de>]

On 11/5/21 10:33 AM, Andrew Burgess wrote:
> * 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.

I did consider this, and decided against it because it's not portable.

Note btw that there is no other usage of this:
...
$ find gdb/testsuite/ -type f | xargs grep attribute.*align
$
...

Btw, I now realize that gdb.arch/i386-sse.exp has the same issue, I'll
try to factor out a solution that can used in both test-cases.

Thanks,
- Tom