Re: [Qemu-devel] [PATCH] Fix missing TRACE exception

[Andreas Färber]

Am 23.11.2012 17:06, schrieb Alexander Graf:
> 
> On 19.10.2012, at 12:17, Julio Guerra wrote:
> 
>> This patch fixes bug 1031698 :
>> https://bugs.launchpad.net/qemu/+bug/1031698
>>
>> If we look at the (truncated) translation of the conditional branch
>> instruction in the test submitted in the bug post, the call to the
>> exception helper is missing in the "bne-false" chunk of translated
>> code :
>>
>> IN:
>> bne-    0x1800278
>>
>> OUT:
>> 0xb544236d:  jne    0xb5442396
>>
>> 0xb5442373:  mov    %ebp,(%esp)
>> 0xb5442376:  mov    $0x44,%ebx
>> 0xb544237b:  mov    %ebx,0x4(%esp)
>> 0xb544237f:  mov    $0x1800278,%ebx
>> 0xb5442384:  mov    %ebx,0x25c(%ebp)
>> 0xb544238a:  call   0x827475a
>>                     ^^^^^^^^^^^^^^^^^^
>> # OK : call the exception helper function
>>
>> 0xb5442396:  mov    %ebp,(%esp)
>> 0xb5442399:  mov    $0x44,%ebx
>> 0xb544239e:  mov    %ebx,0x4(%esp)
>> 0xb54423a2:  mov    $0x1800270,%ebx
>> 0xb54423a7:  mov    %ebx,0x25c(%ebp)
>> # KO : missing "call 0x827475a"
>>
>>
>> Indeed, gen_exception(ctx, excp) called by gen_goto_tb (called by
>> gen_bcond) changes ctx->exception's value to excp's :
>>
>> gen_bcond()
>> {
>>  gen_goto_tb(ctx, 0, ctx->nip + li - 4);
>>  /* ctx->exception value is POWERPC_EXCP_BRANCH */
>>
>>  gen_goto_tb(ctx, 1, ctx->nip);
>>  /* ctx->exception now value is POWERPC_EXCP_TRACE */
>> }
>>
>>
>> Making the following gen_goto_tb()'s test false during the second call :
>>
>> if ((ctx->singlestep_enabled &
>>    (CPU_BRANCH_STEP | CPU_SINGLE_STEP)) &&
>>    ctx->exception == POWERPC_EXCP_BRANCH /* false...*/) {
>>         target_ulong tmp = ctx->nip;
>>         ctx->nip = dest;
>>         /* ... and this is the missing call */
>>         gen_exception(ctx, POWERPC_EXCP_TRACE);
>>         ctx->nip = tmp;
>> }
>>
>> So the patch simply adds the missing matching case, fixing our problem.
>>
>> Signed-off-by: Julio Guerra <address@hidden>
> 
> Thanks, applied to ppc-next :)

Please don't forget to add the missing "target-ppc: ". :)

Andreas

-- 
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg, Germany
GF: Jeff Hawn, Jennifer Guild, Felix Imendörffer; HRB 16746 AG Nürnberg