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Re: [Qemu-devel] [PATCH] Fix missing TRACE exception
From: |
Andreas Färber |
Subject: |
Re: [Qemu-devel] [PATCH] Fix missing TRACE exception |
Date: |
Fri, 23 Nov 2012 17:35:38 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:16.0) Gecko/20121025 Thunderbird/16.0.2 |
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
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