Re: [PATCH 1/2] target/s390x: Define TARGET_HAS_PRECISE_SMC

[David Hildenbrand <david@redhat.com>]

On 07.08.23 18:13, Ilya Leoshkevich wrote:
> On Mon, 2023-08-07 at 17:31 +0200, David Hildenbrand wrote:
>> On 07.08.23 13:48, Ilya Leoshkevich wrote:
>>> PoP (Sequence of Storage References -> Instruction Fetching) says:
>>>
>>>       ... if a store that is conceptually earlier is
>>>       made by the same CPU using the same effective
>>>       address as that by which the instruction is subse-
>>>       quently fetched, the updated information is obtained ...
>>>
>>> QEMU already has support for this in the common code; enable it for
>>> s390x.
>>
>>
>> Figuring out what TARGET_HAS_PRECISE_SMC is all about, I only learned
>> from git history
>>
>> commit d720b93d0bcfe1beb729245b9ed1e5f071a24bd5
>> Author: Fabrice Bellard <fabrice@bellard.org>
>> Date:   Sun Apr 25 17:57:43 2004 +0000
>>
>>       precise self modifying code support
>>
>>
>>       git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@745
>> c046a42c-6fe2-441c-8c8c-71466251a162
>>
>>
>>
>> AFAIU, precise SMC is stricter compared to what we have right now. So
>> i
>> suspect that this patch is actually fixing SMC behavior: for example,
>> when a basic block ends up modifying itself.
>>
>> Were there any BUG reports? (does patch #2 test for that and can
>> reproduce the original issue?)
> 
> There were no bug reports, I found this issue with fuzzing.
> 
> Patch #2 tests a TB modifying itself.
> Reverting this commit makes the test fail.
> 
> [...]
> 

Cool, thanks. Worth adding to the patch description.

Acked-by: David Hildenbrand <david@redhat.com>

-- 
Cheers,

David / dhildenb