Re: [Xen-devel] [PATCH v2 12/13] fuzz/x86_emulate: Set and fuzz more CPU state

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 05.10.17 at 19:08, <george.dunlap@xxxxxxxxxx> wrote:
> On 10/04/2017 09:28 AM, Jan Beulich wrote:
>>>>> On 25.09.17 at 16:26, <george.dunlap@xxxxxxxxxx> wrote:
>>> @@ -597,6 +599,47 @@ static const struct x86_emulate_ops all_fuzzer_ops = {
>>>  };
>>>  #undef SET
>>>  
>>> +static void _set_fpu_state(char *fxsave, bool store)
>>> +{
>>> +    if ( cpu_has_fxsr )
>>> +    {
>>> +        static union __attribute__((__aligned__(16))) {
>>> +            char x[464];
>> 
>> The final part of the save area isn't being written, yes, but is it
>> really worth saving the few bytes of stack space here, rather than
>> having the expected 512 as array dimension?
> 
> So I didn't actually look into this very much; I mainly just hacked at
> it until it seemed to work.  I copied-and-pasted emul_test_init() from
> x86_emulate.c (which is where the 464 came from), then copied some
> scraps of asm from stackoverflow.

One thing that came to mind in this context: It would perhaps be
useful to not waste input bytes on the unused portions of the
save area. Along those lines it may also be worth considering not
to waste input on the high halves of 64-bit registers as well as
the high 8 GPRs when emulating 32- or 16-bit mode.

Jan


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