Re: [Xen-devel] [PATCH v5 01/47] x86emul: introduce IMPOSSIBLE()

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 19.11.18 at 19:11, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 19/11/2018 10:13, Jan Beulich wrote:
>> @@ -8828,12 +8837,7 @@ x86_emulate(
>>                  dst.type = OP_NONE;
>>                  break;
>>              default:
>> -                if ( (d & DstMask) != DstMem )
>> -                {
>> -                    ASSERT_UNREACHABLE();
>> -                    rc = X86EMUL_UNHANDLEABLE;
>> -                    goto done;
>> -                }
>> +                IMPOSSIBLE((d & DstMask) != DstMem);
> 
> IMPOSSIBLE() doesn't really convey the correct meaning here IMO, because
> the purpose of the construct is to try and do something safe in the case
> that the impossible does happen.
> 
> Instead, I'd suggest EXPECT() or REQUIRE() with an inverted condition,
> because that better encapsulates the meaning that we expect this always
> to be true, but that it might not be.

Okay, EXPECT() it'll be then.

> With a suitable name, Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Thanks.

Jan



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