Re: [Xen-devel] [PATCH v2 for-4.9 2/2] x86/emul: Reorder the user segments in x86_segment to match SReg3 encoding

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 26/10/16 09:57, Jan Beulich wrote:
>>>> On 25.10.16 at 20:10, <andrew.cooper3@xxxxxxxxxx> wrote:
>> @@ -2994,8 +2978,8 @@ x86_emulate(
>>          break;
>>  
>>      case 0x8e: /* mov r/m,Sreg */
>> -        seg = decode_segment(modrm_reg);
>> -        generate_exception_if(seg == decode_segment_failed, EXC_UD, -1);
>> +        seg = modrm_reg & 7; /* REX.R is ignored. */
>> +        generate_exception_if(!is_x86_user_segment(seg), EXC_UD, -1);
>>          generate_exception_if(seg == x86_seg_cs, EXC_UD, -1);
> Can I talk you into folding these two generate_exception_if()s, as
> they logically belong together?

Ok.

>
>> @@ -5438,6 +5422,17 @@ x86_emulate(
>>  #undef override_seg
>>  #undef ea
>>  
>> +static void __init __maybe_unused build_assertions(void)
>> +{
>> +    /* Check the values against SReg3 encoding in opcode/ModRM bytes. */
>> +    BUILD_BUG_ON(x86_seg_es != 0);
>> +    BUILD_BUG_ON(x86_seg_cs != 1);
>> +    BUILD_BUG_ON(x86_seg_ss != 2);
>> +    BUILD_BUG_ON(x86_seg_ds != 3);
>> +    BUILD_BUG_ON(x86_seg_fs != 4);
>> +    BUILD_BUG_ON(x86_seg_gs != 5);
>> +}
> So using an inline function in the header did not work out?

No - that would involve making BUILD_BUG_ON() available to x86_emulate.h

In this position, it does also affect the test harness build, as it is
outside an #ifdef __XEN__ block.

>
> In any event,
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

Thanks

~Andrew

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