Re: [Xen-devel] [PATCH 02/17] x86emul: fetch all insn bytes during the decode phase

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 13.09.16 at 20:44, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 08/09/16 14:07, Jan Beulich wrote:
>> @@ -1602,6 +1602,45 @@ struct x86_emulate_state {
>>  #define _regs (state->regs)
>>  
>>  static int
>> +x86_decode_base(
> 
> What do you mean by decode_base here?

The base instruction set (no 0f or alike prefixes). Suggestions for
a better name welcome.

>> @@ -2644,18 +2704,13 @@ x86_emulate(
>>  
>>      case 0x9a: /* call (far, absolute) */ {
>>          struct segment_register reg;
>> -        uint16_t sel;
>> -        uint32_t eip;
>>  
>> -        generate_exception_if(mode_64bit(), EXC_UD, -1);
>> +        ASSERT(!mode_64bit());
> 
> Are we going to strictly require that noone ever hand-crafts a
> x86_emulate_state and hands it to x86_emulate()?

Absolutely - that's why its definition does not live in a header.

> I would suggest leaving the generate_exception_if(mode_64bit(), EXC_UD,
> -1); after the ASSERT() so even if we do end up in a wonky state, we
> don't try to jump the guest to 0.

That would look really strange to a reader, I think, and hence I'd
rather not do this if I can get the patch accepted without.

Jan


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