Re: [Qemu-devel] [PATCH 0/4] target-i386: Don't try to enable unsupported TCG features by default

[Paolo Bonzini]

On 14/09/2015 19:31, Richard Henderson wrote:
> On 09/14/2015 10:23 AM, Paolo Bonzini wrote:
>>
>>
>> On 14/09/2015 19:21, Richard Henderson wrote:
>>>>> About implementing DE in TCG: I really don't think it is easier, but if
>>>>>>> somebody wants to implement it, it would be welcome.
>>>>>
>>>>> Actually I agree that it's easier, and even a partial implementation
>>>>> (e.g. no I/O port breakpoints) would be nice to have because recent
>>>>> Windows IIRC requires DE.
>>> Isn't I/O port breakpoints the only thing we're missing from DE?
>>
>> I was thinking of the CR4 bit, but it looks like we don't raise #GP at
>> all on writes to unknown CR0 or CR4 bits.
> 
> Nor do we #gp accesses to dr[45] with DE, nor map dr[45] to dr[67] without DE.
> 
> Does the i/o breakpoint happen before or after the access?  If before, we 
> could
> implement the breakpoint in check_io.  Otherwise we'd need a new helper.

Table 6-3 says it's a trap, so it occurs after.

Paolo