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Re: [PATCH RFC] x86: SYSENTER/SYSEXIT are unavailable in 64-bit mode on AMD
On 12.11.2019 21:26, H.J. Lu wrote:
> On Mon, Nov 11, 2019 at 11:13 PM Jan Beulich <jbeulich@suse.com> wrote:
>>
>> On 11.11.2019 18:12, H.J. Lu wrote:
>>> On Mon, Nov 11, 2019 at 4:01 AM Jan Beulich <jbeulich@suse.com> wrote:
>>>> RFC because this is liable to cause problems for existing code, but I
>>>> think we should still correct this. We may want to have a directive
>>>> (besides the command line option) such that the accepted ISA can be
>>>> overridden in a more fine granular manner.
>>>
>>> I think it is an overkill.
>>
>> Well, even better if this means you're fine with the patch as is
>> (seeing that below you're even suggesting a more rigid approach).
>>
>>>> --- a/opcodes/i386-opc.tbl
>>>> +++ b/opcodes/i386-opc.tbl
>>>> @@ -891,8 +891,10 @@ rdmsr, 0, 0xf32, None, 2, Cpu586, No_bSu
>>>> cmpxchg8b, 1, 0xfc7, 0x1, 2, Cpu586, Modrm|No_bSuf|No_wSuf|No_lSuf|No_sSuf|No_ldSuf|IsLockable|NoRex64|HLEPrefixOk, { Qword|Unspecified|BaseIndex }
>>>>
>>>> // Pentium II/Pentium Pro extensions.
>>>> -sysenter, 0, 0xf34, None, 2, Cpu686, No_bSuf|No_wSuf|No_lSuf|No_sSuf|No_qSuf|No_ldSuf, { 0 }
>>>> -sysexit, 0, 0xf35, None, 2, Cpu686, No_bSuf|No_wSuf|No_lSuf|No_sSuf|No_qSuf|No_ldSuf, { 0 }
>>>> +sysenter, 0, 0xf34, None, 2, Cpu686, Intel64|No_bSuf|No_wSuf|No_lSuf|No_sSuf|No_qSuf|No_ldSuf, { 0 }
>>>> +sysenter, 0, 0xf34, None, 2, Cpu686|CpuNo64, AMD64|No_bSuf|No_wSuf|No_lSuf|No_sSuf|No_qSuf|No_ldSuf, { 0 }
>>>> +sysexit, 0, 0xf35, None, 2, Cpu686, Intel64|No_bSuf|No_wSuf|No_lSuf|No_sSuf|No_qSuf|No_ldSuf, { 0 }
>>>> +sysexit, 0, 0xf35, None, 2, Cpu686|CpuNo64, AMD64|No_bSuf|No_wSuf|No_lSuf|No_sSuf|No_qSuf|No_ldSuf, { 0 }
>>>> fxsave, 1, 0xfae, 0x0, 2, CpuFXSR, Modrm|No_bSuf|No_wSuf|No_lSuf|No_sSuf|No_ldSuf, { Unspecified|BaseIndex }
>>>> fxsave64, 1, 0xfae, 0x0, 2, CpuFXSR|Cpu64, Modrm|No_bSuf|No_wSuf|No_lSuf|No_sSuf|No_qSuf|No_ldSuf|Rex64, { Unspecified|BaseIndex }
>>>> fxrstor, 1, 0xfae, 0x1, 2, CpuFXSR, Modrm|No_bSuf|No_wSuf|No_lSuf|No_sSuf|No_ldSuf, { Unspecified|BaseIndex }
>>>
>>> Are there any usages in 64-bit mode? If not, just disallow them in 64-bit mode.
>>
>> Usages - I don't know. But I do know that they're usable.
>
> They can use REX.W prefix if needed.
How does use (or not) of REX.W relate to whether or not to allow the insns
in 64-bit mode? There's nothing to add REX.W to if the insns wouldn't be
accepted by gas. (As an aside, I don't think REX.W matters for these insns
in any way.)
Jan