[PATCH] x86: Update register operand check for AddrPrefixOpReg

[Jan Beulich]

On 01.10.2020 15:44, H.J. Lu wrote:
> On Thu, Oct 1, 2020 at 6:23 AM Jan Beulich <jbeulich@suse.com> wrote:
>>
>> On 01.10.2020 15:07, H.J. Lu wrote:
>>> On Thu, Oct 1, 2020 at 4:35 AM H.J. Lu <hjl.tools@gmail.com> wrote:
>>>>
>>>> On Thu, Oct 1, 2020 at 1:22 AM Jan Beulich <jbeulich@suse.com> wrote:
>>>>>
>>>>> On 01.10.2020 01:30, H.J. Lu via Binutils wrote:
>>>>>> I am checking in this patch and backporting it to 2.35 branch.
>>>>>
>>>>> But this is wrong, as can be seen from e.g. ...
>>>>>> + +[a-f0-9]+: 66 0f 38 f8 0d 00 00 00 00      movdir64b 0x0\(%rip\),%rcx        #.*
>>>>>> + +[a-f0-9]+: 67 66 0f 38 f8 0d 00 00 00 00   movdir64b 0x0\(%eip\),%ecx        #.*
>>>>>> + +[a-f0-9]+: 67 66 0f 38 f8 0d 00 00 00 00   movdir64b 0x0\(%eip\),%ecx        #.*
>>>>>
>>>>> ... the middle line here not matching up with
>>>>>
>>>>>> +     movdir64b foo(%rip),%rcx
>>>>>> +     movdir64b foo(%rip),%ecx
>>>>>> +     movdir64b foo(%eip),%ecx
>>>>>
>>>>> ... what was written here. Without your change this
>>>>>
>>>>>         movdir64b (%rbp), %rax
>>>>>         movdir64b (%rbp), %eax
>>>>>         movdir64b (%ebp), %rax
>>>>>         movdir64b (%ebp), %eax
>>>>>
>>>>>         movdir64b (%rip), %rax
>>>>>         movdir64b (%rip), %eax
>>>>>         movdir64b (%eip), %rax
>>>>>         movdir64b (%eip), %eax
>>>>>
>>>>> yields consistent results for both blocks - the middle two entries
>>>>> get an error issued.
>>>>>
>>>>> Please revert, and once again please don't commit (let alone
>>>>> backport) patches without giving people at least _a little bit_ of
>>>>> time to look at them.
>>>>>
>>>>
>>>> The fix is correct.   This specific case came from
>>>>
>>>> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97257
>>>>
>>>> The address prefix changes the register operand in these instructions.
>>>> (%rip) is a special case.
>>>>
>>>
>>> Update the fix for DISP and SYMBOL.
>>
>> The description wrongly says:
>>
>> "When the address size prefix applies to both the memory and the register
>>  operand, we need to extract the address size prefix from the register
>>  operand if the memory operand has no real registers, like symbol, DISP
>>  or symbol(%rip)."
>>
>> And then similarly a code comment. To the assembler, %rip _is_ a real
>> register (and %eip could be used in its stead, when 32-bit addressing is
>> desired).
> 
> GNU assembler serves GCC.  GCC doesn't use (%eip) and GCC always
> uses (%rip) for RIP-relative addressing.

This may be its main purpose, but it's by far not its only one.

Jan