[PATCH] x86: Update register operand check for AddrPrefixOpReg

[H.J. Lu]

On Thu, Oct 1, 2020 at 7:57 AM Jan Beulich <jbeulich@suse.com> wrote:
>
> 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.
>

GNU assembler accommodates other usages.  But it must work with GCC.
In this case, it needs to check the register operand for the address size prefix
when the memory operand is (%rip).

-- 
H.J.