[PATCH] x86-64: Relax BFD_RELOC_X86_64_GOTTPOFF check

[H.J. Lu]

On Thu, Jun 27, 2024, 5:25 PM Jan Beulich <jbeulich@suse.com> wrote:

> On 27.06.2024 08:06, Kong, Lingling wrote:
> >> --- a/gas/config/tc-i386.c
> >> +++ b/gas/config/tc-i386.c
> >> @@ -7137,7 +7137,8 @@ md_assemble (char *line)
> >>              && i.base_reg
> >>              && i.base_reg->reg_num == RegIP
> >>              && i.tm.operand_types[0].bitfield.class == Reg
> >> -            && i.tm.operand_types[2].bitfield.class == Reg)
> >> +            && (i.tm.operand_types[2].bitfield.class == Reg
> >> +                || (i.tm.operands == 2 && i.tm.opcode_modifier.nf)))
> >>            /* Allow APX: add %reg1, foo@gottpoff(%rip), %reg2.  */
> >>            break;
>
> What does the i.tm.opcode_modifier.nf check achieve here? All EVexMap4
> ADD forms permit {nf}. The comment also needs updating, to avoid it
> going further stale (it already hasn't been quite accurate). With the
> comment properly updated to list all permissible forms, I think you'll
> also note that what you add to the condition is too lax: Aiui
>
>         add %rax, foo@GOTTPOFF(%rip)
>
> is not supposed to be permitted (according to the testsuite additions
> you make).
>
> Finally a question perhaps more for H.J. than for you: Why is it that
> ADD is special-cased here for the APX EVEX-encoded case, when there's
> no similar special casing for legacy encodings?
>

ADD is the part of TLS sequence.


> >> --- a/gas/testsuite/gas/i386/x86-64-gottpoff.s
> >> +++ b/gas/testsuite/gas/i386/x86-64-gottpoff.s
> >> @@ -18,8 +18,22 @@ _start:
> >>
> >>      addq    %r8, foo@GOTTPOFF(%rip), %r16
> >>      addq    foo@GOTTPOFF(%rip), %rax, %r12
> >> +    {nf} addq       %r8, foo@GOTTPOFF(%rip), %r16
> >> +    {nf} addq       foo@GOTTPOFF(%rip), %rax, %r12
> >>
> >>      .intel_syntax noprefix
> >>
> >>      add     r16, QWORD PTR [rip + foo@GOTTPOFF], r8
> >>      add     r12, rax, QWORD PTR [rip + foo@GOTTPOFF]
> >> +    {nf} addq       r16, QWORD PTR [rip + foo@GOTTPOFF], r8
> >> +    {nf} addq       r12, rax, QWORD PTR [rip + foo@GOTTPOFF]
> >
> >  +    {nf} add                r16, QWORD PTR [rip + foo@GOTTPOFF], r8
> >  +    {nf} add        r12, rax, QWORD PTR [rip + foo@GOTTPOFF]
> >
> >> +
> >> +    .att_syntax prefix
> >> +
> >> +    {nf} addq       foo@GOTTPOFF(%rip), %rax
> >> +    {nf} addq       foo@GOTTPOFF(%rip), %r16
>
> Isn't the {evex} form similarly permitted by the change you make to
> tc-i386.c?
>
> Jan
>
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