[PATCH] x86: Add x86_is_elf to optimize out the ELF check

[H.J. Lu]

On Tue, Sep 24, 2024 at 5:57 PM Jan Beulich <jbeulich@suse.com> wrote:
>
> On 24.09.2024 11:10, H.J. Lu wrote:
> >  On Tue, Sep 24, 2024 at 4:19 PM Jan Beulich <jbeulich@suse.com> wrote:
> >>
> >> On 24.09.2024 00:56, H.J. Lu wrote:
> >>> Add x86_is_elf and replace IS_ELF with x86_is_elf () so that compiler
> >>> can optimize out the ELF check when OBJ_ELF is defined and OBJ_MAYBE_ELF
> >>> isn't defined.
> >>>
> >>> * config/tc-i386.c (x86_is_elf): New function.
> >>> (check_cpu_arch_compatible): Replace IS_ELF with x86_is_elf ().
> >>> (i386_arch): Likewise.
> >>> (i386_mach): Likewise.
> >>> (tc_i386_fix_adjustable): Likewise.
> >>> (i386_assemble): Likewise.
> >>> (need_plt32_p): Likewise.
> >>> (x86_cleanup): Likewise.
> >>> (output_insn): Likewise.
> >>> (lex_got): Likewise.
> >>> (s_insn): Likewise.
> >>> (md_estimate_size_before_relax): Likewise.
> >>> (md_apply_fix): Likewise.
> >>> (md_parse_option): Likewise.
> >>> (i386_target_format): Likewise.
> >>> (i386_validate_fix): Likewise.
> >>> (tc_gen_reloc): Likewise.
> >>>
> >>
> >> Sadly there's no actual patch, so I can only guess what it does. I think
> >> we don't need this anymore, with the plan to do away with OBJ_MAYBE_ELF
> >
> > OBJ_MAYBE_ELF is used by the configure option like,
> >
> > --enable-targets=x86_64-mingw64
> >
> > I don't think we should remove it unless there is a very good reason.
>
> You give precisely an example of why we should remove it: That target
> wants PE/COFF support, but what it gets as emulation is plain COFF.
> That's wrong. I was actually half way through addressing this aspect,
> when it occurred to me that the issue is far worse. While even COFF
> has more than 2 sub-flavors (go32 for example), ELF has yet more
> (GNU, Solaris, FreeBSD, Lynx, NetBSD, VxWorks, and maybe more). If we
> wanted to get things right, all TE_* checks anywhere (including ones
> which are presently missing anyway) would need to become runtime
> checks, and we'd need an emulation for each flavor. That's simply
> going to be unwieldy. Hence Nick and I agreed that we'd drop
> emulation support for i386 instead. (Note also that there's been no
> testing of those emulations in the x86 gas testsuite, which may be
> part of why no issues were ever noticed with the wrong COFF emulation
> being chosen when enabling a PE/COFF target as secondary one.)
>

When will OBJ_MAYBE_ELF be removed?  If it won't happen soon,
I'd like to check my patch.

Thanks.

-- 
H.J.