[PATCH v3] x86: Generate PLT32 relocation for ".long foo@PLT - .L4"

[H.J. Lu]

On Mon, Jul 27, 2026 at 3:58 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Mon, Jul 27, 2026 at 3:46 PM Jan Beulich <jbeulich@suse.com> wrote:
> >
> > On 27.07.2026 05:47, H.J. Lu wrote:
> > > On Sat, Jul 25, 2026 at 10:35 AM H.J. Lu <hjl.tools@gmail.com> wrote:
> > >>
> > >> Add BFD_RELOC_X86_64_PLT32 and use it to generate R_X86_64_PLT32 for
> > >> directives like ".long foo@PLT - .L4" so that PLT entries are used to
> > >> resolve the PC32 relocation against function symbols for such directives.
> > >>
> > >> bfd/
> > >>
> > >> PR gas/34423
> > >> * elf64-x86-64.c (x86_64_reloc_map): Add BFD_RELOC_X86_64_PLT32.
> > >> * reloc.c (bfd_reloc_code_real): Add BFD_RELOC_X86_64_PLT32.
> > >> * bfd-in2.h: Regenerated.
> > >> * libbfd.h: Likewise.
> > >>
> > >> gas/
> > >>
> > >> PR gas/34423
> > >> * config/tc-i386.c (x86_cons): Return BFD_RELOC_X86_64_PLT32 for
> > >> directives like ".long foo@PLT - .L4".
> > >> (tc_gen_reloc): Generate R_X86_64_PLT32 for BFD_RELOC_X86_64_PLT32
> > >> with addend computed like R_X86_64_PC32.
> > >> * testsuite/gas/i386/reloc64.l: Updated.
> > >> * testsuite/gas/i386/reloc64.s: Replace ".long xtrn@plt - ." with
> > >> ".long xtrn@plt - _start".
> > >> * testsuite/gas/i386/ilp32/reloc64.l: Updated.
> > >> * testsuite/gas/i386/ilp32/reloc64.s: Replace ".long xtrn@plt - ."
> > >> with ".long xtrn@plt - ptr".
> > >> * testsuite/gas/i386/x86-64-jump-table.d: New file.
> > >> * testsuite/gas/i386/x86-64-jump-table.d: Likewise.
> > >> * testsuite/gas/i386/x86-64-jump-table.s: Likewise.
> > >> * testsuite/gas/i386/x86-64.exp: Run x86-64-jump-table.
> > >> * testsuite/gas/i386/ilp32/x86-64-jump-table.d: New file.
> > >>
> > >> ld/
> > >>
> > >> PR gas/34423
> > >> * testsuite/ld-x86-64/pr34423.c: New file.
> > >> * testsuite/ld-x86-64/x86-64-jump-table.s: Likewise.
> > >> * testsuite/ld-x86-64/x86-64.exp: Run gas/34423 tests.
> > >
> > > Add i386 support like LLVM assembler in the v2 patch.
> >
> > Why would S_IS_LOCAL() be the criteria? There isn't anything wrong with a
>
> I will remove it.

Removed in v3.

> > global, at the very least a hidden/protected one, is there? Instead don't
> > you want to verify that the subtrahend is in the current section (which
> > of course we may not know until after having parsed all input)?
>
> It will be reverified later :
>
> [hjl@gnu-tgl-3 pic-1]$ cat bar.s
>         .section .rodata
>         .p2align 2
> .L4:
>         .long foo1@PLT - bar
> [hjl@gnu-tgl-3 pic-1]$ ./as  -o bar.o bar.s
> bar.s: Assembler messages:
> bar.s:4: Error: can't resolve foo1 - bar
> [hjl@gnu-tgl-3 pic-1]$
>
> > Surprising code like
> >
> > +      if (fixp->fx_r_type == BFD_RELOC_X86_64_PC32_TO_PLT32)
> > +       code = BFD_RELOC_X86_64_PC32_TO_PLT32;
> > +      else if (fixp->fx_r_type == BFD_RELOC_386_PC32_TO_PLT32)
> > +       code = BFD_RELOC_386_PLT32;
> >
> > imo wants at least a brief comment as to the different behavior for i386
> > vs x86-64.
> >
>
> I will add some comments.

Comments are added in v3.  The difference is explicit addend and implicit
addend.

Here is the v3 patch.

-- 
H.J.
---
LLVM assembler supports directives like ".long foo@PLT - .L4" for i386
and x86-64.  Implement the same feature to generate PLT32 relocation
for directives like ".long foo@PLT - .L4" so that PLT entries are used
to resolve the PC32 relocation against function symbols.

bfd/

PR gas/34423
* elf32-i386.c (elf_i386_reloc_type_lookup): Handle
BFD_RELOC_386_PC32_TO_PLT32.
* elf64-x86-64.c (x86_64_reloc_map): Add
BFD_RELOC_X86_64_PC32_TO_PLT32.
* reloc.c (bfd_reloc_code_real): Add BFD_RELOC_386_PC32_TO_PLT32
and BFD_RELOC_X86_64_PC32_TO_PLT32.
* bfd-in2.h: Regenerated.
* libbfd.h: Likewise.

gas/

PR gas/34423
* config/tc-i386.c (x86_cons): Return
BFD_RELOC_X86_64_PC32_TO_PLT32 or BFD_RELOC_386_PC32_TO_PLT32
for directives like ".long foo@PLT - .L4".
(md_apply_fix): Compute addend for BFD_RELOC_386_PC32_TO_PLT32.
(tc_gen_reloc): Handle BFD_RELOC_X86_64_PC32_TO_PLT32 and
BFD_RELOC_386_PC32_TO_PLT32.  Compute addend like
BFD_RELOC_32_PCREL for BFD_RELOC_X86_64_PC32_TO_PLT32.
* testsuite/gas/i386/i386.exp: Run plt test.
* testsuite/gas/i386/ilp32/reloc64.l: Updated.
* testsuite/gas/i386/ilp32/reloc64.s: Replace ".long xtrn@plt - ."
with ".long xtrn@plt - _start".
* testsuite/gas/i386/ilp32/x86-64-jump-table.d: New file.
* testsuite/gas/i386/plt.d: Likewise.
* testsuite/gas/i386/plt.s: Likewise.
* testsuite/gas/i386/reloc32.l: Updated.
* testsuite/gas/i386/reloc32.s: Replace ".long xtrn@plt - ."
with ".long xtrn@plt - _start".
* testsuite/gas/i386/reloc64.l: Updated.
* testsuite/gas/i386/reloc64.s: Replace ".long xtrn@plt - ." with
".long xtrn@plt - ptr".
* testsuite/gas/i386/x86-64-jump-table.d: New file.
* testsuite/gas/i386/x86-64-jump-table.d: Likewise.
* testsuite/gas/i386/x86-64-jump-table.s: Likewise.
* testsuite/gas/i386/x86-64.exp: Run x86-64-jump-table.

ld/

PR gas/34423
* testsuite/ld-x86-64/pr34423.c: New file.
* testsuite/ld-x86-64/x86-64-jump-table.s: Likewise.
* testsuite/ld-x86-64/x86-64.exp: Run gas/34423 tests.
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