[all-commits] [llvm/llvm-project] 3d3405: [X86, MC] Add relocation R_X86_64_REX2_GOTPCRELX (#...

[Shengchen Kan via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 3d34053af61ff45e05d230d2678eb8e95322eb14
      https://github.com/llvm/llvm-project/commit/3d34053af61ff45e05d230d2678eb8e95322eb14
  Author: Shengchen Kan <shengchen.kan at intel.com>
  Date:   2024-09-24 (Tue, 24 Sep 2024)

  Changed paths:
    M clang/test/Driver/relax.s
    M llvm/include/llvm/BinaryFormat/ELFRelocs/x86_64.def
    M llvm/lib/MC/MCTargetOptionsCommandFlags.cpp
    M llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp
    M llvm/lib/Target/X86/MCTargetDesc/X86ELFObjectWriter.cpp
    M llvm/lib/Target/X86/MCTargetDesc/X86FixupKinds.h
    M llvm/lib/Target/X86/MCTargetDesc/X86MCCodeEmitter.cpp
    M llvm/lib/Target/X86/MCTargetDesc/X86MachObjectWriter.cpp
    M llvm/lib/Target/X86/MCTargetDesc/X86WinCOFFObjectWriter.cpp
    M llvm/test/MC/ELF/relocation-alias.s
    M llvm/test/MC/X86/gotpcrelx.s
    M llvm/test/MC/X86/reloc-directive-elf-64.s

  Log Message:
  -----------
  [X86,MC] Add relocation R_X86_64_REX2_GOTPCRELX (#106681)

For

	mov        name at GOTPCREL(%rip), %reg
	test       %reg, name at GOTPCREL(%rip)
	binop      name at GOTPCREL(%rip), %reg

where binop is one of adc, add, and, cmp, or, sbb, sub, xor
instructions, add

 `R_X86_64_REX2_GOTPCRELX`/`R_X86_64_CODE_4_GOTPCRELX` = 43

if the instruction starts at 4 bytes before the relocation offset. It
similar to R_X86_64_GOTPCRELX.

Linker can treat `R_X86_64_REX2_GOTPCRELX`/`R_X86_64_CODE_4_GOTPCRELX`
as `R_X86_64_GOTPCREL` or convert the above instructions to

	lea	name(%rip), %reg
	mov	$name, %reg
	test	$name, %reg
	binop	$name, %reg

if the first byte of the instruction at the relocation `offset - 4` is
`0xd5` (namely, encoded w/ REX2 prefix) when possible.

Binutils patch:
https://github.com/bminor/binutils-gdb/commit/3d5a60de52556f6a53d71d7e607c6696450ae3e4
Binutils mailthread:
https://sourceware.org/pipermail/binutils/2023-December/131462.html
ABI discussion: https://groups.google.com/g/x86-64-abi/c/KbzaNHRB6QU
Blog: https://kanrobert.github.io/rfc/All-about-APX-relocation



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