For
mov name@GOTPCREL(%rip), %reg
test %reg, name@GOTPCREL(%rip)
binop name@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:
3d5a60de52
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
3d34053af6