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cmd/link/internal/arm64: support Mach-O ARM64_RELOC_SUBTRACTOR in internal linking

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ARM64_RELOC_SUBTRACTOR is the arm64 version of X86_64_RELOC_SUBTRACTOR, which
has been recently implemented in CL 660715.

The standard library still doesn't need it, but I've found it necessary
when statically linking against a library I own.

Change-Id: I138281b12f2304e3673f7dc92f7137e48bf68fdd
Reviewed-on: https://go-review.googlesource.com/c/go/+/703316
Reviewed-by: Carlos Amedee <carlos@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
This commit is contained in:
qmuntal 2025-09-12 16:31:01 +02:00 • committed by Quim Muntal
parent 6e95748335
commit 7c8166d02d
2 changed files with 23 additions and 0 deletions
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22
src/cmd/link/internal/arm64/asm.go
View file

@ -224,6 +224,28 @@ func adddynrel(target *ld.Target, ldr *loader.Loader, syms *ld.ArchSyms, s loade
}
return true
case objabi.MachoRelocOffset + ld.MACHO_ARM64_RELOC_SUBTRACTOR*2:
// ARM64_RELOC_SUBTRACTOR must be followed by ARM64_RELOC_UNSIGNED.
// The pair of relocations resolves to the difference between two
// symbol addresses (each relocation specifies a symbol).
outer, off := ld.FoldSubSymbolOffset(ldr, targ)
if outer != s {
// TODO: support subtracted symbol in different section.
ldr.Errorf(s, "unsupported ARM64_RELOC_SUBTRACTOR reloc: target %s, outer %s", ldr.SymName(targ), ldr.SymName(outer))
break
}
su := ldr.MakeSymbolUpdater(s)
relocs := su.Relocs()
if rIdx+1 >= relocs.Count() || relocs.At(rIdx+1).Type() != objabi.MachoRelocOffset+ld.MACHO_ARM64_RELOC_UNSIGNED*2 || relocs.At(rIdx+1).Off() != r.Off() {
ldr.Errorf(s, "unexpected ARM64_RELOC_SUBTRACTOR reloc, must be followed by ARM64_RELOC_UNSIGNED at same offset")
break
}
su.SetRelocType(rIdx+1, objabi.R_PCREL)
su.SetRelocAdd(rIdx+1, r.Add()+int64(r.Off())+int64(r.Siz())-off)
// Remove the other relocation
su.SetRelocSiz(rIdx, 0)
return true
case objabi.MachoRelocOffset + ld.MACHO_ARM64_RELOC_BRANCH26*2 + pcrel:
su := ldr.MakeSymbolUpdater(s)
su.SetRelocType(rIdx, objabi.R_CALLARM64)

1
src/cmd/link/internal/ld/macho.go
View file

@ -106,6 +106,7 @@ const (
MACHO_ARM_RELOC_SECTDIFF = 2
MACHO_ARM_RELOC_BR24 = 5
MACHO_ARM64_RELOC_UNSIGNED = 0
MACHO_ARM64_RELOC_SUBTRACTOR = 1
MACHO_ARM64_RELOC_BRANCH26 = 2
MACHO_ARM64_RELOC_PAGE21 = 3
MACHO_ARM64_RELOC_PAGEOFF12 = 4