cmd/link: always use symbol-targeted relocations on Mach-O

In Mach-O object files, there are two kinds of relocations:
"external" relocation, which targets a symbol, and "non-external"
relocation, which targets a section. For targeting symbols not in
the current object, we must use symbol-targeted relocations. For
targeting symbols defined in the current object, for some
relocation types, both kinds can be used. We currently use
section-targeted relocations for R_ADDR targeting locally defined
symbols.

Modern Apple toolchain seems to prefer symbol-targeted relocations.
Also, Apple's new linker, ld-prime, seems to not handle section-
targeted relocations well in some cases. So this CL switches to
always generate symbol-targeted relocations. This also simplifies
the code.

One exception is that DWARF tools seem to handle only section-
targeted relocations. So generate those in DWARF sections.

This CL supersedes CL 502616.

Fixes #60694.
For #61229.

Change-Id: I3b74df64f21114635061bcd89114392b3a2d588b
Reviewed-on: https://go-review.googlesource.com/c/go/+/503935
Reviewed-by: Than McIntosh <thanm@google.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

src/cmd/link/internal/amd64/asm.go

@@ -469,7 +469,7 @@ func machoreloc1(arch *sys.Arch, out *ld.OutBuf, ldr *loader.Loader, s loader.Sy
 	rs := r.Xsym
 	rt := r.Type
 
-	if rt == objabi.R_PCREL || rt == objabi.R_GOTPCREL || rt == objabi.R_CALL || ldr.SymType(rs) == sym.SHOSTOBJ || ldr.SymType(s) == sym.SINITARR {
+	if !ldr.SymType(s).IsDWARF() {
 		if ldr.SymDynid(rs) < 0 {
 			ldr.Errorf(s, "reloc %d (%s) to non-macho symbol %s type=%d (%s)", rt, sym.RelocName(arch, rt), ldr.SymName(rs), ldr.SymType(rs), ldr.SymType(rs))
 			return false

src/cmd/link/internal/arm64/asm.go

@@ -557,9 +557,11 @@ func machoreloc1(arch *sys.Arch, out *ld.OutBuf, ldr *loader.Loader, s loader.Sy
 	siz := r.Size
 	xadd := r.Xadd
 
-	if xadd != signext24(xadd) {
+	if xadd != signext24(xadd) && rt != objabi.R_ADDR {
 		// If the relocation target would overflow the addend, then target
 		// a linker-manufactured label symbol with a smaller addend instead.
+		// R_ADDR has full-width addend encoded in data content, so it doesn't
+		// use a label symbol.
 		label := ldr.Lookup(offsetLabelName(ldr, rs, xadd/machoRelocLimit*machoRelocLimit), ldr.SymVersion(rs))
 		if label != 0 {
 			xadd = ldr.SymValue(rs) + xadd - ldr.SymValue(label)
@@ -577,11 +579,7 @@ func machoreloc1(arch *sys.Arch, out *ld.OutBuf, ldr *loader.Loader, s loader.Sy
 		}
 	}
 
-	if rt == objabi.R_CALLARM64 ||
-		rt == objabi.R_ARM64_PCREL_LDST8 || rt == objabi.R_ARM64_PCREL_LDST16 ||
-		rt == objabi.R_ARM64_PCREL_LDST32 || rt == objabi.R_ARM64_PCREL_LDST64 ||
-		rt == objabi.R_ADDRARM64 || rt == objabi.R_ARM64_GOTPCREL ||
-		ldr.SymType(rs) == sym.SHOSTOBJ || ldr.SymType(s) == sym.SINITARR {
+	if !ldr.SymType(s).IsDWARF() {
 		if ldr.SymDynid(rs) < 0 {
 			ldr.Errorf(s, "reloc %d (%s) to non-macho symbol %s type=%d (%s)", rt, sym.RelocName(arch, rt), ldr.SymName(rs), ldr.SymType(rs), ldr.SymType(rs))
 			return false

src/cmd/link/internal/ld/data.go

@@ -368,9 +368,11 @@ func (st *relocSymState) relocsym(s loader.Sym, P []byte) {
 						o = 0
 					}
 				} else if target.IsDarwin() {
-					if ldr.SymType(rs) != sym.SHOSTOBJ && ldr.SymType(s) != sym.SINITARR {
-						// ld-prime drops the offset in data for SINITARR. We need to use
-						// symbol-targeted relocation. See also machoreloc1.
+					if ldr.SymType(s).IsDWARF() {
+						// We generally use symbol-targeted relocations.
+						// DWARF tools seem to only handle section-targeted relocations,
+						// so generate section-targeted relocations in DWARF sections.
+						// See also machoreloc1.
 						o += ldr.SymValue(rs)
 					}
 				} else if target.IsWindows() {

src/cmd/link/internal/sym/symkind.go

@@ -184,3 +184,7 @@ var RelROMap = map[SymKind]SymKind{
 func (t SymKind) IsData() bool {
 	return t == SDATA || t == SNOPTRDATA || t == SBSS || t == SNOPTRBSS
 }
+
+func (t SymKind) IsDWARF() bool {
+	return t >= SDWARFSECT && t <= SDWARFLINES
+}