cmd/link: revert CL 89535: "fix up location lists for dsymutil"

This reverts commit 230b0ba.

Reason for revert: breaking the build.

Fixes #24165

Change-Id: I9d8dda59f97a47e5c436f1c061b34ced82bde8ec
Reviewed-on: https://go-review.googlesource.com/97575
Run-TryBot: Heschi Kreinick <[email protected]>
Reviewed-by: Robert Griesemer <[email protected]>
Reviewed-by: Joe Tsai <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>

Author: heschi

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

@@ -1759,10 +1759,6 @@ func collectlocs(ctxt *Link, syms []*sym.Symbol, units []*compilationUnit) []*sy
 					reloc.Sym.Attr |= sym.AttrReachable | sym.AttrNotInSymbolTable
 					syms = append(syms, reloc.Sym)
 					empty = false
-					// LLVM doesn't support base address entries. Strip them out so LLDB and dsymutil don't get confused.
-					if ctxt.HeadType == objabi.Hdarwin {
-						removeLocationListBaseAddress(ctxt, fn, reloc.Sym)
-					}
 					// One location list entry per function, but many relocations to it. Don't duplicate.
 					break
 				}
@@ -1779,73 +1775,6 @@ func collectlocs(ctxt *Link, syms []*sym.Symbol, units []*compilationUnit) []*sy
 	return syms
 }
 
-func removeLocationListBaseAddress(ctxt *Link, info, list *sym.Symbol) {
-	// The list symbol contains multiple lists, but they're all for the
-	// same function, and it's not empty.
-	fn := list.R[0].Sym
-
-	// Discard the relocations for the base address entries.
-	list.R = list.R[:0]
-
-	// Add relocations for each location entry's start and end addresses,
-	// so that the base address entries aren't necessary.
-	// We could remove them entirely, but that's more work for a relatively
-	// small size win. If dsymutil runs it'll throw them away anyway.
-
-	// relocate adds a CU-relative relocation to fn+addr at offset.
-	relocate := func(addr uint64, offset int) {
-		list.R = append(list.R, sym.Reloc{
-			Off:  int32(offset),
-			Siz:  uint8(ctxt.Arch.PtrSize),
-			Type: objabi.R_ADDRCUOFF,
-			Add:  int64(addr),
-			Sym:  fn,
-		})
-	}
-
-	for i := 0; i < len(list.P); {
-		first := readPtr(ctxt, list.P[i:])
-		second := readPtr(ctxt, list.P[i+ctxt.Arch.PtrSize:])
-
-		if first == 0 ||
-			first == ^uint64(0) ||
-			(ctxt.Arch.PtrSize == 4 && first == uint64(^uint32(0))) {
-			// Base address selection entry or end of list. Ignore.
-			i += ctxt.Arch.PtrSize * 2
-			continue
-		}
-
-		relocate(first, i)
-		relocate(second, i+ctxt.Arch.PtrSize)
-
-		// Skip past the actual location.
-		i += ctxt.Arch.PtrSize * 2
-		i += 2 + int(ctxt.Arch.ByteOrder.Uint16(list.P[i:]))
-	}
-
-	// Rewrite the DIE's relocations to point to the first location entry,
-	// not the now-useless base address selection entry.
-	for i := range info.R {
-		r := &info.R[i]
-		if r.Sym != list {
-			continue
-		}
-		r.Add += int64(2 * ctxt.Arch.PtrSize)
-	}
-}
-
-// Read a pointer-sized uint from the beginning of buf.
-func readPtr(ctxt *Link, buf []byte) uint64 {
-	switch ctxt.Arch.PtrSize {
-	case 4:
-		return uint64(ctxt.Arch.ByteOrder.Uint32(buf))
-	case 8:
-		return ctxt.Arch.ByteOrder.Uint64(buf)
-	default:
-		panic("unexpected pointer size")
-	}
-}
-
 /*
  *  Elf.
  */