cmd/internal/obj: remove Link.Tlsoffset

Nothing uses it any more.

Change-Id: I42ee7222b06b1a79b8b44894f3071752f9166d7a
Reviewed-on: https://go-review.googlesource.com/14193
Run-TryBot: Michael Hudson-Doyle <michael.hudson@canonical.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Dave Cheney <dave@cheney.net>

src/cmd/internal/obj/link.go

@@ -502,7 +502,6 @@ type Link struct {
 	Autosize           int32
 	Armsize            int32
 	Pc                 int64
-	Tlsoffset          int
 	Diag               func(string, ...interface{})
 	Mode               int
 	Cursym             *LSym

src/cmd/internal/obj/sym.go

@@ -105,66 +105,6 @@ func Linknew(arch *LinkArch) *Link {
 		log.Fatalf("unknown goos %s", Getgoos())
 	}
 
-	// Record thread-local storage offset.
-	// TODO(rsc): Move tlsoffset back into the linker.
-	switch ctxt.Headtype {
-	default:
-		log.Fatalf("unknown thread-local storage offset for %s", Headstr(ctxt.Headtype))
-
-	case Hplan9, Hwindows:
-		break
-
-		/*
-		 * ELF uses TLS offset negative from FS.
-		 * Translate 0(FS) and 8(FS) into -16(FS) and -8(FS).
-		 * Known to low-level assembly in package runtime and runtime/cgo.
-		 */
-	case Hlinux,
-		Hfreebsd,
-		Hnetbsd,
-		Hopenbsd,
-		Hdragonfly,
-		Hsolaris:
-		ctxt.Tlsoffset = -1 * ctxt.Arch.Ptrsize
-
-	case Hnacl:
-		switch ctxt.Arch.Thechar {
-		default:
-			log.Fatalf("unknown thread-local storage offset for nacl/%s", ctxt.Arch.Name)
-
-		case '5':
-			ctxt.Tlsoffset = 0
-
-		case '6':
-			ctxt.Tlsoffset = 0
-
-		case '8':
-			ctxt.Tlsoffset = -8
-		}
-
-		/*
-		 * OS X system constants - offset from 0(GS) to our TLS.
-		 * Explained in ../../runtime/cgo/gcc_darwin_*.c.
-		 */
-	case Hdarwin:
-		switch ctxt.Arch.Thechar {
-		default:
-			log.Fatalf("unknown thread-local storage offset for darwin/%s", ctxt.Arch.Name)
-
-		case '5':
-			ctxt.Tlsoffset = 0 // dummy value, not needed
-
-		case '6':
-			ctxt.Tlsoffset = 0x8a0
-
-		case '7':
-			ctxt.Tlsoffset = 0 // dummy value, not needed
-
-		case '8':
-			ctxt.Tlsoffset = 0x468
-		}
-	}
-
 	// On arm, record goarm.
 	if ctxt.Arch.Thechar == '5' {
 		p := Getgoarm()