cmd/internal/obj: hoist fieldtrack code out of x86 back end

Change-Id: I38e59088c37426d914ce2b4dfc79f3d476e06f49
Reviewed-on: https://go-review.googlesource.com/19617Reviewed-by: David Crawshaw <crawshaw@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/internal/obj/obj.go

@@ -281,3 +281,21 @@ func linkgetline(ctxt *Link, lineno int32, f **LSym, l *int32) {
 func Linkprfile(ctxt *Link, line int) {
 	fmt.Printf("%s ", ctxt.LineHist.LineString(line))
 }
+
+func fieldtrack(ctxt *Link, cursym *LSym) {
+	p := cursym.Text
+	if p == nil || p.Link == nil { // handle external functions and ELF section symbols
+		return
+	}
+	ctxt.Cursym = cursym
+
+	for ; p != nil; p = p.Link {
+		if p.As == AUSEFIELD {
+			r := Addrel(ctxt.Cursym)
+			r.Off = 0
+			r.Siz = 0
+			r.Sym = p.From.Sym
+			r.Type = R_USEFIELD
+		}
+	}
+}

src/cmd/internal/obj/objfile.go

@@ -298,6 +298,7 @@ func Flushplist(ctxt *Link) {
 		ctxt.Arch.Follow(ctxt, s)
 		ctxt.Arch.Preprocess(ctxt, s)
 		ctxt.Arch.Assemble(ctxt, s)
+		fieldtrack(ctxt, s)
 		linkpcln(ctxt, s)
 	}
 

src/cmd/internal/obj/x86/asm6.go

@@ -4556,15 +4556,6 @@ func asmins(ctxt *obj.Link, p *obj.Prog) {
 	ctxt.Andptr = ctxt.And[:]
 	ctxt.Asmode = int(p.Mode)
 
-	if p.As == obj.AUSEFIELD {
-		r := obj.Addrel(ctxt.Cursym)
-		r.Off = 0
-		r.Siz = 0
-		r.Sym = p.From.Sym
-		r.Type = obj.R_USEFIELD
-		return
-	}
-
 	if ctxt.Headtype == obj.Hnacl && p.Mode == 32 {
 		switch p.As {
 		case obj.ARET: