runtime: delete duplicate implementation of pcln walker

It's hard enough to get right once.

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/5533073

src/pkg/runtime/extern.go

@@ -59,51 +59,12 @@ func (f *Func) Entry() uintptr { return f.entry }
 // The result will not be accurate if pc is not a program
 // counter within f.
 func (f *Func) FileLine(pc uintptr) (file string, line int) {
-	// NOTE(rsc): If you edit this function, also edit
-	// symtab.c:/^funcline.  That function also has the
-	// comments explaining the logic.
-	targetpc := pc
-
-	var pcQuant uintptr = 1
-	if GOARCH == "arm" {
-		pcQuant = 4
-	}
-
-	p := f.pcln
-	pc = f.pc0
-	line = int(f.ln0)
-	i := 0
-	//print("FileLine start pc=", pc, " targetpc=", targetpc, " line=", line,
-	//	" tab=", p, " ", p[0], " quant=", pcQuant, " GOARCH=", GOARCH, "\n")
-	for {
-		for i < len(p) && p[i] > 128 {
-			pc += pcQuant * uintptr(p[i]-128)
-			i++
-		}
-		//print("pc<", pc, " targetpc=", targetpc, " line=", line, "\n")
-		if pc > targetpc || i >= len(p) {
-			break
-		}
-		if p[i] == 0 {
-			if i+5 > len(p) {
-				break
-			}
-			line += int(p[i+1]<<24) | int(p[i+2]<<16) | int(p[i+3]<<8) | int(p[i+4])
-			i += 5
-		} else if p[i] <= 64 {
-			line += int(p[i])
-			i++
-		} else {
-			line -= int(p[i] - 64)
-			i++
-		}
-		//print("pc=", pc, " targetpc=", targetpc, " line=", line, "\n")
-		pc += pcQuant
-	}
-	file = f.src
-	return
+	return funcline_go(f, pc)
 }
 
+// implemented in symtab.c
+func funcline_go(*Func, uintptr) (string, int)
+
 // mid returns the current os thread (m) id.
 func mid() uint32
 

src/pkg/runtime/symtab.c

@@ -381,6 +381,15 @@ runtime·funcline(Func *f, uintptr targetpc)
 	return line;
 }
 
+void
+runtime·funcline_go(Func *f, uintptr targetpc, String retfile, int32 retline)
+{
+	retfile = f->src;
+	retline = runtime·funcline(f, targetpc);
+	FLUSH(&retfile);
+	FLUSH(&retline);
+}
+
 static void
 buildfuncs(void)
 {