runtime: more detailed panic traces, line number work

Follow morestack, so that crashes during a stack split
give complete traces.  Also mark stack segment boundaries
as an aid to debugging.

Correct various line number bugs with yet another attempt
at interpreting the pc/ln table.  This one has a chance at
being correct, because I based it on reading src/cmd/ld/lib.c
instead of on reading the documentation.

Fixes #1138.
Fixes #1430.
Fixes #1461.

throw: runtime: split stack overflow

runtime.throw+0x3e /home/rsc/g/go2/src/pkg/runtime/runtime.c:78
        runtime.throw(0x81880af, 0xf75c8b18)
runtime.newstack+0xad /home/rsc/g/go2/src/pkg/runtime/proc.c:728
        runtime.newstack()
runtime.morestack+0x4f /home/rsc/g/go2/src/pkg/runtime/386/asm.s:184
        runtime.morestack()
----- morestack called from stack: -----
runtime.new+0x1a /home/rsc/g/go2/src/pkg/runtime/malloc.c:288
        runtime.new(0x1, 0x0, 0x0)
gongo.makeBoard+0x33 /tmp/Gongo/gongo_robot_test.go:344
        gongo.makeBoard(0x809d238, 0x1, 0xf76092c8, 0x1)
----- stack segment boundary -----
gongo.checkEasyScore+0xcc /tmp/Gongo/gongo_robot_test.go:287
        gongo.checkEasyScore(0xf764b710, 0x0, 0x809d238, 0x1)
gongo.TestEasyScore+0x8c /tmp/Gongo/gongo_robot_test.go:255
        gongo.TestEasyScore(0xf764b710, 0x818a990)
testing.tRunner+0x2f /home/rsc/g/go2/src/pkg/testing/testing.go:132
        testing.tRunner(0xf764b710, 0xf763b5dc, 0x0)
runtime.goexit /home/rsc/g/go2/src/pkg/runtime/proc.c:149
        runtime.goexit()

R=ken2, r
CC=golang-dev
https://golang.org/cl/4000053

1 files changed, 27 insertions, 11 deletions

diff --git a/src/pkg/runtime/extern.go b/src/pkg/runtime/extern.go
index dba28324c4..c6e664abbb 100644
--- a/src/pkg/runtime/extern.go
+++ b/src/pkg/runtime/extern.go
@@ -60,31 +60,47 @@ func (f *Func) Entry() uintptr { return f.entry }
 // 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.
+	// symtab.c:/^funcline.  That function also has the
+	// comments explaining the logic.
+	targetpc := pc
+
 	var pcQuant uintptr = 1
 	if GOARCH == "arm" {
 		pcQuant = 4
 	}
 
-	targetpc := pc
 	p := f.pcln
 	pc = f.pc0
 	line = int(f.ln0)
-	file = f.src
-	for i := 0; i < len(p) && pc <= targetpc; i++ {
-		switch {
-		case p[i] == 0:
+	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 += 4
-		case p[i] <= 64:
+			i += 5
+		} else if p[i] <= 64 {
 			line += int(p[i])
-		case p[i] <= 128:
+			i++
+		} else {
 			line -= int(p[i] - 64)
-		default:
-			pc += pcQuant * uintptr(p[i]-129)
+			i++
 		}
+		//print("pc=", pc, " targetpc=", targetpc, " line=", line, "\n")
 		pc += pcQuant
 	}
+	file = f.src
 	return
 }