runtime: fix Caller

log: add test of Caller

New regexp in log test is picky and will require some
maintenance, but it catches off-by-one mistakes too.

Fixes #710.

R=gri
CC=esko.luontola, golang-dev
https://golang.org/cl/887043

src/pkg/log/log_test.go

@@ -17,7 +17,7 @@ const (
 	Rdate         = `[0-9][0-9][0-9][0-9]/[0-9][0-9]/[0-9][0-9]`
 	Rtime         = `[0-9][0-9]:[0-9][0-9]:[0-9][0-9]`
 	Rmicroseconds = `\.[0-9][0-9][0-9][0-9][0-9][0-9]`
-	Rline         = `[0-9]+:`
+	Rline         = `(58|60):` // must update if the calls to l.Logf / l.Log below move
 	Rlongfile     = `.*/[A-Za-z0-9_\-]+\.go:` + Rline
 	Rshortfile    = `[A-Za-z0-9_\-]+\.go:` + Rline
 )

src/pkg/runtime/runtime.c

@@ -479,7 +479,7 @@ void
 {
 	Func *f;
 
-	if(callers(skip, &retpc, 1) == 0 || (f = findfunc(retpc-1)) == nil) {
+	if(callers(1+skip, &retpc, 1) == 0 || (f = findfunc(retpc-1)) == nil) {
 		retfile = emptystring;
 		retline = 0;
 		retbool = false;