1 files changed, 37 insertions, 1 deletions
diff --git a/src/runtime/error.go b/src/runtime/error.go
index 0238c5e592..f5b015c091 100644
--- a/src/runtime/error.go
+++ b/src/runtime/error.go
@@ -4,6 +4,8 @@
 
 package runtime
 
+import _ "unsafe" // for go:linkname
+
 // The Error interface identifies a run time error.
 type Error interface {
 	error
@@ -91,7 +93,41 @@ func printany(i interface{}) {
 	}
 }
 
+// strings.IndexByte is implemented in runtime/asm_$goarch.s
+// but amusingly we need go:linkname to get access to it here in the runtime.
+//go:linkname stringsIndexByte strings.IndexByte
+func stringsIndexByte(s string, c byte) int
+
 // called from generated code
-func panicwrap(pkg, typ, meth string) {
+func panicwrap() {
+	pc := make([]uintptr, 1)
+	n := Callers(2, pc)
+	if n == 0 {
+		throw("panicwrap: Callers failed")
+	}
+	frames := CallersFrames(pc)
+	frame, _ := frames.Next()
+	name := frame.Function
+	// name is something like "main.(*T).F".
+	// We want to extract pkg ("main"), typ ("T"), and meth ("F").
+	// Do it by finding the parens.
+	i := stringsIndexByte(name, '(')
+	if i < 0 {
+		throw("panicwrap: no ( in " + frame.Function)
+	}
+	pkg := name[:i-1]
+	if i+2 >= len(name) || name[i-1:i+2] != ".(*" {
+		throw("panicwrap: unexpected string after package name: " + frame.Function)
+	}
+	name = name[i+2:]
+	i = stringsIndexByte(name, ')')
+	if i < 0 {
+		throw("panicwrap: no ) in " + frame.Function)
+	}
+	if i+2 >= len(name) || name[i:i+2] != ")." {
+		throw("panicwrap: unexpected string after type name: " + frame.Function)
+	}
+	typ := name[:i]
+	meth := name[i+2:]
 	panic(plainError("value method " + pkg + "." + typ + "." + meth + " called using nil *" + typ + " pointer"))
 }