runtime: hide <autogenerated> methods from call stack

The compiler generates wrapper methods to forward interface method
calls (which are always pointer-based) to value methods. These
wrappers appear in the call stack even though they are an
implementation detail. This leaves ugly "<autogenerated>" functions in
stack traces and can throw off skip counts for stack traces.

Fix this by considering these runtime frames in printed stack traces
so they will only be printed if runtime frames are being printed, and
by eliding them from the call stack expansion used by CallersFrames
and Caller.

This removes the test for issue 4388 since that was checking that
"<autogenerated>" appeared in the stack trace instead of something
even weirder. We replace it with various runtime package tests.

Fixes #16723.

Change-Id: Ice3f118c66f254bb71478a664d62ab3fc7125819
Reviewed-on: https://go-review.googlesource.com/45412
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/runtime/stack_test.go

@@ -5,6 +5,7 @@
 package runtime_test
 
 import (
+	"fmt"
 	. "runtime"
 	"strings"
 	"sync"
@@ -627,3 +628,60 @@ func count23(n int) int {
 	}
 	return 1 + count1(n-1)
 }
+
+type structWithMethod struct{}
+
+func (s structWithMethod) caller() string {
+	_, file, line, ok := Caller(1)
+	if !ok {
+		panic("Caller failed")
+	}
+	return fmt.Sprintf("%s:%d", file, line)
+}
+
+func (s structWithMethod) callers() []uintptr {
+	pc := make([]uintptr, 16)
+	return pc[:Callers(0, pc)]
+}
+
+func (s structWithMethod) stack() string {
+	buf := make([]byte, 4<<10)
+	return string(buf[:Stack(buf, false)])
+}
+
+func TestStackWrapperCaller(t *testing.T) {
+	var d structWithMethod
+	// Force the compiler to construct a wrapper method.
+	wrapper := (*structWithMethod).caller
+	// Check that the wrapper doesn't affect the stack trace.
+	if dc, ic := d.caller(), wrapper(&d); dc != ic {
+		t.Fatalf("direct caller %q != indirect caller %q", dc, ic)
+	}
+}
+
+func TestStackWrapperCallers(t *testing.T) {
+	var d structWithMethod
+	wrapper := (*structWithMethod).callers
+	// Check that <autogenerated> doesn't appear in the stack trace.
+	pcs := wrapper(&d)
+	frames := CallersFrames(pcs)
+	for {
+		fr, more := frames.Next()
+		if fr.File == "<autogenerated>" {
+			t.Fatalf("<autogenerated> appears in stack trace: %+v", fr)
+		}
+		if !more {
+			break
+		}
+	}
+}
+
+func TestStackWrapperStack(t *testing.T) {
+	var d structWithMethod
+	wrapper := (*structWithMethod).stack
+	// Check that <autogenerated> doesn't appear in the stack trace.
+	stk := wrapper(&d)
+	if strings.Contains(stk, "<autogenerated>") {
+		t.Fatalf("<autogenerated> appears in stack trace:\n%s", stk)
+	}
+}

src/runtime/symtab.go

@@ -118,6 +118,7 @@ func (ci *Frames) Next() (frame Frame, more bool) {
 
 func (se *stackExpander) next(callers []uintptr) (ncallers []uintptr, frame Frame, more bool) {
 	ncallers = callers
+again:
 	if !se.pcExpander.more {
 		// Expand the next PC.
 		if len(ncallers) == 0 {
@@ -144,6 +145,13 @@ func (se *stackExpander) next(callers []uintptr) (ncallers []uintptr, frame Fram
 	}
 
 	frame = se.pcExpander.next()
+	if frame.File == "<autogenerated>" {
+		// Ignore autogenerated functions such as pointer
+		// method forwarding functions. These are an
+		// implementation detail that doesn't reflect the
+		// source code.
+		goto again
+	}
 	return ncallers, frame, se.pcExpander.more || len(ncallers) > 0
 }
 

src/runtime/traceback.go

@@ -733,7 +733,13 @@ func showframe(f funcInfo, gp *g, firstFrame bool) bool {
 		return true
 	}
 	level, _, _ := gotraceback()
+	if level > 1 {
+		// Show all frames.
+		return true
+	}
+
 	name := funcname(f)
+	file, _ := funcline(f, f.entry)
 
 	// Special case: always show runtime.gopanic frame
 	// in the middle of a stack trace, so that we can
@@ -744,7 +750,7 @@ func showframe(f funcInfo, gp *g, firstFrame bool) bool {
 		return true
 	}
 
-	return level > 1 || f.valid() && contains(name, ".") && (!hasprefix(name, "runtime.") || isExportedRuntime(name))
+	return f.valid() && contains(name, ".") && (!hasprefix(name, "runtime.") || isExportedRuntime(name)) && file != "<autogenerated>"
 }
 
 // isExportedRuntime reports whether name is an exported runtime function.

test/fixedbugs/issue4388.go

-// run
-
-// Copyright 2014 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package main
-
-import (
-	"fmt"
-	"io"
-	"runtime"
-)
-
-type T struct {
-	io.Closer
-}
-
-func f1() {
-	// The 5 here and below depends on the number of internal runtime frames
-	// that sit between a deferred function called during panic and
-	// the original frame. If that changes, this test will start failing and
-	// the number here will need to be updated.
-	defer checkLine(5)
-	var t *T
-	var c io.Closer = t
-	c.Close()
-}
-
-func f2() {
-	defer checkLine(5)
-	var t T
-	var c io.Closer = t
-	c.Close()
-}
-
-func main() {
-	f1()
-	f2()
-}
-
-func checkLine(n int) {
-	if err := recover(); err == nil {
-		panic("did not panic")
-	}
-	var file string
-	var line int
-	for i := 1; i <= n; i++ {
-		_, file, line, _ = runtime.Caller(i)
-		if file != "<autogenerated>" || line != 1 {
-			continue
-		}
-		return
-	}
-	panic(fmt.Sprintf("expected <autogenerated>:1 have %s:%d", file, line))
-}