runtime: use inlined function name for traceback elision

Currently, gentraceback decides which frames to print or elide when
unwinding inlined frames using only the name of the outermost
function. If the outermost function should be elided, then inlined
functions will also be elided, even if they shouldn't be.

This happens in practice in at least one situation. As of CL 258938,
exported Go functions (and functions they call) can now be inlined
into the generated _cgoexp_HASH_FN function. The runtime elides
_cgoexp_HASH_FN from tracebacks because it doesn't contain a ".".
Because of this bug, it also elides anything that was inlined into it.

This CL fixes this by synthesizing a funcInfo for the inlined
functions to pass to showframe.

Fixes #42754.

Change-Id: Ie6c663a4a1ac7f0d4beb1aa60bc26fc8cddd0f9d
Reviewed-on: https://go-review.googlesource.com/c/go/+/272131
Trust: Austin Clements <austin@google.com>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

src/runtime/crash_cgo_test.go

@@ -254,6 +254,24 @@ func TestCgoCrashTraceback(t *testing.T) {
 	}
 }
 
+func TestCgoCrashTracebackGo(t *testing.T) {
+	t.Parallel()
+	switch platform := runtime.GOOS + "/" + runtime.GOARCH; platform {
+	case "darwin/amd64":
+	case "linux/amd64":
+	case "linux/ppc64le":
+	default:
+		t.Skipf("not yet supported on %s", platform)
+	}
+	got := runTestProg(t, "testprogcgo", "CrashTracebackGo")
+	for i := 1; i <= 3; i++ {
+		want := fmt.Sprintf("main.h%d", i)
+		if !strings.Contains(got, want) {
+			t.Errorf("missing %s", want)
+		}
+	}
+}
+
 func TestCgoTracebackContext(t *testing.T) {
 	t.Parallel()
 	got := runTestProg(t, "testprogcgo", "TracebackContext")

src/runtime/stack_test.go

@@ -17,6 +17,7 @@ import (
 	"sync/atomic"
 	"testing"
 	"time"
+	_ "unsafe" // for go:linkname
 )
 
 // TestStackMem measures per-thread stack segment cache behavior.
@@ -851,3 +852,43 @@ func deferHeapAndStack(n int) (r int) {
 
 // Pass a value to escapeMe to force it to escape.
 var escapeMe = func(x interface{}) {}
+
+// Test that when F -> G is inlined and F is excluded from stack
+// traces, G still appears.
+func TestTracebackInlineExcluded(t *testing.T) {
+	defer func() {
+		recover()
+		buf := make([]byte, 4<<10)
+		stk := string(buf[:Stack(buf, false)])
+
+		t.Log(stk)
+
+		if not := "tracebackExcluded"; strings.Contains(stk, not) {
+			t.Errorf("found but did not expect %q", not)
+		}
+		if want := "tracebackNotExcluded"; !strings.Contains(stk, want) {
+			t.Errorf("expected %q in stack", want)
+		}
+	}()
+	tracebackExcluded()
+}
+
+// tracebackExcluded should be excluded from tracebacks. There are
+// various ways this could come up. Linking it to a "runtime." name is
+// rather synthetic, but it's easy and reliable. See issue #42754 for
+// one way this happened in real code.
+//
+//go:linkname tracebackExcluded runtime.tracebackExcluded
+//go:noinline
+func tracebackExcluded() {
+	// Call an inlined function that should not itself be excluded
+	// from tracebacks.
+	tracebackNotExcluded()
+}
+
+// tracebackNotExcluded should be inlined into tracebackExcluded, but
+// should not itself be excluded from the traceback.
+func tracebackNotExcluded() {
+	var x *int
+	*x = 0
+}

src/runtime/testdata/testprogcgo/traceback.go

@@ -12,6 +12,7 @@ package main
 #cgo CFLAGS: -g -O0
 
 // Defined in traceback_c.c.
+extern int crashInGo;
 int tracebackF1(void);
 void cgoTraceback(void* parg);
 void cgoSymbolizer(void* parg);
@@ -25,9 +26,29 @@ import (
 
 func init() {
 	register("CrashTraceback", CrashTraceback)
+	register("CrashTracebackGo", CrashTracebackGo)
 }
 
 func CrashTraceback() {
 	runtime.SetCgoTraceback(0, unsafe.Pointer(C.cgoTraceback), nil, unsafe.Pointer(C.cgoSymbolizer))
 	C.tracebackF1()
 }
+
+func CrashTracebackGo() {
+	C.crashInGo = 1
+	CrashTraceback()
+}
+
+//export h1
+func h1() {
+	h2()
+}
+
+func h2() {
+	h3()
+}
+
+func h3() {
+	var x *int
+	*x = 0
+}

src/runtime/testdata/testprogcgo/traceback_c.c

@@ -2,14 +2,21 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// The C definitions for traceback.go.
+// The C definitions for traceback.go. That file uses //export so
+// it can't put function definitions in the "C" import comment.
 
 #include <stdint.h>
 
 char *p;
 
+int crashInGo;
+extern void h1(void);
+
 int tracebackF3(void) {
-	*p = 0;
+	if (crashInGo)
+		h1();
+	else
+		*p = 0;
 	return 0;
 }
 

src/runtime/traceback.go

@@ -396,13 +396,21 @@ func gentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max in
 			// If there is inlining info, print the inner frames.
 			if inldata := funcdata(f, _FUNCDATA_InlTree); inldata != nil {
 				inltree := (*[1 << 20]inlinedCall)(inldata)
+				var inlFunc _func
+				inlFuncInfo := funcInfo{&inlFunc, f.datap}
 				for {
 					ix := pcdatavalue(f, _PCDATA_InlTreeIndex, tracepc, nil)
 					if ix < 0 {
 						break
 					}
-					if (flags&_TraceRuntimeFrames) != 0 || showframe(f, gp, nprint == 0, inltree[ix].funcID, lastFuncID) {
-						name := funcnameFromNameoff(f, inltree[ix].func_)
+
+					// Create a fake _func for the
+					// inlined function.
+					inlFunc.nameoff = inltree[ix].func_
+					inlFunc.funcID = inltree[ix].funcID
+
+					if (flags&_TraceRuntimeFrames) != 0 || showframe(inlFuncInfo, gp, nprint == 0, inlFuncInfo.funcID, lastFuncID) {
+						name := funcname(inlFuncInfo)
 						file, line := funcline(f, tracepc)
 						print(name, "(...)\n")
 						print("\t", file, ":", line, "\n")
@@ -811,6 +819,9 @@ func showframe(f funcInfo, gp *g, firstFrame bool, funcID, childID funcID) bool
 // showfuncinfo reports whether a function with the given characteristics should
 // be printed during a traceback.
 func showfuncinfo(f funcInfo, firstFrame bool, funcID, childID funcID) bool {
+	// Note that f may be a synthesized funcInfo for an inlined
+	// function, in which case only nameoff and funcID are set.
+
 	level, _, _ := gotraceback()
 	if level > 1 {
 		// Show all frames.