cmd/compile: hide init functions in tracebacks

Treat compiler-generated init functions as wrappers, so they will not
be shown in tracebacks.

The exception to this rule is that we'd like to show the line number
of initializers for global variables in tracebacks. In order to
preserve line numbers for those cases, separate out the code for those
initializers into a separate function (which is not marked as
autogenerated).

This CL makes the go binary 0.2% bigger.

Fixes #29919

Change-Id: I0f1fbfc03d10d764ce3a8ddb48fb387ca8453386
Reviewed-on: https://go-review.googlesource.com/c/159717
Run-TryBot: Keith Randall <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>

Author: randall77

src/cmd/compile/internal/gc/init.go

@@ -57,6 +57,9 @@ func anyinit(n []*Node) bool {
 
 // fninit hand-crafts package initialization code.
 //
+//      func init.ializers() {                          (0)
+//              <init stmts>
+//      }
 //      var initdone· uint8                             (1)
 //      func init() {                                   (2)
 //              if initdone· > 1 {                      (3)
@@ -68,7 +71,7 @@ func anyinit(n []*Node) bool {
 //              initdone· = 1                           (5)
 //              // over all matching imported symbols
 //                      <pkg>.init()                    (6)
-//              { <init stmts> }                        (7)
+//              init.ializers()                         (7)
 //              init.<n>() // if any                    (8)
 //              initdone· = 2                           (9)
 //              return                                  (10)
@@ -80,6 +83,27 @@ func fninit(n []*Node) {
 		return
 	}
 
+	// (0)
+	// Make a function that contains all the initialization statements.
+	// This is a separate function because we want it to appear in
+	// stack traces, where the init function itself does not.
+	var initializers *types.Sym
+	if len(nf) > 0 {
+		lineno = nf[0].Pos // prolog/epilog gets line number of first init stmt
+		initializers = lookup("init.ializers")
+		disableExport(initializers)
+		fn := dclfunc(initializers, nod(OTFUNC, nil, nil))
+		fn.Nbody.Set(nf)
+		funcbody()
+
+		fn = typecheck(fn, ctxStmt)
+		Curfn = fn
+		typecheckslice(nf, ctxStmt)
+		Curfn = nil
+		funccompile(fn)
+		lineno = autogeneratedPos
+	}
+
 	var r []*Node
 
 	// (1)
@@ -130,7 +154,11 @@ func fninit(n []*Node) {
 	}
 
 	// (7)
-	r = append(r, nf...)
+	if initializers != nil {
+		n := newname(initializers)
+		addvar(n, functype(nil, nil, nil), PFUNC)
+		r = append(r, nod(OCALL, n, nil))
+	}
 
 	// (8)
 

src/cmd/internal/objabi/funcid.go

@@ -83,7 +83,7 @@ func GetFuncID(name, file string) FuncID {
 	case "runtime.panicwrap":
 		return FuncID_panicwrap
 	}
-	if file == "<autogenerated>" && !strings.HasSuffix(name, ".init") {
+	if file == "<autogenerated>" {
 		return FuncID_wrapper
 	}
 	if strings.HasPrefix(name, "runtime.call") {

test/fixedbugs/issue29919.dir/a.go

@@ -0,0 +1,75 @@
+// Copyright 2019 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.
+
+// Make sure tracebacks from initialization code are reported correctly.
+
+package a
+
+import (
+	"fmt"
+	"runtime"
+	"strings"
+)
+
+var x = f() // line 15
+
+func f() int {
+	var b [4096]byte
+	n := runtime.Stack(b[:], false) // line 19
+	s := string(b[:n])
+	var pcs [10]uintptr
+	n = runtime.Callers(1, pcs[:]) // line 22
+
+	// Check the Stack results.
+	if debug {
+		println(s)
+	}
+	if strings.Contains(s, "autogenerated") {
+		panic("autogenerated code in traceback")
+	}
+	if !strings.Contains(s, "a.go:15") {
+		panic("missing a.go:15")
+	}
+	if !strings.Contains(s, "a.go:19") {
+		panic("missing a.go:19")
+	}
+	if !strings.Contains(s, "a.init.ializers") {
+		panic("missing a.init.ializers")
+	}
+
+	// Check the CallersFrames results.
+	if debug {
+		iter := runtime.CallersFrames(pcs[:n])
+		for {
+			f, more := iter.Next()
+			fmt.Printf("%s %s:%d\n", f.Function, f.File, f.Line)
+			if !more {
+				break
+			}
+		}
+	}
+	iter := runtime.CallersFrames(pcs[:n])
+	f, more := iter.Next()
+	if f.Function != "a.f" || !strings.HasSuffix(f.File, "a.go") || f.Line != 22 {
+		panic(fmt.Sprintf("bad f %v\n", f))
+	}
+	if !more {
+		panic("traceback truncated after f")
+	}
+	f, more = iter.Next()
+	if f.Function != "a.init.ializers" || !strings.HasSuffix(f.File, "a.go") || f.Line != 15 {
+		panic(fmt.Sprintf("bad init.ializers %v\n", f))
+	}
+	if !more {
+		panic("traceback truncated after init.ializers")
+	}
+	f, _ = iter.Next()
+	if f.Function != "runtime.main" {
+		panic("runtime.main missing")
+	}
+
+	return 0
+}
+
+const debug = false

test/fixedbugs/issue29919.dir/main.go

@@ -0,0 +1,10 @@
+// Copyright 2019 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 _ "./a"
+
+func main() {
+}

test/fixedbugs/issue29919.go

@@ -0,0 +1,9 @@
+// rundir
+
+// Copyright 2019 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.
+
+// Make sure tracebacks from initialization code are reported correctly.
+
+package ignored