cmd/link: export specialized variants of runtime._type to debug_info

The reflect package can be used to create new types at runtime, these
types will have runtime._type entries describing them but no entry in
debug_info (obviously).

A debugger that wanted to print the value of variables with such types
will have to read the runtime._type directly, however the
"specializations" of runtime._type (runtime.slicetype, runtime.maptype,
etc) are not exported to debug_info, besides runtime.interfacetype.

All those types (i.e. runtime.slicetype, runtime.maptype, etc) should
be exported to debug_info so that debuggers don't have to hard-code
their description.

Fixes #19602

Change-Id: I086d523a4421a4ed964e16bc3c2274319a98b45b
Reviewed-on: https://go-review.googlesource.com/38350
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>

src/cmd/link/internal/ld/dwarf.go

@@ -1521,10 +1521,20 @@ func dwarfgeneratedebugsyms(ctxt *Link) {
 	}
 
 	// Needed by the prettyprinter code for interface inspection.
-	defgotype(ctxt, lookupOrDiag(ctxt, "type.runtime._type"))
+	for _, typ := range []string{
-
+		"type.runtime._type",
-	defgotype(ctxt, lookupOrDiag(ctxt, "type.runtime.interfacetype"))
+		"type.runtime.arraytype",
-	defgotype(ctxt, lookupOrDiag(ctxt, "type.runtime.itab"))
+		"type.runtime.chantype",
+		"type.runtime.functype",
+		"type.runtime.maptype",
+		"type.runtime.ptrtype",
+		"type.runtime.slicetype",
+		"type.runtime.structtype",
+		"type.runtime.interfacetype",
+		"type.runtime.itab",
+		"type.runtime.imethod"} {
+		defgotype(ctxt, lookupOrDiag(ctxt, typ))
+	}
 
 	genasmsym(ctxt, defdwsymb)
 

src/cmd/link/internal/ld/dwarf_test.go

@@ -0,0 +1,90 @@
+// Copyright 2017 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 ld
+
+import (
+	objfilepkg "cmd/internal/objfile" // renamed to avoid conflict with objfile function
+	"debug/dwarf"
+	"internal/testenv"
+	"io/ioutil"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"testing"
+)
+
+func TestRuntimeTypeDIEs(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+	dir, err := ioutil.TempDir("", "TestRuntimeTypeDIEs")
+	if err != nil {
+		t.Fatalf("could not create directory: %v", err)
+	}
+	defer os.RemoveAll(dir)
+
+	f := gobuild(t, dir, `package main; func main() { }`)
+	defer f.Close()
+
+	dwarf, err := f.DWARF()
+	if err != nil {
+		t.Fatalf("error reading DWARF: %v", err)
+	}
+
+	want := map[string]bool{
+		"runtime._type":         true,
+		"runtime.arraytype":     true,
+		"runtime.chantype":      true,
+		"runtime.functype":      true,
+		"runtime.maptype":       true,
+		"runtime.ptrtype":       true,
+		"runtime.slicetype":     true,
+		"runtime.structtype":    true,
+		"runtime.interfacetype": true,
+		"runtime.itab":          true,
+		"runtime.imethod":       true,
+	}
+
+	found := findTypes(t, dwarf, want)
+	if len(found) != len(want) {
+		t.Errorf("found %v, want %v", found, want)
+	}
+}
+
+func findTypes(t *testing.T, dw *dwarf.Data, want map[string]bool) (found map[string]bool) {
+	found = make(map[string]bool)
+	rdr := dw.Reader()
+	for entry, err := rdr.Next(); entry != nil; entry, err = rdr.Next() {
+		if err != nil {
+			t.Fatalf("error reading DWARF: %v", err)
+		}
+		switch entry.Tag {
+		case dwarf.TagTypedef:
+			if name, ok := entry.Val(dwarf.AttrName).(string); ok && want[name] {
+				found[name] = true
+			}
+		}
+	}
+	return
+}
+
+func gobuild(t *testing.T, dir string, testfile string) *objfilepkg.File {
+	src := filepath.Join(dir, "test.go")
+	dst := filepath.Join(dir, "out")
+
+	if err := ioutil.WriteFile(src, []byte(testfile), 0666); err != nil {
+		t.Fatal(err)
+	}
+
+	cmd := exec.Command(testenv.GoToolPath(t), "build", "-o", dst, src)
+	if b, err := cmd.CombinedOutput(); err != nil {
+		t.Logf("build: %s\n", b)
+		t.Fatalf("build error: %v", err)
+	}
+
+	f, err := objfilepkg.Open(dst)
+	if err != nil {
+		t.Fatal(err)
+	}
+	return f
+}