[release-branch.go1.12] cmd/link: put shlib ".type" functions in internal ABI

These functions are compiler generated, and as such are only available
in the internal ABI. Doing this avoids generating an alias symbol.
Doing that avoids confusion between unmangled and mangled type symbols.

Updates #30768
Fixes #33040

Change-Id: I8aba3934ffa994b1a19fc442cfe3e05642792a25
Reviewed-on: https://go-review.googlesource.com/c/go/+/186278
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>

misc/cgo/testshared/shared_test.go

@@ -917,3 +917,10 @@ func TestTestInstalledShared(t *testing.T) {
 func TestGeneratedMethod(t *testing.T) {
 	goCmd(t, "install", "-buildmode=shared", "-linkshared", "issue25065")
 }
+
+// Test use of shared library struct with generated hash function.
+// Issue 30768.
+func TestGeneratedHash(t *testing.T) {
+	goCmd(nil, "install", "-buildmode=shared", "-linkshared", "issue30768/issue30768lib")
+	goCmd(nil, "test", "-linkshared", "issue30768")
+}

misc/cgo/testshared/src/issue30768/issue30768lib/lib.go

+// 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 issue30768lib
+
+// S is a struct that requires a generated hash function.
+type S struct {
+	A string
+	B int
+}

misc/cgo/testshared/src/issue30768/x_test.go

+// 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 issue30768_test
+
+import (
+	"testing"
+
+	"issue30768/issue30768lib"
+)
+
+type s struct {
+	s issue30768lib.S
+}
+
+func Test30768(t *testing.T) {
+	// Calling t.Log will convert S to an empty interface,
+	// which will force a reference to the generated hash function,
+	// defined in the shared library.
+	t.Log(s{})
+}

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

@@ -1802,7 +1802,15 @@ func ldshlibsyms(ctxt *Link, shlib string) {
 		if elf.ST_TYPE(elfsym.Info) == elf.STT_NOTYPE || elf.ST_TYPE(elfsym.Info) == elf.STT_SECTION {
 			continue
 		}
-		lsym := ctxt.Syms.Lookup(elfsym.Name, 0)
+
+		// Symbols whose names start with "type." are compiler
+		// generated, so make functions with that prefix internal.
+		ver := 0
+		if elf.ST_TYPE(elfsym.Info) == elf.STT_FUNC && strings.HasPrefix(elfsym.Name, "type.") {
+			ver = sym.SymVerABIInternal
+		}
+
+		lsym := ctxt.Syms.Lookup(elfsym.Name, ver)
 		// Because loadlib above loads all .a files before loading any shared
 		// libraries, any non-dynimport symbols we find that duplicate symbols
 		// already loaded should be ignored (the symbols from the .a files
@@ -1830,7 +1838,7 @@ func ldshlibsyms(ctxt *Link, shlib string) {
 		// the ABIs are actually different. We might have to
 		// mangle Go function names in the .so to include the
 		// ABI.
-		if elf.ST_TYPE(elfsym.Info) == elf.STT_FUNC {
+		if elf.ST_TYPE(elfsym.Info) == elf.STT_FUNC && ver == 0 {
 			alias := ctxt.Syms.Lookup(elfsym.Name, sym.SymVerABIInternal)
 			if alias.Type != 0 {
 				continue