all: add GOOS=android

As android and linux have significant overlap, and
because build tags are a poor way to represent an
OS target, this CL introduces an exception into
go/build: linux is treated as a synonym for android
when matching files.

http://golang.org/s/go14android
https://groups.google.com/forum/#!topic/golang-dev/P1ATVp1mun0

LGTM=rsc, minux
R=golang-codereviews, mikioh.mikioh, dave, aram, minux, gobot, rsc, aram.h, elias.naur, iant
CC=golang-codereviews, rsc
https://golang.org/cl/105270043

src/cmd/dist/build.c

@@ -56,6 +56,7 @@ static char *okgoos[] = {
 	"darwin",
 	"dragonfly",
 	"linux",
+	"android",
 	"solaris",
 	"freebsd",
 	"nacl",
@@ -1149,7 +1150,7 @@ matchfield(char *f)
 
 	p = xstrrchr(f, ',');
 	if(p == nil)
-		return streq(f, goos) || streq(f, goarch) || streq(f, "cmd_go_bootstrap") || streq(f, "go1.1");
+		return streq(f, goos) || streq(f, goarch) || streq(f, "cmd_go_bootstrap") || streq(f, "go1.1") || (streq(goos, "android") && streq(f, "linux"));
 	*p = 0;
 	res = matchfield(f) && matchfield(p+1);
 	*p = ',';

src/cmd/dist/buildruntime.c

@@ -108,10 +108,14 @@ mkzgoos(char *dir, char *file)
 	
 	binit(&b);
 	binit(&out);
+
+	bwritestr(&out, "// auto generated by go tool dist\n\n");
+
+	if (streq(goos, "linux")) {
+		bwritestr(&out, "// +build !android\n\n");
+	}
 	
 	bwritestr(&out, bprintf(&b,
-		"// auto generated by go tool dist\n"
-		"\n"
 		"package runtime\n"
 		"\n"
 		"const theGoos = `%s`\n", goos));

src/liblink/sym.c

@@ -49,6 +49,7 @@ static struct {
 	"elf",		Helf,
 	"freebsd",	Hfreebsd,
 	"linux",	Hlinux,
+	"android",	Hlinux,
 	"nacl",		Hnacl,
 	"netbsd",	Hnetbsd,
 	"openbsd",	Hopenbsd,

src/pkg/go/build/build.go

@@ -268,6 +268,9 @@ var cgoEnabled = map[string]bool{
 	"linux/386":       true,
 	"linux/amd64":     true,
 	"linux/arm":       true,
+	"android/386":     true,
+	"android/amd64":   true,
+	"android/arm":     true,
 	"netbsd/386":      true,
 	"netbsd/amd64":    true,
 	"netbsd/arm":      true,
@@ -1124,6 +1127,9 @@ func (ctxt *Context) match(name string, allTags map[string]bool) bool {
 	if name == ctxt.GOOS || name == ctxt.GOARCH || name == ctxt.Compiler {
 		return true
 	}
+	if ctxt.GOOS == "android" && name == "linux" {
+		return true
+	}
 
 	// other tags
 	for _, tag := range ctxt.BuildTags {
@@ -1151,6 +1157,7 @@ func (ctxt *Context) match(name string, allTags map[string]bool) bool {
 //     name_$(GOARCH)_test.*
 //     name_$(GOOS)_$(GOARCH)_test.*
 //
+// An exception: if GOOS=android, then files with GOOS=linux are also matched.
 func (ctxt *Context) goodOSArchFile(name string, allTags map[string]bool) bool {
 	if dot := strings.Index(name, "."); dot != -1 {
 		name = name[:dot]
@@ -1165,12 +1172,21 @@ func (ctxt *Context) goodOSArchFile(name string, allTags map[string]bool) bool {
 			allTags[l[n-2]] = true
 			allTags[l[n-1]] = true
 		}
-		return l[n-2] == ctxt.GOOS && l[n-1] == ctxt.GOARCH
+		if l[n-1] != ctxt.GOARCH {
+			return false
+		}
+		if ctxt.GOOS == "android" && l[n-2] == "linux" {
+			return true
+		}
+		return l[n-2] == ctxt.GOOS
 	}
 	if n >= 1 && knownOS[l[n-1]] {
 		if allTags != nil {
 			allTags[l[n-1]] = true
 		}
+		if ctxt.GOOS == "android" && l[n-1] == "linux" {
+			return true
+		}
 		return l[n-1] == ctxt.GOOS
 	}
 	if n >= 1 && knownArch[l[n-1]] {

src/pkg/go/build/build_test.go

@@ -153,22 +153,31 @@ func (r readNopCloser) Close() error {
 	return nil
 }
 
+var (
+	ctxtP9      = Context{GOARCH: "arm", GOOS: "plan9"}
+	ctxtAndroid = Context{GOARCH: "arm", GOOS: "android"}
+)
+
 var matchFileTests = []struct {
+	ctxt  Context
 	name  string
 	data  string
 	match bool
 }{
-	{"foo_arm.go", "", true},
-	{"foo1_arm.go", "// +build linux\n\npackage main\n", false},
-	{"foo_darwin.go", "", false},
-	{"foo.go", "", true},
-	{"foo1.go", "// +build linux\n\npackage main\n", false},
-	{"foo.badsuffix", "", false},
+	{ctxtP9, "foo_arm.go", "", true},
+	{ctxtP9, "foo1_arm.go", "// +build linux\n\npackage main\n", false},
+	{ctxtP9, "foo_darwin.go", "", false},
+	{ctxtP9, "foo.go", "", true},
+	{ctxtP9, "foo1.go", "// +build linux\n\npackage main\n", false},
+	{ctxtP9, "foo.badsuffix", "", false},
+	{ctxtAndroid, "foo_linux.go", "", true},
+	{ctxtAndroid, "foo_android.go", "", true},
+	{ctxtAndroid, "foo_plan9.go", "", false},
 }
 
 func TestMatchFile(t *testing.T) {
 	for _, tt := range matchFileTests {
-		ctxt := Context{GOARCH: "arm", GOOS: "plan9"}
+		ctxt := tt.ctxt
 		ctxt.OpenFile = func(path string) (r io.ReadCloser, err error) {
 			if path != "x+"+tt.name {
 				t.Fatalf("OpenFile asked for %q, expected %q", path, "x+"+tt.name)

src/pkg/go/build/doc.go

@@ -134,4 +134,7 @@
 // building the package for Windows; similarly, math_386.s will be included
 // only when building the package for 32-bit x86.
 //
+// Using GOOS=android matches build tags and files as for GOOS=linux
+// in addition to android tags and files.
+//
 package build

src/pkg/go/build/syslist.go

@@ -4,5 +4,5 @@
 
 package build
 
-const goosList = "darwin dragonfly freebsd linux nacl netbsd openbsd plan9 solaris windows "
+const goosList = "android darwin dragonfly freebsd linux nacl netbsd openbsd plan9 solaris windows "
 const goarchList = "386 amd64 amd64p32 arm "

src/pkg/runtime/defs_android_arm.h

+// TODO: Generate using cgo like defs_linux_{386,amd64}.h
+
+#include "defs_linux_arm.h"

src/pkg/runtime/os_android.h

+#include "os_linux.h"

src/pkg/runtime/rt0_android_arm.s

+// 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.
+
+#include "../../cmd/ld/textflag.h"
+
+TEXT _rt0_arm_android(SB),NOSPLIT,$-4
+	MOVW		(R13), R0      // argc
+	MOVW		$4(R13), R1    // argv
+	MOVW		$_rt0_arm_linux1(SB), R4
+	B		(R4)

src/pkg/runtime/signal_android_386.h

+#include "signal_linux_386.h"

src/pkg/runtime/signal_android_arm.h

+#include "signal_linux_arm.h"

src/pkg/runtime/signals_android.h

+#include "signals_linux.h"