cmd/go: support -buildmode=default,archive,exe,c-shared

Modelled somewhat on the -race support.

Change-Id: I137037addfc76341f7deb216776fdd18e9af9fe5
Reviewed-on: https://go-review.googlesource.com/8680
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/go/build.go

@@ -75,6 +75,8 @@ and test commands:
 	-x
 		print the commands.
 
+	-buildmode mode
+		build mode to use. See 'go help buildmodes' for more.
 	-compiler name
 		name of compiler to use, as in runtime.Compiler (gccgo or gc).
 	-gccgoflags 'arg list'
@@ -85,7 +87,8 @@ and test commands:
 		a suffix to use in the name of the package installation directory,
 		in order to keep output separate from default builds.
 		If using the -race flag, the install suffix is automatically set to race
-		or, if set explicitly, has _race appended to it.
+		or, if set explicitly, has _race appended to it.  Using a -buildmode
+		option that requires non-default compile flags has a similar effect.
 	-ldflags 'flag list'
 		arguments to pass on each 5l, 6l, 8l, or 9l linker invocation.
 	-asmflags 'flag list'
@@ -145,6 +148,7 @@ var buildLdflags []string    // -ldflags flag
 var buildGccgoflags []string // -gccgoflags flag
 var buildRace bool           // -race flag
 var buildToolExec []string   // -toolexec flag
+var buildBuildmode string    // -buildmode flag
 
 var buildContext = build.Default
 var buildToolchain toolchain = noToolchain{}
@@ -199,6 +203,7 @@ func addBuildFlags(cmd *Command) {
 	cmd.Flag.Var(buildCompiler{}, "compiler", "")
 	cmd.Flag.BoolVar(&buildRace, "race", false, "")
 	cmd.Flag.Var((*stringsFlag)(&buildToolExec), "toolexec", "")
+	cmd.Flag.StringVar(&buildBuildmode, "buildmode", "default", "")
 }
 
 func addBuildFlagsNX(cmd *Command) {
@@ -273,8 +278,51 @@ func (v *stringsFlag) String() string {
 	return "<stringsFlag>"
 }
 
+var pkgFilter = func(p *Package) bool { return true }
+
+func buildModeInit() {
+	var codegenArg, ldBuildmode string
+	switch buildBuildmode {
+	case "archive":
+		pkgFilter = func(p *Package) bool { return p.Name != "main" }
+	case "c-shared":
+		pkgFilter = func(p *Package) bool { return p.Name == "main" }
+		platform := goos + "/" + goarch
+		switch platform {
+		case "linux/amd64":
+		case "android/arm":
+		default:
+			fmt.Fprintf(os.Stderr, "go %s: -buildmode=c-shared not supported on %s\n", platform)
+			os.Exit(2)
+		}
+		if goarch == "amd64" {
+			codegenArg = "-shared"
+		}
+		ldBuildmode = "c-shared"
+	case "default":
+		ldBuildmode = "exe"
+	case "exe":
+		pkgFilter = func(p *Package) bool { return p.Name == "main" }
+		ldBuildmode = "exe"
+	default:
+		fatalf("buildmode=%s not supported", buildBuildmode)
+	}
+	if ldBuildmode != "" {
+		buildLdflags = append(buildLdflags, "-buildmode="+ldBuildmode)
+	}
+	if codegenArg != "" {
+		buildAsmflags = append(buildAsmflags, codegenArg)
+		buildGcflags = append(buildGcflags, codegenArg)
+		if buildContext.InstallSuffix != "" {
+			buildContext.InstallSuffix += "_"
+		}
+		buildContext.InstallSuffix += codegenArg[1:]
+	}
+}
+
 func runBuild(cmd *Command, args []string) {
 	raceInit()
+	buildModeInit()
 	var b builder
 	b.init()
 
@@ -321,7 +369,9 @@ func runBuild(cmd *Command, args []string) {
 
 	a := &action{}
 	for _, p := range packages(args) {
-		a.deps = append(a.deps, b.action(modeBuild, depMode, p))
+		if pkgFilter(p) {
+			a.deps = append(a.deps, b.action(modeBuild, depMode, p))
+		}
 	}
 	b.do(a)
 }
@@ -362,6 +412,9 @@ func runInstall(cmd *Command, args []string) {
 	a := &action{}
 	var tools []*action
 	for _, p := range pkgs {
+		if !pkgFilter(p) {
+			continue
+		}
 		// If p is a tool, delay the installation until the end of the build.
 		// This avoids installing assemblers/compilers that are being executed
 		// by other steps in the build.

src/cmd/go/doc.go

@@ -34,6 +34,7 @@ Use "go help [command]" for more information about a command.
 Additional help topics:
 
 	c           calling between Go and C
+	buildmode   description of build modes
 	filetype    file types
 	gopath      GOPATH environment variable
 	importpath  import path syntax
@@ -94,6 +95,8 @@ and test commands:
 	-x
 		print the commands.
 
+	-buildmode mode
+		build mode to use. See 'go help buildmodes' for more.
 	-compiler name
 		name of compiler to use, as in runtime.Compiler (gccgo or gc).
 	-gccgoflags 'arg list'
@@ -104,7 +107,8 @@ and test commands:
 		a suffix to use in the name of the package installation directory,
 		in order to keep output separate from default builds.
 		If using the -race flag, the install suffix is automatically set to race
-		or, if set explicitly, has _race appended to it.
+		or, if set explicitly, has _race appended to it.  Using a -buildmode
+		option that requires non-default compile flags has a similar effect.
 	-ldflags 'flag list'
 		arguments to pass on each 5l, 6l, 8l, or 9l linker invocation.
 	-asmflags 'flag list'
@@ -640,6 +644,32 @@ compiler.  The CC or CXX environment variables may be set to determine
 the C or C++ compiler, respectively, to use.
 
 
+Description of build modes
+
+The 'go build' and 'go install' commands take a -buildmode argument which
+indicates which kind of object file is to be built. Currently supported values
+are:
+
+	-buildmode=archive
+		Build the listed non-main packages into .a files. Packages named
+		main are ignored.
+
+	-buildmode=c-shared
+		Build the listed main packages, plus all packages that they
+		import, into C shared libraries. The only callable symbols will
+		be those functions marked as exported. Non-main packages are
+		ignored.
+
+	-buildmode=default
+		Listed main packages are built into executables and listed
+		non-main packages are built into .a files (the default
+		behavior).
+
+	-buildmode=exe
+		Build the listed main packages and everything they import into
+		executables. Packages not named main are ignored.
+
+
 File types
 
 The go command examines the contents of a restricted set of files

src/cmd/go/help.go

@@ -363,3 +363,32 @@ at the first item in the file that is not a blank line or //-style
 line comment.
 	`,
 }
+
+var helpBuildmode = &Command{
+	UsageLine: "buildmode",
+	Short:     "description of build modes",
+	Long: `
+The 'go build' and 'go install' commands take a -buildmode argument which
+indicates which kind of object file is to be built. Currently supported values
+are:
+
+	-buildmode=archive
+		Build the listed non-main packages into .a files. Packages named
+		main are ignored.
+
+	-buildmode=c-shared
+		Build the listed main packages, plus all packages that they
+		import, into C shared libraries. The only callable symbols will
+		be those functions marked as exported. Non-main packages are
+		ignored.
+
+	-buildmode=default
+		Listed main packages are built into executables and listed
+		non-main packages are built into .a files (the default
+		behavior).
+
+	-buildmode=exe
+		Build the listed main packages and everything they import into
+		executables. Packages not named main are ignored.
+`,
+}

src/cmd/go/main.go

@@ -91,6 +91,7 @@ var commands = []*Command{
 	cmdVet,
 
 	helpC,
+	helpBuildmode,
 	helpFileType,
 	helpGopath,
 	helpImportPath,