cmd/go: install headers for c-archive/c-shared cgo exports

When
  using -buildmode=c-archive or c-shared, and
  when installing packages that use cgo, and
  when those packages export some functions via //export comments,
then
  for each such package, install a pkg.h header file that declares the
  functions.

This permits C code to #include the header when calling the Go
functions.

This is a little awkward to use when there are multiple packages that
export functions, as you have to "go install" your c-archive/c-shared
object and then pull it out of the package directory.  When compiling
your C code you have to -I pkg/$GOOS_$GOARCH.  I haven't thought of
any more convenient approach.  It's simpler when only the main package
has exported functions.

When using c-shared you currently have to use a _shared suffix in the
-I option; it would be nice to fix that somehow.

Change-Id: I5d8cf08914b7d3c2b194120c77791d2732ffd26e
Reviewed-on: https://go-review.googlesource.com/9798
Reviewed-by: David Crawshaw <crawshaw@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

misc/cgo/testcarchive/main.c

@@ -5,10 +5,8 @@
 #include <stdint.h>
 #include <stdio.h>
 
-extern signed char DidInitRun();
-extern signed char DidMainRun();
-extern int32_t FromPkg();
-extern void CheckArgs();
+#include "p.h"
+#include "libgo.h"
 
 int main(void) {
 	int32_t res;

misc/cgo/testcarchive/test.bash

@@ -5,13 +5,14 @@
 
 set -e
 
-ccargs=""
+ccargs=
 if [ "$(go env GOOS)" == "darwin" ]; then
 	ccargs="-Wl,-no_pie"
 	# For darwin/arm.
 	# TODO(crawshaw): Can we do better?
 	ccargs="$ccargs -framework CoreFoundation -framework Foundation"
 fi
+ccargs="$ccargs -I pkg/$(go env GOOS)_$(go env GOARCH)"
 
 # TODO(crawshaw): Consider a go env for exec script name.
 bin=./testp
@@ -20,12 +21,24 @@ if [ "$(which $exec_script)" != "" ]; then
 	bin="$exec_script ./testp"
 fi
 
+rm -rf libgo.a libgo.h testp pkg
+
+# Installing first will create the header files we want.
+
+GOPATH=$(pwd) go install -buildmode=c-archive libgo
+$(go env CC) $(go env GOGCCFLAGS) $ccargs -o testp main.c pkg/$(go env GOOS)_$(go env GOARCH)/libgo.a
+$bin arg1 arg2
+rm -f libgo.a libgo.h testp
+
+# Test building libgo other than installing it.
+# Header files are now present.
+
 GOPATH=$(pwd) go build -buildmode=c-archive src/libgo/libgo.go
 $(go env CC) $(go env GOGCCFLAGS) $ccargs -o testp main.c libgo.a
 $bin arg1 arg2
-rm libgo.a testp
+rm -f libgo.a libgo.h testp
 
 GOPATH=$(pwd) go build -buildmode=c-archive -o libgo.a libgo
 $(go env CC) $(go env GOGCCFLAGS) $ccargs -o testp main.c libgo.a
 $bin arg1 arg2
-rm libgo.a testp
+rm -rf libgo.a libgo.h testp pkg

misc/cgo/testcshared/main0.c

@@ -5,9 +5,8 @@
 #include <stdint.h>
 #include <stdio.h>
 
-extern int8_t DidInitRun(void);
-extern int8_t DidMainRun(void);
-extern int32_t FromPkg(void);
+#include "p.h"
+#include "libgo.h"
 
 // Tests libgo.so to export the following functions.
 //   int8_t DidInitRun();

misc/cgo/testcshared/test.bash

@@ -20,7 +20,9 @@ goos=$(go env GOOS)
 androidpath=/data/local/tmp/testcshared-$$
 
 function cleanup() {
-	rm -f libgo.so libgo2.so testp testp2 testp3
+	rm -rf libgo.so libgo2.so libgo.h testp testp2 testp3 pkg
+
+	rm -rf $(go env GOROOT)/pkg/$(go env GOOS)_$(go env GOARCH)_testcshared_shared
 
 	if [ "$(go env GOOS)" == "android" ]; then
 		adb shell rm -rf $androidpath
@@ -59,11 +61,19 @@ function binpush() {
 	fi
 }
 
-GOPATH=$(pwd) go build -buildmode=c-shared -o libgo.so src/libgo/libgo.go
+rm -rf pkg
+
+suffix="-installsuffix testcshared"
+
+# Create the header files.
+GOPATH=$(pwd) go install -buildmode=c-shared $suffix libgo
+
+GOPATH=$(pwd) go build -buildmode=c-shared $suffix -o libgo.so src/libgo/libgo.go
 binpush libgo.so
 
 # test0: exported symbols in shared lib are accessible.
-$(go env CC) $(go env GOGCCFLAGS) -o testp main0.c libgo.so
+# TODO(iant): using _shared here shouldn't really be necessary.
+$(go env CC) $(go env GOGCCFLAGS) -I pkg/$(go env GOOS)_$(go env GOARCH)_testcshared_shared -o testp main0.c libgo.so
 binpush testp
 output=$(run LD_LIBRARY_PATH=. ./testp)
 if [ "$output" != "PASS" ]; then
@@ -81,7 +91,7 @@ if [ "$output" != "PASS" ]; then
 fi
 
 # test2: tests libgo2.so which does not export any functions.
-GOPATH=$(pwd) go build -buildmode=c-shared -o libgo2.so src/libgo2/libgo2.go
+GOPATH=$(pwd) go build -buildmode=c-shared $suffix -o libgo2.so src/libgo2/libgo2.go
 binpush libgo2.so
 $(go env CC) $(go env GOGCCFLAGS) -o testp2 main2.c -Wl,--no-as-needed libgo2.so
 binpush testp2

src/cmd/go/build.go

@@ -433,6 +433,11 @@ func runBuild(cmd *Command, args []string) {
 		p.target = "" // must build - not up to date
 		a := b.action(modeInstall, depMode, p)
 		a.target = *buildO
+		if p.local {
+			// If p.local, then b.action did not really install,
+			// so install the header file now if necessary.
+			a = b.maybeAddHeaderAction(a, false)
+		}
 		b.do(a)
 		return
 	}
@@ -855,6 +860,8 @@ func (b *builder) action1(mode buildMode, depMode buildMode, p *Package, looksha
 		a.f = (*builder).install
 		a.deps = []*action{b.action1(modeBuild, depMode, p, lookshared)}
 		a.target = a.p.target
+		a = b.maybeAddHeaderAction(a, true)
+
 	case modeBuild:
 		a.f = (*builder).build
 		a.target = a.objpkg
@@ -965,6 +972,49 @@ func (b *builder) libaction(libname string, pkgs []*Package, mode, depMode build
 	return a
 }
 
+// In c-archive/c-shared mode, if the package for the action uses cgo,
+// add a dependency to install the generated export header file, if
+// there is one.
+// The isInstall parameter is whether a is an install action.
+func (b *builder) maybeAddHeaderAction(a *action, isInstall bool) *action {
+	switch buildBuildmode {
+	case "c-archive", "c-shared":
+	default:
+		return a
+	}
+	if !a.p.usesCgo() {
+		return a
+	}
+
+	if isInstall {
+		// For an install action, change the action function.
+		// We can't add an action after the install action,
+		// because it deletes the working directory.
+		// Adding an action before the install action is painful,
+		// because it uses deps[0] to find the source.
+		a.f = (*builder).installWithHeader
+		return a
+	}
+
+	return &action{
+		p:      a.p,
+		deps:   []*action{a},
+		f:      (*builder).installHeader,
+		pkgdir: a.pkgdir,
+		objdir: a.objdir,
+		target: a.target[:len(a.target)-len(filepath.Ext(a.target))] + ".h",
+	}
+}
+
+// Install the library and the cgo export header if there is one.
+func (b *builder) installWithHeader(a *action) error {
+	target := a.target[:len(a.target)-len(filepath.Ext(a.target))] + ".h"
+	if err := b.doInstallHeader(a, a.objdir, target); err != nil {
+		return err
+	}
+	return b.install(a)
+}
+
 // actionList returns the list of actions in the dag rooted at root
 // as visited in a depth-first post-order traversal.
 func actionList(root *action) []*action {
@@ -1495,7 +1545,11 @@ func (b *builder) install(a *action) (err error) {
 	a1 := a.deps[0]
 	perm := os.FileMode(0644)
 	if a1.link {
-		perm = 0755
+		switch buildBuildmode {
+		case "c-archive", "c-shared":
+		default:
+			perm = 0755
+		}
 	}
 
 	// make target directory
@@ -1639,6 +1693,29 @@ func (b *builder) copyFile(a *action, dst, src string, perm os.FileMode) error {
 	return nil
 }
 
+// Install the cgo export header file, if there is one.
+func (b *builder) installHeader(a *action) error {
+	return b.doInstallHeader(a, a.objdir, a.target)
+}
+
+func (b *builder) doInstallHeader(a *action, objdir, target string) error {
+	src := objdir + "_cgo_install.h"
+	if _, err := os.Stat(src); os.IsNotExist(err) {
+		// If the file does not exist, there are no exported
+		// functions, and we do not install anything.
+		return nil
+	}
+
+	dir, _ := filepath.Split(target)
+	if dir != "" {
+		if err := b.mkdir(dir); err != nil {
+			return err
+		}
+	}
+
+	return b.moveOrCopyFile(a, target, src, 0644)
+}
+
 // cover runs, in effect,
 //	go tool cover -mode=b.coverMode -var="varName" -o dst.go src.go
 func (b *builder) cover(a *action, dst, src string, perm os.FileMode, varName string) error {
@@ -2742,7 +2819,16 @@ func (b *builder) cgo(p *Package, cgoExe, obj string, pcCFLAGS, pcLDFLAGS, cgofi
 			cgoflags = append(cgoflags, "-gccgopkgpath="+pkgpath)
 		}
 	}
-	if err := b.run(p.Dir, p.ImportPath, cgoenv, buildToolExec, cgoExe, "-objdir", obj, cgoflags, "--", cgoCPPFLAGS, cgoexeCFLAGS, cgofiles); err != nil {
+
+	switch buildBuildmode {
+	case "c-archive", "c-shared":
+		// Tell cgo that if there are any exported functions
+		// it should generate a header file that C code can
+		// #include.
+		cgoflags = append(cgoflags, "-exportheader="+obj+"_cgo_install.h")
+	}
+
+	if err := b.run(p.Dir, p.ImportPath, cgoenv, buildToolExec, cgoExe, "-objdir", obj, "-importpath", p.ImportPath, cgoflags, "--", cgoCPPFLAGS, cgoexeCFLAGS, cgofiles); err != nil {
 		return nil, nil, err
 	}
 	outGo = append(outGo, gofiles...)

src/cmd/go/pkg.go

@@ -487,7 +487,15 @@ func (p *Package) load(stk *importStack, bp *build.Package, err error) *Package
 		return p
 	}
 
-	if p.Name == "main" {
+	useBindir := p.Name == "main"
+	if !p.Standard {
+		switch buildBuildmode {
+		case "c-archive", "c-shared":
+			useBindir = false
+		}
+	}
+
+	if useBindir {
 		// Report an error when the old code.google.com/p/go.tools paths are used.
 		if goTools[p.ImportPath] == stalePath {
 			newPath := strings.Replace(p.ImportPath, "code.google.com/p/go.", "golang.org/x/", 1)