cgo: add support for callbacks from dynamic libraries

R=golang-dev, rsc
CC=golang-dev, mpimenov
https://golang.org/cl/5375042

misc/cgo/testso/Makefile

+# Copyright 2011 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 ../../../src/Make.inc
+
+TARG=cgosotest
+
+CGO_DEPS+=libcgoso.so
+CGO_LDFLAGS+=-lcgoso -L.
+CLEANFILES+=out libcgoso.so
+CGOFILES=\
+	cgoso.go\
+
+include ../../../src/Make.pkg
+
+libcgoso.so: cgoso_c.c
+	gcc cgoso_c.c -fPIC -o $@ $(_CGO_CFLAGS_$(GOARCH)) $(_CGO_LDFLAGS_$(GOOS))
+
+out: install main.go
+	$(GC) main.go
+	$(LD) -o $@ main.$O

misc/cgo/testso/cgoso.go

+// Copyright 2011 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 cgosotest
+
+//void sofunc(void);
+import "C"
+
+func Test() {
+	C.sofunc()
+}
+
+//export goCallback
+func goCallback() {
+}

misc/cgo/testso/cgoso_c.c

+// Copyright 2011 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.
+
+void sofunc(void)
+{
+	extern void goCallback(void);
+	goCallback();
+}

misc/cgo/testso/main.go

+// Copyright 2011 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 main
+
+import "cgosotest"
+
+func main() {
+	cgosotest.Test()
+}

src/Make.pkg

@@ -162,7 +162,7 @@ endif
 # After main we have to define all the symbols that will be provided
 # by Go code.  That's crosscall2 and any exported symbols.
 
-_cgo1_.o: _cgo_main.o $(CGO_OFILES)
+_cgo1_.o: _cgo_main.o $(CGO_OFILES) $(CGO_DEPS)
 	$(HOST_CC) $(_CGO_CFLAGS_$(GOARCH)) -g -fPIC -O2 -o $@ $^ $(CGO_LDFLAGS) $(_CGO_LDFLAGS)
 
 _obj/_cgo_import.c: _cgo1_.o

src/cmd/cgo/out.go

@@ -501,6 +501,7 @@ func (p *Package) writeExports(fgo2, fc, fm *os.File) {
 		if fn.Recv != nil {
 			goname = "_cgoexpwrap" + cPrefix + "_" + fn.Recv.List[0].Names[0].Name + "_" + goname
 		}
+		fmt.Fprintf(fc, "#pragma dynexport %s %s\n", goname, goname)
 		fmt.Fprintf(fc, "extern void ·%s();\n", goname)
 		fmt.Fprintf(fc, "\nvoid\n")
 		fmt.Fprintf(fc, "_cgoexp%s_%s(void *a, int32 n)\n", cPrefix, exp.ExpName)

src/run.bash

@@ -73,6 +73,15 @@ gomake clean
 gotest
 ) || exit $?
 
+[ "$CGO_ENABLED" != 1 ] ||
+[ "$GOHOSTOS" == windows ] ||
+[ "$GOHOSTOS" == darwin ] ||
+(xcd ../misc/cgo/testso
+gomake clean
+gomake out
+LD_LIBRARY_PATH=. ./out
+) || exit $?
+
 (xcd ../doc/progs
 time ./run
 ) || exit $?