//#include <stdio.h>
//#include <sys/types.h>
//#include <sys/mman.h>
//#include <fcntl.h>
//
//#define SHMSZ 27
//
//int shm_rd()
//{
// char c;
// char *shm = NULL;
// char *s = NULL;
// int fd;
// if ((fd = open("./shm.txt", O_RDONLY)) == -1) {
// return -1;
// }
//
// shm = (char*)mmap(shm, SHMSZ, PROT_READ, MAP_SHARED, fd, 0);
// if (!shm) {
// return -2;
// }
//
// close(fd);
// s = shm;
// int i = 0;
// for (i = 0; i < SHMSZ – 1; i++) {
// printf("%c ", *(s + i));
// }
// printf("\n");
//
// return 0;
//}
import "C"
import "fmt"
func main() {
i := C.shm_rd()
if i != 0 {
fmt.Println("Mmap Share Memory Read Error:", i)
return
}
fmt.Println("Mmap Share Memory Read Ok")
}
我们先编译出一个本地可运行的程序：
$ go build -x -o testport_cgoenabled_linux testport_cgoenabled.go
WORK=/tmp/go-build977176241
mkdir -p $WORK/command-line-arguments/_obj/
cd /home/linuxidc/Test/Go/porting
CGO_LDFLAGS="-g" "-O2" /usr/local/go/pkg/tool/linux_amd64/cgo -objdir $WORK/command-line-arguments/_obj/ — -I $WORK/command-line-arguments/_obj/ testport_cgoenabled.go
/usr/local/go/pkg/tool/linux_amd64/6c -F -V -w -trimpath $WORK -I $WORK/command-line-arguments/_obj/ -I /usr/local/go/pkg/linux_amd64 -o $WORK/command-line-arguments/_obj/_cgo_defun.6 -D GOOS_linux -D GOARCH_amd64 $WORK/command-line-arguments/_obj/_cgo_defun.c
gcc -I . -fPIC -m64 -pthread -fmessage-length=0 -print-libgcc-file-name
gcc -I . -fPIC -m64 -pthread -fmessage-length=0 -I $WORK/command-line-arguments/_obj/ -g -O2 -o $WORK/command-line-arguments/_obj/_cgo_main.o -c $WORK/command-line-arguments/_obj/_cgo_main.c
gcc -I . -fPIC -m64 -pthread -fmessage-length=0 -I $WORK/command-line-arguments/_obj/ -g -O2 -o $WORK/command-line-arguments/_obj/_cgo_export.o -c $WORK/command-line-arguments/_obj/_cgo_export.c
gcc -I . -fPIC -m64 -pthread -fmessage-length=0 -I $WORK/command-line-arguments/_obj/ -g -O2 -o $WORK/command-line-arguments/_obj/testport_cgoenabled.cgo2.o -c $WORK/command-line-arguments/_obj/testport_cgoenabled.cgo2.c
gcc -I . -fPIC -m64 -pthread -fmessage-length=0 -o $WORK/command-line-arguments/_obj/_cgo_.o $WORK/command-line-arguments/_obj/_cgo_main.o $WORK/command-line-arguments/_obj/_cgo_export.o $WORK/command-line-arguments/_obj/testport_cgoenabled.cgo2.o -g -O2
/usr/local/go/pkg/tool/linux_amd64/cgo -objdir $WORK/command-line-arguments/_obj/ -dynimport $WORK/command-line-arguments/_obj/_cgo_.o -dynout $WORK/command-line-arguments/_obj/_cgo_import.c
/usr/local/go/pkg/tool/linux_amd64/6c -F -V -w -trimpath $WORK -I $WORK/command-line-arguments/_obj/ -I /usr/local/go/pkg/linux_amd64 -o $WORK/command-line-arguments/_obj/_cgo_import.6 -D GOOS_linux -D GOARCH_amd64 $WORK/command-line-arguments/_obj/_cgo_import.c
gcc -I . -fPIC -m64 -pthread -fmessage-length=0 -o $WORK/command-line-arguments/_obj/_all.o $WORK/command-line-arguments/_obj/_cgo_export.o $WORK/command-line-arguments/_obj/testport_cgoenabled.cgo2.o -g -O2 -Wl,-r -nostdlib /usr/lib/gcc/x86_64-linux-gnu/4.8/libgcc.a
/usr/local/go/pkg/tool/linux_amd64/6g -o $WORK/command-line-arguments.a -trimpath $WORK -p command-line-arguments -D _/home/linuxidc/Test/Go/porting -I $WORK -pack $WORK/command-line-arguments/_obj/_cgo_gotypes.go $WORK/command-line-arguments/_obj/testport_cgoenabled.cgo1.go
pack r $WORK/command-line-arguments.a $WORK/command-line-arguments/_obj/_cgo_import.6 $WORK/command-line-arguments/_obj/_cgo_defun.6 $WORK/command-line-arguments/_obj/_all.o # internal
cd .
/usr/local/go/pkg/tool/linux_amd64/6l -o testport_cgoenabled_linux -L $WORK -extld=gcc $WORK/command-line-arguments.a
输出了好多日志！不过可以看出Go编译器先调用CGO对Go源码中的C代码进行了编译，然后才是常规的Go编译，最后通过6l链接在一起。Cgo似乎直接使用了Gcc。我们再来试试跨平台编译：
$ GOOS=darwin GOARCH=amd64 go build -x -o testport_cgoenabled_darwin testport_cgoenabled.go
WORK=/tmp/go-build124869433
can't load package: no buildable Go source files in /home/linuxidc/Test/Go/porting