近期在某本书上看到Go跨平台交叉编译的强大功能,于是想自己测试一下。以下记录了测试过程以及一些结论,希望能给大家带来帮助。

我的Linux环境如下:

uname -a
Linux ubuntu-Server-14 3.13.0-32-generic #57-Ubuntu SMP Tue Jul 15 03:51:08 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux

$ go version
go version go1.3.1 linux/amd64

跨平台交叉编译涉及两个重要的环境变量:GOOS和GOARCH,分别代表Target Host OS和Target Host ARCH,如果没有显式设置这些环境变量,我们通过go env可以看到go编译器眼中这两个环境变量的当前值:

$ go env
GOARCH="amd64"
GOOS="linux"

GOHOSTARCH="amd64"
GOHOSTOS="linux"

… …

这里还有两个变量GOHOSTOS和GOHOSTARCH,分别表示的是当前所在主机的的OS和CPU ARCH。我的Go是采用安装包安装的,因此默认情况下,这两组环境变量的值都是来自当前主机的信息。

现在我们就来交叉编译一下:在linux/amd64平台下利用Go编译器编译一个可以运行在linux/amd64下的程序,样例程序如下:

//testport.go
package main

import (
        "fmt"
        "os/exec"
        "bytes"
)

func main() {
        cmd := exec.Command("uname", "-a")
        var out bytes.Buffer
        cmd.Stdout = &out

        err := cmd.Run()
        if err != nil {
                fmt.Println("Err when executing uname command")
                return
        }

        fmt.Println("I am running on", out.String())
}

在Linux/amd64下编译运行:

$ go build -o testport_linux testport.go
$ testport_linux
I am running on Linux ubuntu-Server-14 3.13.0-32-generic #57-Ubuntu SMP Tue Jul 15 03:51:08 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux

接下来,我们来尝试在Linux/amd64上编译一个可以运行在darwin/amd64上的程序。我只需修改GOOS和GOARCH两个标识目标主机OS和ARCH的环境变量:

$ GOOS=darwin GOARCH=amd64 go build -o testport_darwin testport.go
go build runtime: darwin/amd64 must be bootstrapped using make.bash

编译器报错了!提示darwin/amd64必须通过make.bash重新装载。显然,通过安装包安装到linux/amd64下的Go编译器还无法直接交叉编译出darwin/amd64下可以运行的程序,我们需要做一些准备工作。我们找找make.bash在哪里!

我们到Go的$GOROOT路径下去找make.bash,Go的安装路径下的组织很简约,扫一眼便知make.sh大概在$GOROOT/src下,打开make.sh,我们在文件头处看到如下一些内容:

# Environment variables that control make.bash:
#
# GOROOT_FINAL: The expected final Go root, baked into binaries.
# The default is the location of the Go tree during the build.
#
# GOHOSTARCH: The architecture for host tools (compilers and
# binaries).  Binaries of this type must be executable on the current
# system, so the only common reason to set this is to set
# GOHOSTARCH=386 on an amd64 machine.
#
# GOARCH: The target architecture for installed packages and tools.
#
# GOOS: The target operating system for installed packages and tools.

… …

make.bash头并未简要说明文件的用途,但名为make.xx的文件想必是用来构建Go编译工具的。这里提到几个环境变量可以控制 make.bash的行为,显然GOARCH和GOOS更能引起我们的兴趣。我们再回过头来输出testport.go编译过程的详细信息:

$ go build -x -o testport_linux testport.go
WORK=/tmp/go-build286732099
mkdir -p $WORK/command-line-arguments/_obj/
cd /home/tonybai/Test/Go/porting
/usr/local/go/pkg/tool/linux_amd64/6g -o $WORK/command-line-arguments.a -trimpath $WORK -p command-line-arguments -complete -D _/home/tonybai/Test/Go/porting -I $WORK -pack ./testport.go
cd .
/usr/local/go/pkg/tool/linux_amd64/6l -o testport_linux -L $WORK -extld=gcc $WORK/command-line-arguments.a

我们发现Go实际上用的是$GOROOT/pkg/tool/linux_amd64下的6g(编译器)和6l(链接器)来完成整个编译过程的,看到6g 和6l所在目录名为linux_amd64,我们可以大胆猜测编译darwin/amd64 go程序应该使用的是$GOROOT/pkg/tool/darwin_amd64下的工具。不过在我在$GOROOT/pkg/tool下没有发现 darwin_amd64目录,也就是说我们通过安装包安装的Go仅自带了for linux_amd64的编译工具,要想交叉编译出for darwin_amd64的程序,我们需要通过make.bash来手工编译出这些工具。

tonybai@ubuntu-Server-14:/usr/local/go/pkg$ ls
linux_amd64  linux_amd64_race  obj  tool

tonybai@ubuntu-Server-14:/usr/local/go/pkg/tool$ ls
linux_amd64

根据前面make.bash的用法说明,我们来尝试构建一下:

cd $GOROOT/src
sudo GOOS=darwin GOARCH=amd64 ./make.bash

# Building C bootstrap tool.
cmd/dist

# Building compilers and Go bootstrap tool for host, linux/amd64.
… …
cmd/cc
cmd/gc
cmd/6l
cmd/6a
cmd/6c
cmd/6g
pkg/runtime
… …
cmd/go
pkg/runtime (darwin/amd64)

# Building packages and commands for host, linux/amd64.
runtime
… …
text/scanner

# Building packages and commands for darwin/amd64.
runtime
errors
… …
testing/quick
text/scanner


Installed Go for darwin/amd64 in /usr/local/go
Installed commands in /usr/local/go/bin

编译后,我们再来试试编译for darwin_amd64的程序:

$ GOOS=darwin GOARCH=amd64 go build -x -o testport_darwin testport.go
WORK=/tmp/go-build972764136
mkdir -p $WORK/command-line-arguments/_obj/
cd /home/tonybai/Test/Go/porting
/usr/local/go/pkg/tool/linux_amd64/6g -o $WORK/command-line-arguments.a -trimpath $WORK -p command-line-arguments -complete -D _/home/tonybai/Test/Go/porting -I $WORK -pack ./testport.go
cd .
/usr/local/go/pkg/tool/linux_amd64/6l -o testport_darwin -L $WORK -extld=gcc $WORK/command-line-arguments.a

将文件copy到我的Mac Air下执行:

$chmod +x testport_darwin
$testport_darwin
I am running on Darwin TonydeMacBook-Air.local 13.1.0 Darwin Kernel Version 13.1.0: Thu Jan 16 19:40:37 PST 2014; root:xnu-2422.90.20~2/RELEASE_X86_64 x86_64

编译虽然成功了,但从-x输出的详细编译过程来看,Go编译连接使用的工具依旧是linux_amd64下的6g和6l,为什么没有使用darwin_amd64下的6g和6l呢?原来$GOROOT/pkg/tool/darwin_amd64下根本就没有6g和6l:

/usr/local/go/pkg/tool/darwin_amd64$ ls
addr2line  cgo  fix  nm  objdump  pack  yac
c

但查看一下pkg/tool/linux_amd64/下程序的更新时间:

/usr/local/go/pkg/tool/linux_amd64$ ls -l
… …
-rwxr-xr-x 1 root root 2482877 10月 20 15:12 6g
-rwxr-xr-x 1 root root 1186445 10月 20 15:12 6l
… …

我们发现6g和6l都是被刚才的make.bash新编译出来的,我们可以得出结论:新6g和新6l目前既可以编译本地程序(linux/amd64),也可以编译darwin/amd64下的程序了,例如重新编译testport_linux依旧ok:

$ go build -x -o testport_linux testport.go
WORK=/tmp/go-build636762567
mkdir -p $WORK/command-line-arguments/_obj/
cd /home/tonybai/Test/Go/porting
/usr/local/go/pkg/tool/linux_amd64/6g -o $WORK/command-line-arguments.a -trimpath $WORK -p command-line-arguments -complete -D _/home/tonybai/Test/Go/porting -I $WORK -pack ./testport.go
cd .
/usr/local/go/pkg/tool/linux_amd64/6l -o testport_linux -L $WORK -extld=gcc $WORK/command-line-arguments.a

如果我们还想给Go编译器加上交叉编译windows/amd64程序的功能,我们再执行一次make.bash:

sudo GOOS=windows GOARCH=amd64 ./make.bash

编译成功后,我们来编译一下Windows程序:

$ GOOS=windows GOARCH=amd64 go build -x -o testport_windows.exe testport.go
WORK=/tmp/go-build626615350
mkdir -p $WORK/command-line-arguments/_obj/
cd /home/tonybai/Test/Go/porting
/usr/local/go/pkg/tool/linux_amd64/6g -o $WORK/command-line-arguments.a -trimpath $WORK -p command-line-arguments -complete -D _/home/tonybai/Test/Go/porting -I $WORK -pack ./testport.go
cd .
/usr/local/go/pkg/tool/linux_amd64/6l -o testport_windows.exe -L $WORK -extld=gcc $WORK/command-line-arguments.a

把testport_windows.exe扔到Windows上执行,结果:

Err when executing uname command

显然Windows下没有uname命令,提示执行出错。

至此,我的Go编译器具备了在Linux下编译windows/amd64和darwin/amd64的能力。如果你还想增加其他平台的能力,就像上面那样操作执行make.bash即可。

如果在go源文件中有与C语言的交互代码,那么交叉编译功能是否还能奏效呢?毕竟C在各个平台上的运行库、链接库等都是不同的。我们先来看看这个例子,我们使用之前在《探讨docker容器对共享内存的支持情况》一文中的一个例子:

//testport_cgoenabled.go
package main

//#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/tonybai/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/tonybai/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/tonybai/Test/Go/porting

当我们编译for Darwin/amd64平台的程序时,Go无法像之前那样的顺利完成编译,而是提示错误。从网上给出的资料来看,如果Go源码中包含C互操作代码,那么 目前依旧无法实现交叉编译,因为cgo会直接使用各个平台的本地c编译器去编译Go文件中的C代码。默认情况下,make.bash会置 CGO_ENABLED=0。

如果你非要将CGO_ENABLED设置为1去编译go的话,至少我得到了如下错误,导致无法编译通过:

$ sudo CGO_ENABLED=1 GOOS=darwin GOARCH=amd64 ./make.bash –no-clean
… …
# Building packages and commands for darwin/amd64.
… …
37: error: 'AI_MASK' undeclared (first use in this function)

 

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