编译Go共享对象以通过JNI从Java调用时出错

Question

我试图通过JNI调用从Java调用Go函数。Java编译也可以。当我试图构建Go共享对象(Go shared object，.so)时，它会给出关于C函数包装器的“多个定义”的错误。

这是Java代码：

package yada.yada.locksmith;

import java.io.*;

public class Locksmith {

   private native void setup(String ClientID, String ClientSecret, String RedirectURL, String AuthURL, String TokenURL, String UserInfURL);
   private native String auth(String user, String pw);

   static {
      System.loadLibrary("Locksmith");
   }

   public static void Locksmith(String[] args) {
      Locksmith locksmith = new Locksmith();

      locksmith.setup(
         "yadayadayadayadayadayadayadayadayadayada",
         "yadayadayadayadayadayadayadayadayadayada",
         "https://yada.yada/Yada/yada",
         "https://yada.yada/Yada/yada2",
         "https://yada.yada/Yada/yada3",
         "https://yada.yada/Yada/yada4"
      );

      // Create the console object
      Console cnsl = System.console();

      if (cnsl == null) {
         System.out.println("No console available");
         return;
      }

      String user = cnsl.readLine("Enter username : ");
      char[] pw = cnsl.readPassword("Enter password : ");
      System.out.println(locksmith.auth(user,new String(pw)));
   }
}

我是用以下方式编写的：

javac Locksmith.java

然后，我用以下内容生成了头文件：

javac -h .Locksmith.java

这是生成的文件：

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class yada_yada_locksmith_Locksmith */

#ifndef _Included_yada_yada_locksmith_Locksmith
#define _Included_yada_yada_locksmith_Locksmith
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     yada_yada_locksmith_Locksmith
 * Method:    setup
 * Signature: (Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;)V
 */
JNIEXPORT void JNICALL Java_yada_yada_locksmith_Locksmith_setup
  (JNIEnv *, jobject, jstring, jstring, jstring, jstring, jstring, jstring);

/*
 * Class:     yada_yada_locksmith_Locksmith
 * Method:    auth
 * Signature: (Ljava/lang/String;Ljava/lang/String;)Ljava/lang/String;
 */
JNIEXPORT jstring JNICALL Java_yada_yada_locksmith_Locksmith_auth
  (JNIEnv *, jobject, jstring, jstring);

#ifdef __cplusplus
}
#endif
#endif

然后我对Go动态对象进行了编码：

package main

import (
//   "io"
//   "fmt"
   "log"
   "sync"
   "net/url"
   "strings"
   "context"
   "net/http"
   "io/ioutil"
   "golang.org/x/oauth2"
   "github.com/chromedp/chromedp"
   "github.com/chromedp/cdproto/network"
)

/*
#cgo CFLAGS: -I/usr/local/bin/jdk-15.0.1/include -I/usr/local/bin/jdk-15.0.1/include/linux

#include <string.h>
#include <jni.h>        // JNI header provided by JDK
#include "yada_yada_locksmith_Locksmith.h"

extern void Setup(char *, char *, char *, char *, char *, char *);
extern char *Auth(char *, char *);

JNIEXPORT void JNICALL Java_yada_yada_locksmith_Locksmith_setup
  (JNIEnv *env, jobject this, jstring ClientID, jstring ClientSecret, jstring RedirectURL, jstring AuthURL, jstring TokenURL, jstring UserInfURL) {

   char *CClientID;
   char *CClientSecret;
   char *CRedirectURL;
   char *CAuthURL;
   char *CTokenURL;
   char *CUserInfURL;

   CClientID = ((char *)(*env)->GetStringUTFChars(env, ClientID, 0));
   CClientSecret = ((char *)(*env)->GetStringUTFChars(env, ClientSecret, 0));
   CRedirectURL = ((char *)(*env)->GetStringUTFChars(env, RedirectURL, 0));
   CAuthURL = ((char *)(*env)->GetStringUTFChars(env, AuthURL, 0));
   CTokenURL = ((char *)(*env)->GetStringUTFChars(env, TokenURL, 0));
   CUserInfURL = ((char *)(*env)->GetStringUTFChars(env, UserInfURL, 0));

   Setup(CClientID, CClientSecret, CRedirectURL, CAuthURL, CTokenURL, CUserInfURL);

   (*env)->ReleaseStringUTFChars(env, ClientID, CClientID);
   (*env)->ReleaseStringUTFChars(env, ClientSecret, CClientSecret);
   (*env)->ReleaseStringUTFChars(env, RedirectURL, CRedirectURL);
   (*env)->ReleaseStringUTFChars(env, AuthURL, CAuthURL);
   (*env)->ReleaseStringUTFChars(env, TokenURL, CTokenURL);
   (*env)->ReleaseStringUTFChars(env, UserInfURL, CUserInfURL);
}

JNIEXPORT jstring JNICALL Java_yada_yada_locksmith_Locksmith_auth
  (JNIEnv *env, jobject this, jstring User, jstring Pw) {

   char *CUser;
   char *CPw;

   CUser = ((char *)(*env)->GetStringUTFChars(env, User, 0));
   CPw = ((char *)(*env)->GetStringUTFChars(env, Pw, 0));


   // Call
   Auth(CUser, CPw);

   (*env)->ReleaseStringUTFChars(env, User, CUser);
   (*env)->ReleaseStringUTFChars(env, Pw, CPw);
}


*/
import "C"

type oauthConfT struct {
   Cfg *oauth2.Config
   UserInfURL string
}

func main() {
}

var cfg oauthConfT

//export Setup
func Setup(ClientID, ClientSecret, RedirectURL, AuthURL, TokenURL, UserInfURL *C.char) {
   // DO stuff
}

//export Auth
func Auth(user, pw *C.char) *C.char {
   // DO stuff
}

然后，我用以下方法编译Go代码：

go build -o liblocksmith.so -buildmode=c共享locksmith.go

这提供了折叠错误消息：

/tmp/go-build051144078/b001/_x002.o: In function "Java_yada_yada_locksmith_Locksmith_setup":
./locksmith.go:29: multiple definition in "Java_yada_yada_locksmith_Locksmith_setup"
/tmp/go-build051144078/b001/_x001.o:/tmp/go-build/locksmith.go:29: defined first here
/tmp/go-build051144078/b001/_x002.o: In function "Java_yada_yada_locksmith_Locksmith_auth":
./locksmith.go:56: multiple definition in "Java_yada_yada_locksmith_Locksmith_auth"
/tmp/go-build051144078/b001/_x001.o:/tmp/go-build/locksmith.go:56: defined first here
collect2: error: ld returned 1 exit status

试图编译添加-x标志将导致以下结果：

WORK=/tmp/go-build051144078
mkdir -p $WORK/b056/
cd /home/vuco/repos/go/src/runtime/cgo
CGO_LDFLAGS='"-g" "-O2" "-lpthread"' /home/vuco/repos/go/pkg/tool/linux_amd64/cgo -objdir $WORK/b056/ -importpath runtime/cgo -import_runtime_cgo=false -import_syscall=false -exportheader=$WORK/b056/_cgo_install.h -- -I $WORK/b056/ -g -O2 -Wall -Werror ./cgo.go
cd $WORK
gcc -fno-caret-diagnostics -c -x c - -o /dev/null || true
gcc -Qunused-arguments -c -x c - -o /dev/null || true
gcc -fdebug-prefix-map=a=b -c -x c - -o /dev/null || true
gcc -gno-record-gcc-switches -c -x c - -o /dev/null || true
cd $WORK/b056
TERM='dumb' gcc -I /home/vuco/repos/go/src/runtime/cgo -fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=$WORK/b056=/tmp/go-build -gno-record-gcc-switches -I ./ -g -O2 -Wall -Werror -o ./_x001.o -c _cgo_export.c
TERM='dumb' gcc -I /home/vuco/repos/go/src/runtime/cgo -fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=$WORK/b056=/tmp/go-build -gno-record-gcc-switches -I ./ -g -O2 -Wall -Werror -o ./_x002.o -c cgo.cgo2.c
cd /home/vuco/repos/go/src/runtime/cgo
TERM='dumb' gcc -I . -fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=$WORK/b056=/tmp/go-build -gno-record-gcc-switches -I $WORK/b056/ -g -O2 -Wall -Werror -o $WORK/b056/_x003.o -c gcc_context.c
TERM='dumb' gcc -I . -fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=$WORK/b056=/tmp/go-build -gno-record-gcc-switches -I $WORK/b056/ -g -O2 -Wall -Werror -o $WORK/b056/_x004.o -c gcc_fatalf.c
TERM='dumb' gcc -I . -fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=$WORK/b056=/tmp/go-build -gno-record-gcc-switches -I $WORK/b056/ -g -O2 -Wall -Werror -o $WORK/b056/_x005.o -c gcc_libinit.c
TERM='dumb' gcc -I . -fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=$WORK/b056=/tmp/go-build -gno-record-gcc-switches -I $WORK/b056/ -g -O2 -Wall -Werror -o $WORK/b056/_x006.o -c gcc_linux_amd64.c
TERM='dumb' gcc -I . -fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=$WORK/b056=/tmp/go-build -gno-record-gcc-switches -I $WORK/b056/ -g -O2 -Wall -Werror -o $WORK/b056/_x007.o -c gcc_mmap.c
TERM='dumb' gcc -I . -fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=$WORK/b056=/tmp/go-build -gno-record-gcc-switches -I $WORK/b056/ -g -O2 -Wall -Werror -o $WORK/b056/_x008.o -c gcc_setenv.c
TERM='dumb' gcc -I . -fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=$WORK/b056=/tmp/go-build -gno-record-gcc-switches -I $WORK/b056/ -g -O2 -Wall -Werror -o $WORK/b056/_x009.o -c gcc_sigaction.c
TERM='dumb' gcc -I . -fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=$WORK/b056=/tmp/go-build -gno-record-gcc-switches -I $WORK/b056/ -g -O2 -Wall -Werror -o $WORK/b056/_x010.o -c gcc_traceback.c
TERM='dumb' gcc -I . -fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=$WORK/b056=/tmp/go-build -gno-record-gcc-switches -I $WORK/b056/ -g -O2 -Wall -Werror -o $WORK/b056/_x011.o -c gcc_util.c
TERM='dumb' gcc -I . -fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=$WORK/b056=/tmp/go-build -gno-record-gcc-switches -I $WORK/b056/ -g -O2 -Wall -Werror -o $WORK/b056/_x012.o -c gcc_amd64.S
cd $WORK/b056
TERM='dumb' gcc -I /home/vuco/repos/go/src/runtime/cgo -fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=$WORK/b056=/tmp/go-build -gno-record-gcc-switches -I ./ -g -O2 -Wall -Werror -o ./_cgo_main.o -c _cgo_main.c
cd /home/vuco/repos/go/src/runtime/cgo
TERM='dumb' gcc -I . -fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=$WORK/b056=/tmp/go-build -gno-record-gcc-switches -o $WORK/b056/_cgo_.o $WORK/b056/_cgo_main.o $WORK/b056/_x001.o $WORK/b056/_x002.o $WORK/b056/_x003.o $WORK/b056/_x004.o $WORK/b056/_x005.o $WORK/b056/_x006.o $WORK/b056/_x007.o $WORK/b056/_x008.o $WORK/b056/_x009.o $WORK/b056/_x010.o $WORK/b056/_x011.o $WORK/b056/_x012.o -g -O2 -lpthread
TERM='dumb' /home/vuco/repos/go/pkg/tool/linux_amd64/cgo -dynpackage cgo -dynimport $WORK/b056/_cgo_.o -dynout $WORK/b056/_cgo_import.go -dynlinker
mkdir -p $WORK/b051/
cd /home/vuco/repos/go/src/net
CGO_LDFLAGS='"-g" "-O2"' /home/vuco/repos/go/pkg/tool/linux_amd64/cgo -objdir $WORK/b051/ -importpath net -exportheader=$WORK/b051/_cgo_install.h -- -I $WORK/b051/ -g -O2 ./cgo_linux.go ./cgo_resnew.go ./cgo_socknew.go ./cgo_unix.go
cd $WORK/b051
TERM='dumb' gcc -I /home/vuco/repos/go/src/net -fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=$WORK/b051=/tmp/go-build -gno-record-gcc-switches -I ./ -g -O2 -o ./_x001.o -c _cgo_export.c
TERM='dumb' gcc -I /home/vuco/repos/go/src/net -fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=$WORK/b051=/tmp/go-build -gno-record-gcc-switches -I ./ -g -O2 -o ./_x002.o -c cgo_linux.cgo2.c
TERM='dumb' gcc -I /home/vuco/repos/go/src/net -fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=$WORK/b051=/tmp/go-build -gno-record-gcc-switches -I ./ -g -O2 -o ./_x003.o -c cgo_resnew.cgo2.c
TERM='dumb' gcc -I /home/vuco/repos/go/src/net -fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=$WORK/b051=/tmp/go-build -gno-record-gcc-switches -I ./ -g -O2 -o ./_x004.o -c cgo_socknew.cgo2.c
TERM='dumb' gcc -I /home/vuco/repos/go/src/net -fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=$WORK/b051=/tmp/go-build -gno-record-gcc-switches -I ./ -g -O2 -o ./_x005.o -c cgo_unix.cgo2.c
TERM='dumb' gcc -I /home/vuco/repos/go/src/net -fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=$WORK/b051=/tmp/go-build -gno-record-gcc-switches -I ./ -g -O2 -o ./_cgo_main.o -c _cgo_main.c
cd /home/vuco/repos/go/src/net
TERM='dumb' gcc -I . -fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=$WORK/b051=/tmp/go-build -gno-record-gcc-switches -o $WORK/b051/_cgo_.o $WORK/b051/_cgo_main.o $WORK/b051/_x001.o $WORK/b051/_x002.o $WORK/b051/_x003.o $WORK/b051/_x004.o $WORK/b051/_x005.o -g -O2
TERM='dumb' /home/vuco/repos/go/pkg/tool/linux_amd64/cgo -dynpackage net -dynimport $WORK/b051/_cgo_.o -dynout $WORK/b051/_cgo_import.go
mkdir -p $WORK/b001/
cd /home/vuco/repos/yada/src/main/java/yada/yada/locksmith
CGO_LDFLAGS='"-g" "-O2"' /home/vuco/repos/go/pkg/tool/linux_amd64/cgo -objdir $WORK/b001/ -importpath command-line-arguments -exportheader=$WORK/b001/_cgo_install.h -- -I $WORK/b001/ -g -O2 -I/usr/local/bin/jdk-15.0.1/include -I/usr/local/bin/jdk-15.0.1/include/linux ./locksmith.go
cd $WORK/b001
TERM='dumb' gcc -I /home/vuco/repos/yada/src/main/java/yada/yada/locksmith -fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=$WORK/b001=/tmp/go-build -gno-record-gcc-switches -I ./ -g -O2 -I/usr/local/bin/jdk-15.0.1/include -I/usr/local/bin/jdk-15.0.1/include/linux -o ./_x001.o -c _cgo_export.c
TERM='dumb' gcc -I /home/vuco/repos/yada/src/main/java/yada/yada/locksmith -fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=$WORK/b001=/tmp/go-build -gno-record-gcc-switches -I ./ -g -O2 -I/usr/local/bin/jdk-15.0.1/include -I/usr/local/bin/jdk-15.0.1/include/linux -o ./_x002.o -c locksmith.cgo2.c
TERM='dumb' gcc -I /home/vuco/repos/yada/src/main/java/yada/yada/locksmith -fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=$WORK/b001=/tmp/go-build -gno-record-gcc-switches -I ./ -g -O2 -I/usr/local/bin/jdk-15.0.1/include -I/usr/local/bin/jdk-15.0.1/include/linux -o ./_cgo_main.o -c _cgo_main.c
cd /home/vuco/repos/yada/src/main/java/yada/yada/locksmith
TERM='dumb' gcc -I . -fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=$WORK/b001=/tmp/go-build -gno-record-gcc-switches -o $WORK/b001/_cgo_.o $WORK/b001/_cgo_main.o $WORK/b001/_x001.o $WORK/b001/_x002.o -g -O2
# command-line-arguments
/tmp/go-build051144078/b001/_x002.o: In function "Java_yada_yada_locksmith_Locksmith_setup":
./locksmith.go:29: multiple definition in "Java_yada_yada_locksmith_Locksmith_setup"
/tmp/go-build051144078/b001/_x001.o:/tmp/go-build/locksmith.go:29: defined first here
/tmp/go-build051144078/b001/_x002.o: In function "Java_yada_yada_locksmith_Locksmith_auth":
./locksmith.go:56: multiple definition in "Java_yada_yada_locksmith_Locksmith_auth"
/tmp/go-build051144078/b001/_x001.o:/tmp/go-build/locksmith.go:56: defined first here
collect2: error: ld returned 1 exit status

程序版本如下：

go版本go1.15.6 linux/amd64 64

javac 15.0.1

gcc (Ubuntu 7.5.0-3 ubuntu1~18.04) 7.5.0

GNU ld (Ubuntu的GNU Binutils )

Answer 1

来自cgo文档的以下是问题所在：

在文件中使用//export对序言有一个限制:由于它被复制到两个不同的C输出文件中，所以它不能包含任何定义，只包含声明。如果一个文件同时包含定义和声明，那么这两个输出文件将产生重复的符号，链接器将失败。为了避免这种情况，定义必须放在其他文件中的序言中，或者放在C源文件中。

移动线

extern void Setup(char *, char *, char *, char *, char *, char *);
extern char *Auth(char *, char *);

对于文件locksmith.h和locksmith.c的C定义将产生以下序言，它成功构建：

/*
#cgo CFLAGS: -I/usr/local/bin/jdk-15.0.1/include -I/usr/local/bin/jdk-15.0.1/include/linux

#include "locksmith.h"
*/
import "C"

locksmith.c的开头将包含以下内容：

#include <string.h>
#include <jni.h>        // JNI header provided by JDK
#include "locksmith.h"
#include "yada_yada_locksmith_Locksmith.h"

此外，构建命令需要是

go build -o liblocksmith.so -buildmode=c-shared

在结束时没有locksmith.go。