尝试编译通过 JNI 从 Java 调用的 Go 共享对象时出错

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我正在尝试通过 jni 调用从 java 调用 go 函数。 java编译没问题。 当我尝试构建 go 共享对象 (.so) 时，它给出了有关可从 java 调用的 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)));
   }
}

我编译它的是：

javac locksmith.java

然后我生成了头文件：

javac -h 。锁匠.java

这是生成的文件：

/* do not edit this file - it is machine generated */
#include 
/* 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

然后我编写了 go 动态对象：

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 
#include         // 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
}

然后我编译 go 代码：

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

这会给出以下错误消息：

/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

尝试编译添加 -x 标志会导致：

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

程序版本是：

go版本go1.15.6 linux/amd64

javac 15.0.1

gcc（ubuntu 7.5.0-3ubuntu1~18.04）7.5.0

gnu ld（ubuntu 的 gnu binutils）2.30

解决方案

以下来自 cgo documentation 的内容是问题所在：

在文件中使用 //export 对前导码施加了限制：由于它被复制到两个不同的 c 输出文件中，因此它不能包含任何定义，只能包含声明。如果一个文件同时包含定义和声明，则两个输出文件将产生重复的符号，并且链接器将失败。为了避免这种情况，必须将定义放在其他文件或 c 源文件的前导码中。

移动线条

extern void setup(char *, char *, char *, char *, char *, char *);
extern char *auth(char *, char *);

到文件 locksmith.h 和 locksmith.c 的 c 定义将产生以下序言，该序言将成功构建：

/*
#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 
#include         // jni header provided by jdk
#include "locksmith.h"
#include "yada_yada_locksmith_locksmith.h"

此外，构建命令必须是

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

最后没有 locksmith.go。

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