douyou2368
2013-05-25 06:21
浏览 375
已采纳

如何使用cgo静态链接go中的c库?

So there's a bunch of stuff on the group that suggests you can do this in go (although not on the cgo documentation):

package bridge

import "fmt"

// #cgo CFLAGS: -I/Users/doug/projects/c/go-bridge/include
// #cgo LDFLAGS: /Users/doug/projects/c/go-bridge/build/libgb.a
// #include <junk.h>
import "C"

func Run() {
  fmt.Printf("Invoking c library...
")
  C.x(10)
  fmt.Printf("Done
")
}

However, it doesn't seem to work:

/var/folders/.../bridge.a(bridge.cgo2.o)(__TEXT/__text): x: not defined

This seems to work fine using a dynamic library, and inspecting the generated files, it actually has the symbol 'x' in there:

/var/folders/rg/hj4s3qlj3sz1d1b5p50ws0vc0000gn/T/go-build442792776/bridge/_obj/_cgo_.o:
0000000100001048 S _NXArgc 
0000000100001050 S _NXArgv 
0000000100001060 S ___progname 
0000000100000dc0 T __cgo_2d7eefe3d6d4_Cfunc_x
0000000100000da0 T __cgo_allocate 
0000000100000db0 T __cgo_panic
0000000100000000 T __mh_execute_header 
0000000100000d90 T _crosscall2
0000000100001058 S _environ
                 U _exit 
0000000100000d80 T _main
                 U _puts 
0000000100001000 s _pvars 
0000000100000de0 T _x                <------- Exists
                 U dyld_stub_binder 
0000000100000d40 T start

but obviously is just a marker in bridge.cgo2.o:

/var/folders/rg/hj4s3qlj3sz1d1b5p50ws0vc0000gn/T/go-build442792776/bridge.a(bridge.cgo2.o):
0000000000000368 s EH_frame0
0000000000000000 T __cgo_2d7eefe3d6d4_Cfunc_x
0000000000000380 S __cgo_2d7eefe3d6d4_Cfunc_x.eh
                 U _x

What am I doing wrong?

For ref, the c header:

int x(int y);

And code:

#include <junk.h>
#include <stdio.h>

int x(int y) {
  printf("Hello World
");
  return y;
}

--

Edit:

No, -L and -l don't work either; there's actually some specific discussion on the google group that this (-l/blah/blah.a) does not work for cgo, and the correct syntax is in fact to omit the -l and just list the .a file... but hey, if it'd worked, I'd totally just use it. But it doesn't:

dougs-mini:go doug$ go run test.go
# bridge
ld: library not found for -l/Users/doug/projects/c/go-bridge/build/libgb.a
collect2: ld returned 1 exit status
dougs-mini:go doug$ ls -l /Users/doug/projects/c/go-bridge/build/libgb.a
-rw-r--r--  1 doug  staff  872 25 May 14:02 /Users/doug/projects/c/go-bridge/build/libgb.a

verbose version:

dougs-mini:go doug$ go build -work -x test.go
WORK=/var/folders/rg/hj4s3qlj3sz1d1b5p50ws0vc0000gn/T/go-build354497708
mkdir -p $WORK/bridge/_obj/
cd /Users/doug/projects/c/go-bridge/go/src/bridge
/Users/doug/projects/go/go/pkg/tool/darwin_amd64/cgo -objdir $WORK/bridge/_obj/ -- -I/Users/doug/projects/c/go-bridge/include -I $WORK/bridge/_obj/ bridge.go
/Users/doug/projects/go/go/pkg/tool/darwin_amd64/6c -FVw -I $WORK/bridge/_obj/ -I /Users/doug/projects/go/go/pkg/darwin_amd64 -o $WORK/bridge/_obj/_cgo_defun.6 -DGOOS_darwin -DGOARCH_amd64 $WORK/bridge/_obj/_cgo_defun.c
gcc -I . -g -O2 -fPIC -m64 -pthread -fno-common -I/Users/doug/projects/c/go-bridge/include -I $WORK/bridge/_obj/ -o $WORK/bridge/_obj/_cgo_main.o -c $WORK/bridge/_obj/_cgo_main.c
gcc -I . -g -O2 -fPIC -m64 -pthread -fno-common -I/Users/doug/projects/c/go-bridge/include -I $WORK/bridge/_obj/ -o $WORK/bridge/_obj/_cgo_export.o -c $WORK/bridge/_obj/_cgo_export.c
gcc -I . -g -O2 -fPIC -m64 -pthread -fno-common -I/Users/doug/projects/c/go-bridge/include -I $WORK/bridge/_obj/ -o $WORK/bridge/_obj/bridge.cgo2.o -c $WORK/bridge/_obj/bridge.cgo2.c
gcc -I . -g -O2 -fPIC -m64 -pthread -fno-common -o $WORK/bridge/_obj/_cgo_.o $WORK/bridge/_obj/_cgo_main.o $WORK/bridge/_obj/_cgo_export.o $WORK/bridge/_obj/bridge.cgo2.o -l/Users/doug/projects/c/go-bridge/build/libgb.a
# bridge
ld: library not found for -l/Users/doug/projects/c/go-bridge/build/libgb.a
collect2: ld returned 1 exit status

It's worth noting that the failure when you try to link like this (using -l) is typical of gcc failing to link because you're attempting to combine a set of object files.

ie. This:

gcc -I . -g -O2 -fPIC -m64 -pthread -fno-common -o ... -l/path/libgb.a

Will never compile under gcc; you must link a static library like this:

gcc -I . -g -O2 -fPIC -m64 -pthread -fno-common -o ... /path/libgb.a

ie. It is absolutely not that I'm missing a -l or -L.

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4条回答 默认 最新

  • dongluni0568 2013-05-25 10:08
    已采纳

    Turns out my code is 100% fine; it was a copy of Go 1.0; under go 1.1 this works. Under go 1.0, it doesn't.

    (it's a bit lame answering my own question, I know; but the 'use -L -l answers below aren't right either; it had nothing to do with that).

    A working solution example is up on github here for anyone who find's this question later:

    https://github.com/shadowmint/go-static-linking

    in short that looks like:

    CGO_ENABLED=0 go build -a -installsuffix cgo -ldflags '-s' src/myapp/myapp.go
    

    see also: https://github.com/golang/go/issues/9344

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  • dopod0901 2013-05-25 07:51

    Try:

    // #cgo LDFLAGS: -l/Users/doug/projects/c/go-bridge/build/libgb.a
    

    You missed the -l in the LDFLAGS directive.

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  • dragonfly9527 2013-05-25 08:57

    You just have to link with -Ldirectory -lgb.

    $ cat >toto.c
    int x( int y ) { return y+1; }
    $ cat >toto.h
    int x(int);
    $ gcc -O2 -c toto.c
    $ ar q libgb.a toto.o
    $ cat >test.go
    package main
    
    import "fmt"
    
    // #cgo CFLAGS: -I.
    // #cgo LDFLAGS: -L. -lgb 
    // #include <toto.h>
    import "C"
    
    func main() {
      fmt.Printf("Invoking c library...
    ")
      fmt.Println("Done ", C.x(10) )
    }
    $ go build test.go
    $ ./test
    Invoking c library...
    Done  11
    
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  • doucheng7808 2015-04-08 18:21

    A straightforward Makefile to link Go code with a dynamic or static library:

    static:
        gcc -c gb.c
        ar -rcs libgb.a gb.o
        go build -ldflags "-linkmode external -extldflags -static" bridge.go
    
    dynamic:
        gcc -shared -o libgb.so gb.c
        go build bridge.go
    

    Directives in bridge.go:

    /*
    #cgo CFLAGS: -I.
    #cgo LDFLAGS: -L. -lgb
    #include "gb.h"
    */
    import "C"
    ...
    
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