How do you statically link a c library in go using cgo?

Question

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...\n")   C.x(10)   fmt.Printf("Done\n") } 

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\n");   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.

Answer 1

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