How do you statically link a c library in go using cgo?
Solution 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
Solution 2
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...\n")
fmt.Println("Done ", C.x(10) )
}
$ go build test.go
$ ./test
Invoking c library...
Done 11
Solution 3
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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Doug
Updated on July 27, 2020Comments
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Doug almost 4 years
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.
-
Intermernet about 11 yearsAre you missing a
-L
afterLDFLAGS:
?
-
-
Intermernet about 11 yearsDamn, was hoping it was just a typo, other than that I can't see why it wouldn't be working
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fuz about 11 yearsWasn't it that you need both -L/Users/doug/projects/c/go-bridge/build/ and -lgb ? (the first belongs to LDFLAGS, the second one you usually put into LDLIBS).
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SwiftMango almost 5 years@Victor that is required "metadata" for cgo to find the proper files to link and call
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George Y about 3 yearsInteresting that under
-L .
it will check/usr/lib/
instead.