CGO: How to link static library across dependent packages?

[pat.s...@gmail.com]

Folks,

Two of my packages have dependency on the same C library. I have linked them successfully using the LDFLAGS directives.

But I'm facing a multiple definitions error when linking my project executable

Here is an overview of my project structure:

Pkg A -> depends on LIBA

Pkg B (imports Pkg A) -> and also depends on LIBA

Pkg Main imports B

Commands used to build: In Pkg Main directory: go build

Appreciate any thoughts on this issue

Thanks!

[Ian Lance Taylor]

On Wed, Oct 26, 2016 at 11:15 PM, <pat.s...@gmail.com> wrote:
>
> Two of my packages have dependency on the same C library. I have linked them
> successfully using the LDFLAGS directives.
>
> But I'm facing a multiple definitions error when linking my project
> executable
>
>
> Here is an overview of my project structure:
>
> Pkg A -> depends on LIBA
>
> Pkg B (imports Pkg A) -> and also depends on LIBA
>
> Pkg Main imports B
>
>
> Commands used to build: In Pkg Main directory: go build

What is the actual error?

ian

[pat.s...@gmail.com]

Hi Ian,

Here is the build output -- 

FYI -- The path: /<path>/goLang/goCode/src/eventbridge/EventBridge.c was where I had compiled the C library using the gcc toolchain. I copied this compiled library to my project and statically linked it.

Path to my project is at  /<path>/goLang/goCode/src/agent/

>echo $SHELL

/bin/csh

>pwd

/<path>/goLang/goCode/src/agent

>echo $GOPATH

/<path>/goLang/goCode

>go version

go version go1.7.1 linux/amd64

>gcc -v

Using built-in specs.

Target: x86_64-redhat-linux

Configured with: ../configure --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-bootstrap --enable-shared --enable-threads=posix --enable-checking=release --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-gnu-unique-object --enable-languages=c,c++,objc,obj-c++,java,fortran,ada --enable-java-awt=gtk --disable-dssi --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-1.5.0.0/jre --enable-libgcj-multifile --enable-java-maintainer-mode --with-ecj-jar=/usr/share/java/eclipse-ecj.jar --disable-libjava-multilib --with-ppl --with-cloog --with-tune=generic --with-arch_32=i686 --build=x86_64-redhat-linux

Thread model: posix

gcc version 4.4.7 20120313 (Red Hat 4.4.7-17) (GCC)

>go build

# agent

/<path>/goLang/go/pkg/tool/linux_amd64/link: running gcc failed: exit status 1

/<path>/tmp/go-link-022070709/000001.o: In function `putStringToBuffer':

/<path>/goLang/goCode/src/eventbridge/EventBridge.c:31: multiple definition of `putStringToBuffer'

/<path>/tmp/go-link-022070709/000000.o:/<path>/goLang/goCode/src/eventbridge/EventBridge.c:31: first defined here

/<path>/tmp/go-link-022070709/000001.o: In function `ReceiveEventBuffer':

/<path>/goLang/goCode/src/eventbridge/EventBridge.c:446: multiple definition of `ReceiveEventBuffer'

/<path>/tmp/go-link-022070709/000000.o:/<path>/goLang/goCode/src/eventbridge/EventBridge.c:446: first defined here

/<path>/tmp/go-link-022070709/000001.o: In function `getStringFromBuffer':

/<path>/goLang/goCode/src/eventbridge/EventBridge.c:37: multiple definition of `getStringFromBuffer'

/<path>/tmp/go-link-022070709/000000.o:/<path>/goLang/goCode/src/eventbridge/EventBridge.c:37: first defined here

:

:

:

goes to point out multiple declaration error for each of the function defined in the library LIBA

Thanks!

Sriram

[pat.s...@gmail.com]

Correction in typo -- "*goes to point out multiple definition error for each of the function defined in the library LIBA"

goes to point out multiple definition error for each of the function defined in the library LIBA

[Ian Lance Taylor]

On Fri, Oct 28, 2016 at 9:36 PM, <pat.s...@gmail.com> wrote:
>
>>go build
> # agent
> /<path>/goLang/go/pkg/tool/linux_amd64/link: running gcc failed: exit status
> 1
> /<path>/tmp/go-link-022070709/000001.o: In function `putStringToBuffer':
> /<path>/goLang/goCode/src/eventbridge/EventBridge.c:31: multiple definition
> of `putStringToBuffer'
> /<path>/tmp/go-link-022070709/000000.o:/<path>/goLang/goCode/src/eventbridge/EventBridge.c:31:
> first defined here
> /<path>/tmp/go-link-022070709/000001.o: In function `ReceiveEventBuffer':
> /<path>/goLang/goCode/src/eventbridge/EventBridge.c:446: multiple definition
> of `ReceiveEventBuffer'
> /<path>/tmp/go-link-022070709/000000.o:/<path>/goLang/goCode/src/eventbridge/EventBridge.c:446:
> first defined here
> /<path>/tmp/go-link-022070709/000001.o: In function `getStringFromBuffer':
> /<path>/goLang/goCode/src/eventbridge/EventBridge.c:37: multiple definition
> of `getStringFromBuffer'
> /<path>/tmp/go-link-022070709/000000.o:/<path>/goLang/goCode/src/eventbridge/EventBridge.c:37:
> first defined here

This looks like your cgo comment, before the import "C", is actually
defining functions rather than simply declaring them. What does the
cgo comment look like?

Ian

[kumargv]

Hi Mate,

why Don't you try to make a static binary 

go build --ldflags ' -extldflags "-static"' filename.go

[pat.s...@gmail.com]

Its not defining the functions Ian. The issue is both the packages A and B are linking the same library

package A:

/*

#cgo LDFLAGS: -Bstatic  ${SRCDIR}/../lib/libeventbridge.a

*/

The same thing in package B:

/*

#cgo LDFLAGS: -Bstatic ${SRCDIR}/../lib/libeventbridge.a

*/

Please note: 

1. Without including the library in these packages, the linker of the individual package fails indicating that the definition of the functions used is not found.

2. Package B imports package A

Thanks,

Sriram

[pat.s...@gmail.com]

Can you please provide more info? If i use the below command to compile my project, the linker error still pops up.

Just to recap,

My packages A and B statically link a common library LIBA. Also, Package B imports A. Compilation of the individual packages is successful but when i try to create a binary (using package main which imports B) I get a linker error for redefinition of the library.

I understand that Im linking the library twice (once in package A and once in B) but I cant compile the individual packages without linking it in each of the packages.

package A:

package A

/*

#cgo LDFLAGS: -Bstatic  ${SRCDIR}/../lib/libeventbridge.a

*/

import "C"

The same thing in package B:

package B

import "A"

/*

#cgo LDFLAGS: -Bstatic ${SRCDIR}/../lib/libeventbridge.a

*/

import "C"

Thanks,

Sriram

[Ian Lance Taylor]

On Sat, Oct 29, 2016 at 10:22 AM, <pat.s...@gmail.com> wrote:
> Can you please provide more info? If i use the below command to compile my
> project, the linker error still pops up.
>
> Just to recap,
>
> My packages A and B statically link a common library LIBA. Also, Package B
> imports A. Compilation of the individual packages is successful but when i
> try to create a binary (using package main which imports B) I get a linker
> error for redefinition of the library.
>
>
> I understand that Im linking the library twice (once in package A and once
> in B) but I cant compile the individual packages without linking it in each
> of the packages.
>
>
> package A:
>
> package A
> /*
> #cgo LDFLAGS: -Bstatic ${SRCDIR}/../lib/libeventbridge.a
> */
> import "C"
>
>
> The same thing in package B:
>
> package B
>
> import "A"
> /*
> #cgo LDFLAGS: -Bstatic ${SRCDIR}/../lib/libeventbridge.a
> */
> import "C"

Please open an issue at https://golang.org/issue with a complete
standalone reproduction case. I'm not really sure what is going on.

Ian

[Sriram]

Sure will do that.. Thanks Ian

[bkirs...@gmail.com]

Did you find the solution to this problem?  I think I might have the same problem.

Also, if there is useful info, and it's not too much trouble, can you link to the issue you opened?

Thanks

On Sunday, October 30, 2016 at 9:18:27 AM UTC-7, Sriram wrote:

Sure will do that.. Thanks Ian

On Oct 30, 2016 9:37 PM, "Ian Lance Taylor" <ia...@golang.org> wrote:

[Sriram]

No, unfortunately I worked around the problem by redesigning the modules

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