Golang: multiple definition of CGO ported package - go

Question

I have 2 project, the first, name as A, there is a submodule a imported sqlite3(github.com/mattn/go-sqlite3). Another B project import A's submodule a, and in another submodule b, it also import the same sqlite3.
Both A and B put there imports under vendor dir(managed by govendor). My Golang version is go version go1.12 linux/amd64.
While build B (go build main.go), throwing following errors(too many, part of them):
/usr/local/go/pkg/tool/linux_amd64/link: running gcc failed: exit status 1
/tmp/go-link-281256755/000029.o: In function `callbackTrampoline':
/tmp/go-build/_cgo_export.c:25: multiple definition of `callbackTrampoline'
/tmp/go-link-281256755/000005.o:/tmp/go-build/_cgo_export.c:25: first defined here
/tmp/go-link-281256755/000029.o: In function `stepTrampoline':
...
/home/xxx/go/src/gitlab.xxxxxxxxx.com/xxxxxxxxx-tools/A/vendor/github.com/mattn/go-sqlite3/sqlite3.go:129: multiple definition of `_sqlite3_result_text'
/tmp/go-link-281256755/000009.o:/home/xxx/go/src/gitlab.xxxxxxxxx.com/xxxxxxxxx-tools/A/vendor/github.com/mattn/go-sqlite3/sqlite3.go:129: first defined here
/tmp/go-link-281256755/000033.o: In function `_sqlite3_result_blob':
...
But building A works well. To testing the error, I started following demo, also with vendor inited by govendor, and build ok.
package main
import (
"database/sql"
"fmt"
"gitlab.xxxxxxxxx.com/xxxxxxxxxxxxxxx/A/a"
_ "github.com/mattn/go-sqlite3"
)
func main() {
fmt.Println(a.ModuleVariable) // use submodule `a` just like B is doing
_, _ = sql.Open(`sqlite3`, `test.db`) // use sqlite too
}
I think the compiler first compile A's sqlite3, objects are created under /tmp/go-link-281256755/000005.o (but no this dir after building), then compile B's importing of sqlite3 and also create a object contains the same-name function, then the compiler find 2 same-name symbols, the linking failed.
How to fix these situation? Is there any golang env settings to avoid these?
After I remove the sqlite3 package under vendor both of A and B, they both use the sqlite3 under ~/go/src/github.com/mattn/go-sqlite3/, they all build ok. But I can't do these, due to project A's deploy platform, I must put all dependencies under vendor, is there any another option to use multiple import with the same package?

Answer 1

For the cgo's issue of linking error "multiple definition of ...", the (work-around) solution is dependent on the nature of the linked C codes:
If two Go packages link to the same C codes (libraries), you should pass option --allow-multiple-definition to the linker (see ld man page), either via command options
go build --ldflags '-extldflags "-Wl,--allow-multiple-definition"',
or via #cgo directive in Go source of the packages linking to C codes:
//#cgo LDFLAGS: -Wl,--allow-multiple-definition
import "C"
If two Go packages link to different C codes containing some functions & variables with the same names, you should refactor those C codes:
Make sure to put keyword static to all declarations whose usage is within that C object only (not intended to be linked to Go nor to other C objects).
Find some way to do name mangling or put those duplicated identifiers into different namespaces (like in C++). It would be better if cgo supported some mechanism to do automatic namespacing using Go package name, but until now (2020) you must do it yourself. The C preprocessor's "token pasting" operator ## may help in this namespacing task. Eg.
//File: my_package1.h
#define NS(id) my_package1_ ## id
void NS(my_function1)(int);
void NS(my_function2)(float);
char NS(my_shared_var);
If you have any C function definition in the Go source, like in this question, you must move those definitions into a separate C source file under the same package folder, leaving only declarations in the Go source.