proposal: cgo: c code can call c function that defined in another cgo package

[bronze1man]

Please answer these questions before submitting your issue. Thanks!

What version of Go are you using (go version)?

go version go1.7.5 darwin/amd64

What operating system and processor architecture are you using (go env)?

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH=""
GORACE=""
GOROOT="/usr/local/go"
GOTOOLDIR="/usr/local/go/pkg/tool/darwin_amd64"
CC="clang"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/m9/qtbxkp6s3p96fk54rln7qhj80000gp/T/go-build255881879=/tmp/go-build -gno-record-gcc-switches -fno-common"
CXX="clang++"
CGO_ENABLED="1"

What did you do?

• define a c function in a .c file in one cgo package of in my project (GOPATH)
• define the c function prototype again and call that c function in another cgo package in my project.

What did you expect to see?

Compile success.

What did you see instead?

Compile fail.

[bronze1man]

I managed to implement this feature with go1.7.5 with darwin/ios/linux/android.

I have test that changeset in mac/ios/android os.

Here is the changeset:

diff --git a/src/cmd/go/build.go b/src/cmd/go/build.go
index 3c0b994..f3b9515 100644
--- a/src/cmd/go/build.go
+++ b/src/cmd/go/build.go
@@ -3348,7 +3355,15 @@ func (b *builder) cgo(p *Package, cgoExe, obj string, pcCFLAGS, pcLDFLAGS, cgofi
        if pie { // we need to use -pie for Linux/ARM to get accurate imported sym
                cgoLDFLAGS = append(cgoLDFLAGS, "-pie")
        }
-       if err := b.gccld(p, dynobj, cgoLDFLAGS, linkobj); err != nil {
+       symLDFlAGS := cgoLDFLAGS
+       if goos=="darwin"{
+               // clang
+               symLDFlAGS= append(symLDFlAGS,"-flat_namespace","-Wl,-undefined,warning")
+       }else{
+               // gcc
+               symLDFlAGS= append(symLDFlAGS,"-Wl,--unresolved-symbols=ignore-all")
+       }
+       if err := b.gccld(p, dynobj, symLDFlAGS, linkobj); err != nil {
                return nil, nil, err
        }
        if pie { // but we don't need -pie for normal cgo programs

I do not know how to port this feature to go1.8

[bradfitz]

This seems like a bad idea and breaks backwards compatibility.

Also, We do not accept changes on the issue tracker. Code must only come via https://golang.org/doc/contribute.html

Even if this feature were approved, that code is not gofmt'd and does not have tests. Its detection of clang-vs-gcc is also overly simplistic. In the future, please wait for approval before sending code.

[bradfitz]

I suggest you discuss on the mailing list about your actual problem before jumping to a solution. (See http://xyproblem.info/)

For questions about Go, see https://golang.org/wiki/Questions.

[bronze1man]

I add this feature to my own go1.7.5, so that I can write a rpc that can call objective c from golang function/call golang function from objective c in every package without write one line about complex cgo stuff.
Without this feature, I just need every package have same c function implement that marshal stuff.

I do not understand why you guys do not even want to discuss it.

"This seems like a bad idea and breaks backwards compatibility."
This proposal do not break backwards compatibility. Normal golang code can run on this.You just can call bigger range of code.

I looks like I have to port those changs to go1.8 myself. if I want to upgrade to that golang version.
I take a lot of effort to ask your guys to merge this pr.
I think I can just save that time to add more powful feature to my own golang like package

[ianlancetaylor]

Brad didn't say that we don't want to discuss it, he said that we want to discuss it on a mailing list instead of the issue tracker. Thanks.