Recently, I needed to debug a particularly nasty interaction between two programs, one of which was a go tool. To get further in understanding the issue, I had to compile a little test program with cgo, the dreaded (by go programmers) compilation mode that allows go programs to call C code. Unfortunately, it’s a bit difficult to find out what to concretely do in order to build a program with cgo.

As with all semi-taboo knowledge¹, there seems to be a strong reluctance in the respective community to providing straightforward guidance on how do what you want (in this case, build a program with cgo which is discouraged and intensely disliked but is an integral part of building several popular & working go programs). Well, we’ll show them!

There are two main things you need to do: First, explicitly opt out of disabling the usage of the cgo compiler by setting CGO_ENABLED=1 on the compiler’s process environment. (This defaults to on, but your environment might have it turned off! Best to explicitly enable it.)

Second, you also have to provide the compiler a reason in code to compile your code with cgo: You have to make an FFI call into C. The easiest way that Andrew pointed me at is to use call a no-op C function from a go init() function.

This looks like the following:

package main

/*
int dummy(void) { return 42; }
*/
import "C"

func init() {
    C.dummy()
}

In order to make a program that can optionally be compiled with cgo and the native go complier, I structured the cgo-enabling parts such that the init function above lives in a file enablecgo.go, and starts with a line that says // +build enablecgo. You can find the whole source code in my bug report repro repo.

To build the app from that repo, you use the following commandlines:

• without cgo (native go compiler): go build ./
• with cgo: env CGO_ENABLED=1 go build -tags enablecgo

If you landed on this page, I hope it can help you get further in your debugging journey, and hope that the pain stops soon.