I mean talking to Go from C or any other language as if Go was replacing a C library. Could not find low-level detail on this, but I remember it used to be very slow. E.g. PInvoke has an overhead of between 10 and 30 x86 instructions per call, which is quite small.

Actually I'm not sure if that is possible now to call Go from C via some C ABI/ABI. I looked into CGO in the past.