Go code and C code have to agree on how resources like address space, signal handlers, and thread TLS slots are to be shared — and when I say agree, I actually mean Go has to work around the C code's assumption. C code that can assume it always runs on one thread, or blithely be unprepared to work in a multi threaded environment at all.
C doesn't know anything about Go's calling convention or growable stacks, so a call down to C code must record all the details of the goroutine stack, switch to the C stack, and run C code which has no knowledge of how it was invoked, or the larger Go runtime in charge of the program.
It doesn't matter which language you’re writing bindings or wrapping C code with; Python, Java with JNI, some language using libFFI, or Go via cgo; it is C's world, you're just living in it.
