Why does go's compiler "gc" use a different calling convention than C?

Question

C uses the cdecl, which I've looked into and called with from assembly. It feels well enough, so why break the compatibility? Why was another convention needed?

Inflammable

Go allows multiple return values and gc uses segmented stacks. I'm not entirely sure, but I wouldn't be surprised if these features are related to the calling conventions. Afaik, the only way to return multiple values with cdecl is to return a pointer to a structure. – Celanese

C does not use the cdecl calling convention. Some implementations use it, and some use other calling conventions. – Maryettamaryjane

AFAIK the Google implementation of Go uses a calling convention that is equal to that of C except in the places where C can't express the concept Go uses (such as when there are multiple return values) – Gavan

Answer 1

Because there's no advantage in having the same calling convention. Go code and C code cannot call each other directly even when the calling convention would be the same because Go uses split stacks.

OTOH, it makes sense in gccgo, as gcc supports C split stacks for some architectures. And, IIRC, there the calling convention is because of that compatible. (More details here.)

Disclaimer: I didn't ever actually used gccgo.

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