How's return value implemented in assembly level?

Question

int main(void){

printf("Hello World");

return 0;

}

How is 0 passed as return value in assembly level? Is there a dedicated CPU register for this job?

UPDATE

Here's the 2 tables on passing/return data in the pdf, but doesn't seems to have the exact info on how the calling convention of an API is determined and which register is used for storing return address:

Answer 1

That depends on the architecture. Just for a couple of examples, on x86 the EAX register is normally used for return values. On x86-64, it's RAX. On SPARC, it'll normally show up in %o0.

Answer 2

That's part of the application binary interface.

These days the return value and function parameters usually are passed in registers, because that is the most efficient option. Only if that gets too big for the available registers the stack is used.