• Lucy :3@feddit.org
        0·
        27 days ago

        Should ≠ Needs to

        You can do it, and it will work, but it’s unclean and not best-practice. I wouldn’t be surprised if it’s undefined behaviour.

        • xmunk@sh.itjust.works
          1·
          27 days ago

          Just to clarify. It is defined behavior - there’s plenty of undefined behavior in C but that ain’t one of them.

          • FuckBigTech347@lemmygrad.ml
            1·
            27 days ago

            Interesting feature, I had no idea. I just verified this with gcc and indeed the return register is always set to 0 before returning unless otherwise specified.

            spoiler 
            int main(void)
{
    int foo = 10;
}

            produces:

            push   %rbp
mov    %rsp,%rbp
movl   $0xa,-0x4(%rbp) # Move 10 to stack variable
mov    $0x0,%eax       # Return 0
pop    %rbp
ret

            int main(void)
{
    int foo = 10;
    return foo;
}

            produces:

            push   %rbp
mov    %rsp,%rbp
movl   $0xa,-0x4(%rbp) # Move 10 to stack variable
mov    -0x4(%rbp),%eax # Return foo
pop    %rbp
ret