ABI question, porting ports to amd64

[Marco van de Voort]

> I read the ABI info on x86-64.org, and objdumped some linux and freebsd
> code, and I ran into a linux<->freebsd difference something I can't figure
> out:

Answering my own question:

FreeBSD uses the gcc mechanism to build the same parameterlist for a syscall
like for a normal procedure. (to avoid having to shift params)

The register for the 4th parameter for gcc is %rcx, for the kernel it is
%r10. So gcc puts the 4th param in %rcx, and the move moves it to %r10 for
the kernel.