fasm port for OpenBSD amd64

Based on the Linux x64 port, I've ported fasm to OpenBSD on amd64 (i386 is available in packages and as devel/fasm in ports). The libc port could not be used here as OpenBSD does not support i386 binaries on amd64.

The attached archive contains the source and the binary, so it can be self-compiled natively. Some things are marked as TODO in the source, and the code could do with improvements in places, but it does work.

You must link native executables using ld.bfd -nopie, the normal linker will not work due to how it treats the .note.openbsd.ident section when it isn't marked explicitly as a note (fasm does not support that attribute for ELF).

Notes:

OpenBSD does not support Linux's MAP_32BIT, so if the program break is above 4GB it will error, however that should never happen as we get the break using an external symbol rather than brk(0)
OpenBSD's syscall interface may or may not be stable from release to release (I couldn't find an official statement either way) -- a possible solution to this in the future is to go through libc instead

At a minimum, you need this to assemble a working native executable:

Code:

format ELF64

section '.note.openbsd.ident' align 2
        dd 8,4,1
        db 'OpenBSD',0
        dd 0

public _start
_start:
        mov rdi,0
        mov rax,1  ; SYS_exit
        syscall

Have fun!