# A Linux amd64 assembly program in meta5ix using gas syntax that
# copies stdin to stdout, like cat.  This generates a “compiler” that
# consumes no input and compiles the empty string to the desired amd64
# program.

- program: body
- body:
        macros  
        {.bss}
@{buf:}
        {.equiv bufsiz, 128}
        {.fill bufsiz, 1, 0}
        {.text}
        {.globl _start}
@{_start:}
        {read \$0, \$buf, \$bufsiz}
        {cmp \$0, %rax}
        {jle done}
        {write \$1, \$buf, %rax}
        {jmp _start}
@{done:}
        {exit \$0}

# Hmm, I guess the system call numbers change when we use the
# `syscall` instruction instead of int $0x80.
# <https://github.com/torvalds/linux/blob/v3.13/arch/x86/syscalls/syscall_64.tbl#L69>
# has the right ones, and
# <https://blog.packagecloud.io/eng/2016/04/05/the-definitive-guide-to-linux-system-calls/#using-syscall-system-calls-with-your-own-assembly>
# says the first six arguments go in %rdi, %rsi, %rdx, %r10, %r8, and
# %r9, and the return value is in %rax.  We could define syscall,
# read, write, etc., macros as meta5ix macros, but gas macros can take
# *parameters*.
- macros:
        {.macro sys4 n a b c d}
        {mov \\a, %rdi}
        {mov \\b, %rsi}
        {mov \\c, %rdx}
        {mov \\d, %r10}
        {mov \$\\n, %rax}
        {syscall}
        {.endm}

        {.macro exit k}
        {sys4 60 \\k \$0 \$0 \$0}
        {.endm}

        {.macro read fd buf count}
        {sys4 0 \\fd \\buf \\count \$0}
        {.endm}

        {.macro write fd buf count}
        {sys4 1 \\fd \\buf \\count \$0}
        {.endm}