; TAKEN FROM https://github.com/davidad/asm_concurrency/blob/master/os_dependent_stuff.asm
; syscalls
%ifidn __OUTPUT_FORMAT__,elf64
; http://lxr.linux.no/linux+v3.13.5/arch/x86/syscalls/syscall_64.tbl
  %define SYS_READ      0
  %define SYS_OPEN      2
  %define SYS_WRITE     1
  %define SYS_MMAP      9
  %define SYS_FTRUNCATE 77
  %define SYS_PWRITE    18
  %define SYS_FORK      57
  %define SYS_WAITID    247
  %define SYS_EXIT      60
%elifidn __OUTPUT_FORMAT__,macho64
; http://www.opensource.apple.com/source/xnu/xnu-1456.1.26/bsd/kern/syscalls.master
  %define SYS_READ      0x2000003
  %define SYS_OPEN      0x2000005
  %define SYS_WRITE     0x2000004
  %define SYS_MMAP      0x20000C5
  %define SYS_FTRUNCATE 0x20000C9
  %define SYS_PWRITE    0x200009A
  %define SYS_FORK      0x2000002
  %define SYS_WAITID    0x20000AD
  %define SYS_EXIT      0x2000001
%endif

; mmap() and mprotect() flags
%ifidn __OUTPUT_FORMAT__,elf64
; http://lxr.linux.no/linux+v3.13.5/include/uapi/asm-generic/mman-common.h
  %define MAP_SHARED   0x01
  %define MAP_PRIVATE  0x02
  %define MAP_FIXED    0x10
  %define MAP_ANON     0x20
  %define PROT_NONE     0x0
  %define PROT_READ     0x1
  %define PROT_WRITE    0x2
  %define PROT_EXEC     0x4
  %define PROT_SEM      0x8
  %define PROT_GROWSDOWN 0x01000000
  %define PROT_GROWSUP   0x02000000
%elifidn __OUTPUT_FORMAT__,macho64
; http://www.opensource.apple.com/source/xnu/xnu-2050.18.24/bsd/sys/mman.h
  %define MAP_SHARED    0x001
  %define MAP_PRIVATE   0x002
  %define MAP_FIXED     0x010
  %define MAP_RENAME    0x020
  %define MAP_NORESERVE 0x040
  %define MAP_INHERIT   0x080
  %define MAP_NOEXTEND  0x100
  %define MAP_SEMAPHORE 0x200
  %define MAP_NOCACHE   0x400
  %define MAP_JIT       0x800
  %define MAP_FILE      0x0000
  %define MAP_ANON      0x1000
  %define PROT_NONE     0x0
  %define PROT_READ     0x1
  %define PROT_WRITE    0x2
  %define PROT_EXEC     0x4
%endif

%define STDIN_FILENO 0
%define STDOUT_FILENO 1
%define STDERR_FILENO 2


global start, _start, putc, putint, getc, exit, _builtin_malloc, _builtin_outofbounds
default rel

extern main

section .text
start:
_start:
	and rsp, -16  ; make stack 16-byte aligned
	call main
	mov rdi, rax
	mov eax, SYS_EXIT
	syscall
	jmp $

putc:
	push rax
	push rdi
	push rsi
	push rdx
	push rcx
	push r11
	mov eax, SYS_WRITE
	mov edi, STDOUT_FILENO
	lea rsi, [rsp+56]
	mov edx, edi
	syscall
	pop r11
	pop rcx
	pop rdx
	pop rsi
	pop rdi
	pop rax
	ret

putint:
	push rdi
	push rsi
	push rax
	push rbx
	push rcx
	push rdx
	push r11
	mov rax, [rsp+64]
	mov ebx, 18
	test rax, rax
	jz .numzero

	mov ecx, 10

.strlp:
	xor edx, edx
	div rcx
	add dl, '0'
	dec rbx
	mov [rsp+rbx], dl
	test rax, rax
	jnz .strlp
	jmp .strdone

.numzero:
	dec rbx
	mov byte [rsp+rbx], '0'
	jmp .strdone

.strdone:
	mov eax, SYS_WRITE
	mov edi, 1
	lea rsi, [rsp+rbx]
	mov edx, 18
	sub rdx, rbx
	syscall

	pop r11
	pop rdx
	pop rcx
	pop rbx
	pop rax
	pop rsi
	pop rdi
	ret

getc:
	push rdi
	push rsi
	push rdx
	push rcx
	push r11
	mov eax, SYS_READ
	mov edi, STDIN_FILENO
	lea rsi, [rsp-1]
	mov edx, 1
	syscall
	cmp rax, 1
	jne .fail
	xor eax, eax
	mov al, [rsp-1]
.finish:
	pop r11
	pop rcx
	pop rdx
	pop rsi
	pop rdi
	ret
.fail:
	mov rax, -1
	jmp .finish

exit:
	mov rdi, [rsp+8]
	mov eax, SYS_EXIT
	syscall
	jmp $

strlen:
	push rbx
	push rcx
	push rdx
	push rdi
	push rsi
	mov rsi, [rsp+8]  ; string data pointer
	mov rcx, [rsi-8]  ; array size
	xor edx, edx  ; string walker
	cmp rcx, 16
	jb .short

	movdqa [rsp], xmm1
	movdqa [rsp-16], xmm2

	mov rax, rcx  ; now array size
	lea rbx, [rax-16]
	pxor xmm2, xmm2
.lp:
	movdqu xmm1, [rsi+rdx]
	pcmpistri xmm1, xmm2, 0x08
	js .nullfound
	add rdx, 16
	cmp rdx, rbx
	jbe .lp

	movdqa xmm2, [rsp-16]
	movdqa xmm1, [rsp]

	cmp rdx, rax
	je .nonull

	mov rcx, rax
	sub rcx, rdx

.short:
	mov al, [rsi+rdx]
	inc rdx
	test al, al
	loopnz .short
	jnz .nonull
	lea rax, [rdx-1]
	pop rsi
	pop rdi
	pop rdx
	pop rcx
	pop rbx
	ret

.nullfound:
	add rdx, rcx
	mov rax, rdx
	pop rsi
	pop rdi
	pop rdx
	pop rcx
	pop rbx
	ret

.nonull:
	mov edi, STDERR_FILENO
	lea rsi, [nonull_msg]
	mov edx, nonull_msg.len
	mov eax, SYS_WRITE
	syscall
	jmp exit255

_builtin_malloc:
	push rdi
	push rsi
	push rdx
	push r8
	push r9
	push r10
	push r11
	push rcx
	xor edi, edi
	mov rsi, [rsp+72]
	mov edx, PROT_READ | PROT_WRITE
	mov r10d, MAP_ANON | MAP_PRIVATE
	mov r8d, -1
	xor r9d, r9d
	mov eax, SYS_MMAP
	syscall
	pop rcx
	pop r11
	pop r10
	pop r9
	pop r8
	pop rdx
	pop rsi
	pop rdi
	ret

_builtin_outofbounds:
	mov edi, STDERR_FILENO
	lea rsi, [outofbounds_msg]
	mov rdx, outofbounds_msg.len
	mov eax, SYS_WRITE
	syscall
exit255:
	mov edi, 255
	mov eax, SYS_EXIT
	syscall
	jmp $


section .data
outofbounds_msg: db "Runtime Error: Out-of-bounds array access detected", 10
.len: equ $ - outofbounds_msg
nonull_msg: db "Runtime Error: No null byte found in string", 10
.len: equ $ - nonull_msg