Aski: Modern Assembly

Aski's meant to replace Assembly's painful and unintuitive linear syntax.

cmp rax, 0
jne .ne
mov rsi, my_text
lea rsi, [rsi+8]
mov [rsi], 0
.ne:

(Oh how it burns my eyes!)

It takes thorough effort to even understand what's going on here. What madness! With Aski, the program's intent becomes a lot clearer.

if $rax == 0 {
	$rsi = my_text + 8
	$*rsi = 0
}

Here we can clearly see my_text is getting null terminated at the 8th byte. So why was it so obscure in the Assembly code? Well, Assembly, due to it's linear nature, makes it difficult to see the path code execution takes and why. In addition, simple tasks (like writing a null byte to the end of a string) can end up to be way more instructions than what you'd expect. Although Aski compiles down to the same assembly code, people learning Assembly can get a feel and build an intution for Assembly by matching Aski statements with their corresponding Assembly output.

Now let's go over the semantics of language.

Syntax

All Aski code given to the compiler is converted to Assembly to allow Assembly newbies to read it.

Aski is aimed to resemble C syntax, while aimed to execute like Assembly instructions would. This means, like assembly, you manipulate the registers yourself!

$rax = 2

is fundamentally the same as

mov rax, 2

Though, to keep things easy for those new to Assembly, you can also do

$rax = $rax + $rsi * 4 * 2 + $rdi

which will expand into

lea rsi, [rsi*8]
add rax, rsi
add rax, rdi

or some equivilent.

Comments

Comments follow traditional assembly syntax, using semicolons.

; this is a comment!

Functions

Defining a function can be done like so.

fn foo {

}

Return instructions are automatically generated at the end of the function, so don't worry about having to add them yourself!

Calling a function is also very easy!

call(foo)

You can also expose a function to the linker by using the extern keyword. You'll want to do this for your _start function.

extern fn _start() {

}

Constants and Buffers

A constant string, number, or any other read only data can be marked with the const keyword. For example,

const hello = "hello word!"

Strings are not null terminated. If you'd like, you can terminate them yourselves.

Buffers are similar! use the let keyword.

let user_input: [byte, 32]

Woah, woah, woah! What's this [byte, 32] thing? Well, that's the integrated type system. Let's go over it really quickly.

Type System

Types specify the size of each unit as well as the amount of units. For example, in the previous example the size of the unit was a byte and the buffer was 32 bytes. But, if we change byte to qword, each unit will be 8 bytes long, so that'd mean the entire buffer would be 256 bytes!

let chunks: [qword, 32]
; that's 256 bytes!

To obtain the bytes occupied by a variable, just use the sizeof() function.

$rax = sizeof(chunks) - 1
; 255

Control Flow

Currently, if statements are the only implemented control flow structure, besides call. Our modular compiler will allow us to while and for loops with not much more effort, but due to time constraints we're only working with if statements. They are similar to Rust if statements.

if $rax * 2 + rsi != $rdx - 3 {
  ; code here
}

Inline Assembly

Something you need that Aski doesn't have? Use some inline assembly!

#syscall

Just prefix with a hashtag.

Example

Here's an example program that takes a file name and spits out it's contents!

const hello = "welcome to fs reader!"

const file_question = "what file would you like to read?"

const no_input_err = "no input given!"

let user_buf: [byte, 128]

; 64 chunks to store file data
let file_data: [qword, 64]

extern fn _start {
    $rsi = hello
    $rdx = sizeof(hello)
    call(print)

    call(menu)
}

fn menu {
    $rsi = file_question
    $rdx = sizeof(file_question)
    call(print)

    $rsi = user_buf
    $rdx = sizeof(user_buf)
    call(read_input)

    ; account for newline
    if $rax == 1 {
        $rsi = no_input_err
        $rdx = sizeof(no_input_err)
        call(print)
        call(exit)
    }

    ; null terminate input & remove newline
    $rsi = user_buf
    $rdi = $rsi + $rax - 1
    $*rdi = 0

    $rdi = user_buf
    call(open)

    ; give fd of file to rdi
    $rdi = $rax
    $rax = 0
    $rsi = file_data
    $rdx = sizeof(file_data)
    #syscall

    $rdx = $rax
    $rsi = file_data
    call(print)

    call(menu)
}

fn read_input {
    $rax = 0
    $rdi = 0
    #syscall
}

; prints the string in rsi and size in rdx
fn print {
    ; sys_write
    $rax = 1
    ; stdout
    $rdi = 1
    #syscall
}

fn exit {
    $rax = 60
    $rdi = 0
    #syscall
}

fn open {
    $rax = 2
    $rsi = 0
    $rdx = 0
    #syscall
}