forked from AbleOS/holey-bytes
105 lines
3.1 KiB
Rust
105 lines
3.1 KiB
Rust
//! Holey Bytes Assembler
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//!
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//! Some people claim:
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//! > Write programs to handle text streams, because that is a universal interface.
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//!
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//! We at AbleCorp believe that nice programatic API is nicer than piping some text
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//! into a program. It's less error-prone and faster.
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//!
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//! So this crate contains both assembleer with API for programs and a text assembler
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//! for humans to write
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#![no_std]
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extern crate alloc;
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mod macros;
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use {
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alloc::{vec, vec::Vec},
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hashbrown::HashSet,
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};
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/// Assembler
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///
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/// - Opcode-generic, instruction-type-specific methods are named `i_param_<type>`
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/// - You likely won't need to use them, but they are here, just in case :)
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/// - Instruction-specific methods are named `i_<instruction>`
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pub struct Assembler {
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pub buf: Vec<u8>,
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pub sub: HashSet<usize>,
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}
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impl Default for Assembler {
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fn default() -> Self {
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Self {
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buf: vec![0; 3],
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sub: Default::default(),
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}
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}
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}
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hbbytecode::invoke_with_def!(macros::text::gen_text);
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impl Assembler {
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hbbytecode::invoke_with_def!(macros::asm::impl_asm);
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/// Append 12 zeroes (UN) at the end and add magic to the begining
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///
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/// # HoleyBytes lore
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///
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/// In reference HBVM implementation checks are done in
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/// a separate phase before execution.
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///
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/// This way execution will be much faster as they have to
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/// be done only once.
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///
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/// There was an issue. You cannot statically check register values and
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/// `JAL` instruction could hop at the end of program to some byte, which
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/// will be interpreted as some valid opcode and VM in attempt to decode
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/// the instruction performed out-of-bounds read which leads to undefined behaviour.
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///
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/// Several options were considered to overcome this, but inserting some data at
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/// program's end which when executed would lead to undesired behaviour, though
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/// not undefined behaviour.
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///
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/// Newly created `UN` (as UNreachable) was chosen as
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/// - It was a good idea to add some equivalent to `ud2` anyways
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/// - It was chosen to be zero
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/// - What if you somehow reached that code, it will appropriately bail :)
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/// - (yes, originally `NOP` was considered)
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///
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/// Why 12 bytes? That's the size of largest instruction parameter part.
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pub fn finalise(&mut self) {
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self.buf.extend([0; 12]);
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self.buf[0..4].copy_from_slice(&0xAB1E0B_u32.to_le_bytes());
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}
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}
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/// Immediate value
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///
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/// # Implementor notice
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/// It should insert exactly 8 bytes, otherwise output will be malformed.
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/// This is not checked in any way
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pub trait Imm {
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/// Insert immediate value
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fn insert(&self, asm: &mut Assembler);
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}
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/// Implement immediate values
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macro_rules! impl_imm_le_bytes {
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($($ty:ty),* $(,)?) => {
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$(
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impl Imm for $ty {
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#[inline(always)]
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fn insert(&self, asm: &mut Assembler) {
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// Convert to little-endian bytes, insert.
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asm.buf.extend(self.to_le_bytes());
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}
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}
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)*
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};
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}
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impl_imm_le_bytes!(u64, i64, f64);
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