lang/src/arch/x86_64/encode.rs

use std::collections::HashMap;

use super::*;
use crate::backend::{LibImport, LinkedProgram, SymImport, SymTable, Symbol};
use util::*;

pub struct Encoder<'a> {
    pub data: Vec<u8>,
    pub sym_tab: SymTable<u64>,
    pub missing: Vec<(usize, Symbol)>,
    pub sym_refs: HashMap<Symbol, Vec<usize>>,
    pub program: &'a Program<X86_64>,
}

pub fn compile(p: &Program<X86_64>) -> Result<LinkedProgram<u64>, CompilerMsg> {
    let mut encoder = Encoder::new(p);

    p.encode_data(&mut encoder.data, &mut encoder.sym_tab);

    for f in &p.funcs {
        let addr = encoder.data.len();
        encoder.sym_tab.insert(f.sym, addr as u64);
        for instr in &f.instrs {
            compile_instr(&mut encoder, instr)?;
        }
    }

    for (pos, sym) in encoder.missing.drain(..) {
        let addr = encoder
            .sym_tab
            .get(sym)
            .ok_or(CompilerMsg::from(format!("missing symbol {sym:?}")))?;
        encoder.data[pos..pos + 4].copy_from_slice(&addr_offset(pos, addr))
    }

    let imports = p
        .external
        .iter()
        .map(|e| LibImport {
            name: e.file.clone(),
            syms: e
                .syms
                .iter()
                .map(|&s| SymImport {
                    name: p.sym_info(s).name.clone(),
                    usages: encoder.sym_refs.entry(s).or_default().clone(),
                })
                .collect(),
        })
        .collect();

    Ok(LinkedProgram {
        code: encoder.data,
        entry: p.entry.and_then(|e| encoder.sym_tab.get(e)),
        imports,
    })
}

type BInstr = crate::backend::Instr<X86_64>;
fn compile_instr(encoder: &mut Encoder, instr: &BInstr) -> Result<(), CompilerMsg> {
    match instr {
        BInstr::Asm(asm) => {
            for i in &asm.instrs {
                encoder.asm(*i)?;
            }
        }
        _ => todo!(),
    }
    Ok(())
}

impl Encoder<'_> {
    // assembly

    pub fn movi(&mut self, dst: RegWH, imm: u64) -> Result<(), CompilerMsg> {
        if dst.widthh == WidthH::B16 {
            self.data.push(0x66);
        }
        if dst.requires_rex() {
            self.data.push(rex(dst.widthh, 0, 0, dst));
        }
        if imm > dst.widthh.max() {
            return Err("immediate cannot fit in register".into());
        }
        let opcode = 0xb0 | ((dst.widthh.gt8() as u8) << 3);
        self.data.push(opcode | dst.base());
        self.data.extend(&imm.to_le_bytes()[..dst.widthh.bytes()]);
        Ok(())
    }

    pub fn movr(&mut self, dst: RegH, src: RegH, width: Width) {
        if width == Width::B16 {
            self.data.push(0x66);
        }
        if src.requires_rex(width) || dst.requires_rex(width) {
            self.data.push(rex(width, src, 0, dst));
        }
        self.data.push(0x88 | width.gt8() as u8);
        self.data.push(modrm_regs(src, dst));
    }

    pub fn movm(&mut self, reg: RegWH, offset: u32, val: u32) {
        self.data.extend([rex(1, reg, 0, 0), 0xc7]);
        self.modrm_regdisp(reg, offset);
        self.data.extend(val.to_le_bytes());
    }

    pub fn lea(&mut self, dst: RegWH, sym: Symbol) {
        self.data
            .extend([rex(1, dst, 0, 0), 0x8d, modrm_disp32(dst)]);
        self.sym_offset4(sym);
    }

    pub fn int(&mut self, code: u8) {
        self.data.extend([0xcd, code])
    }

    pub fn syscall(&mut self) {
        self.data.extend([0x0f, 0x05])
    }

    pub fn call(&mut self, sym: Symbol) {
        self.data.push(0xe8);
        self.sym_offset4(sym);
    }

    pub fn callm(&mut self, sym: Symbol) {
        self.data.extend([0xff, 0x15]);
        self.sym_offset4(sym);
    }

    pub fn ret(&mut self) {
        self.data.push(0xc3);
    }

    pub fn pushr(&mut self, reg: Reg) {
        if reg.gt8() {
            self.data.push(0x41);
        }
        self.data.push(0x50 | reg.base());
    }

    pub fn pushi(&mut self, imm: u32) {
        const U8: u32 = 2 << 8;
        if let 0..U8 = imm {
            self.data.push(0x6a);
            self.data.push(imm as u8);
        } else {
            self.data.push(0x68);
            self.data.extend(imm.to_le_bytes());
        }
    }

    pub fn pop(&mut self, reg: Reg) {
        if reg.gt8() {
            self.data.push(0x41);
        }
        self.data.push(0x58 | reg.base());
    }

    /// inserts a 32 bit offset from a symbol
    pub fn sym_offset4(&mut self, sym: Symbol) {
        let Some(addr) = self.sym_tab.get(sym) else {
            let pos = self.data.len();
            self.data.extend([0; 4]);
            if self.program.sym_info(sym).external {
                self.sym_refs.entry(sym).or_default().push(pos);
            } else {
                self.missing.push((pos, sym));
            }
            return;
        };
        self.data.extend(addr_offset(self.data.len(), addr));
    }

    pub fn asm(&mut self, instr: Instr) -> Result<(), CompilerMsg> {
        match instr {
            Instr::Movr { dst, src, width } => self.movr(dst, src, width),
            Instr::Movi { dst, imm } => self.movi(dst, imm)?,
            Instr::Movm { reg, offset, val } => self.movm(reg, offset, val),
            Instr::Int(code) => self.int(code),
            Instr::Syscall => self.syscall(),
            Instr::Lea { dst, sym } => self.lea(dst, sym),
            Instr::Call(sym) => self.call(sym),
            Instr::Callm(sym) => self.callm(sym),
            Instr::Ret => self.ret(),
            Instr::Pushr(reg) => self.pushr(reg),
            Instr::Pushi(imm) => self.pushi(imm),
            Instr::Pop(reg) => self.pop(reg),
            Instr::Sub => self.data.extend([0x48, 0x83, 0xec, 0x28]),
        }
        Ok(())
    }

    pub fn modrm_regdisp(&mut self, reg: impl Into<Reg>, disp: u32) {
        let reg = reg.into();
        let disp8 = disp < u8::MAX as u32;
        let mod_ = if disp8 { 0b01 } else { 0b10 };
        self.data.push(modrm(mod_, 0, reg.base()));
        if reg == rsp.reg {
            // SIB
            self.data.push(0x24);
        }
        if disp8 {
            self.data.push(disp as u8);
        } else {
            self.data.extend(disp.to_le_bytes());
        }
    }
}

impl<'a> Encoder<'a> {
    pub fn new(program: &'a Program<X86_64>) -> Self {
        Self {
            data: Default::default(),
            sym_tab: SymTable::new(program.sym_count()),
            missing: Default::default(),
            sym_refs: Default::default(),
            program,
        }
    }
}