wasmtime/winch/codegen/src/isa/aarch64/masm.rs

use super::{
    address::Address,
    asm::{Assembler, Operand},
    regs,
};
use crate::{
    abi::local::LocalSlot,
    codegen::CodeGenContext,
    isa::reg::Reg,
    masm::{CalleeKind, DivKind, MacroAssembler as Masm, OperandSize, RegImm, RemKind},
};
use cranelift_codegen::{settings, Final, MachBufferFinalized};

/// Aarch64 MacroAssembler.
pub(crate) struct MacroAssembler {
    /// Low level assembler.
    asm: Assembler,
    /// Stack pointer offset.
    sp_offset: u32,
}

// Conversions between generic masm arguments and aarch64 operands.

impl From<RegImm> for Operand {
    fn from(rimm: RegImm) -> Self {
        match rimm {
            RegImm::Reg(r) => r.into(),
            RegImm::Imm(imm) => Operand::Imm(imm),
        }
    }
}

impl From<Reg> for Operand {
    fn from(reg: Reg) -> Self {
        Operand::Reg(reg)
    }
}

impl From<Address> for Operand {
    fn from(addr: Address) -> Self {
        Operand::Mem(addr)
    }
}

impl MacroAssembler {
    /// Create an Aarch64 MacroAssembler.
    pub fn new(shared_flags: settings::Flags) -> Self {
        Self {
            asm: Assembler::new(shared_flags),
            sp_offset: 0u32,
        }
    }
}

impl Masm for MacroAssembler {
    type Address = Address;

    fn prologue(&mut self) {
        let lr = regs::lr();
        let fp = regs::fp();
        let sp = regs::sp();
        let addr = Address::pre_indexed_from_sp(-16);

        self.asm.stp(fp, lr, addr);
        self.asm.mov_rr(sp, fp, OperandSize::S64);
        self.move_sp_to_shadow_sp();
    }

    fn epilogue(&mut self, locals_size: u32) {
        assert!(self.sp_offset == locals_size);

        let sp = regs::sp();
        if locals_size > 0 {
            self.asm
                .add_ir(locals_size as u64, sp, sp, OperandSize::S64);
            self.move_sp_to_shadow_sp();
        }

        let lr = regs::lr();
        let fp = regs::fp();
        let addr = Address::post_indexed_from_sp(16);

        self.asm.ldp(fp, lr, addr);
        self.asm.ret();
    }

    fn reserve_stack(&mut self, bytes: u32) {
        if bytes == 0 {
            return;
        }

        let sp = regs::sp();
        self.asm.sub_ir(bytes as u64, sp, sp, OperandSize::S64);
        self.move_sp_to_shadow_sp();

        self.increment_sp(bytes);
    }

    fn free_stack(&mut self, _bytes: u32) {
        todo!()
    }

    fn local_address(&mut self, local: &LocalSlot) -> Address {
        let (reg, offset) = local
            .addressed_from_sp()
            .then(|| {
                let offset = self.sp_offset.checked_sub(local.offset).expect(&format!(
                    "Invalid local offset = {}; sp offset = {}",
                    local.offset, self.sp_offset
                ));
                (regs::shadow_sp(), offset)
            })
            .unwrap_or((regs::fp(), local.offset));

        Address::offset(reg, offset as i64)
    }

    fn address_from_sp(&self, _offset: u32) -> Self::Address {
        todo!()
    }

    fn address_at_sp(&self, _offset: u32) -> Self::Address {
        todo!()
    }

    fn store(&mut self, src: RegImm, dst: Address, size: OperandSize) {
        let src = match src {
            RegImm::Imm(imm) => {
                let scratch = regs::scratch();
                self.asm.load_constant(imm as u64, scratch);
                scratch
            }
            RegImm::Reg(reg) => reg,
        };

        self.asm.str(src, dst, size);
    }

    fn call(&mut self, _callee: CalleeKind) {
        todo!()
    }

    fn load(&mut self, src: Address, dst: Reg, size: OperandSize) {
        self.asm.ldr(src, dst, size);
    }

    fn pop(&mut self, _dst: Reg) {
        todo!()
    }

    fn sp_offset(&self) -> u32 {
        self.sp_offset
    }

    fn finalize(self) -> MachBufferFinalized<Final> {
        self.asm.finalize()
    }

    fn mov(&mut self, src: RegImm, dst: RegImm, size: OperandSize) {
        self.asm.mov(src.into(), dst.into(), size);
    }

    fn add(&mut self, dst: RegImm, lhs: RegImm, rhs: RegImm, size: OperandSize) {
        self.asm.add(rhs.into(), lhs.into(), dst.into(), size);
    }

    fn sub(&mut self, _dst: RegImm, _lhs: RegImm, _rhs: RegImm, _size: OperandSize) {
        todo!()
    }

    fn mul(&mut self, _dst: RegImm, _lhs: RegImm, _rhs: RegImm, _size: OperandSize) {
        todo!()
    }

    fn div(&mut self, _context: &mut CodeGenContext, _kind: DivKind, _size: OperandSize) {
        todo!()
    }

    fn rem(&mut self, _context: &mut CodeGenContext, _kind: RemKind, _size: OperandSize) {
        todo!()
    }

    fn zero(&mut self, reg: Reg) {
        self.asm.load_constant(0, reg);
    }

    fn push(&mut self, reg: Reg) -> u32 {
        // The push is counted as pushing the 64-bit width in
        // 64-bit architectures.
        let size = 8u32;
        self.reserve_stack(size);
        let address = Address::from_shadow_sp(size as i64);
        self.asm.str(reg, address, OperandSize::S64);

        self.sp_offset
    }

    fn address_from_reg(&self, reg: Reg, offset: u32) -> Self::Address {
        Address::offset(reg, offset as i64)
    }
}

impl MacroAssembler {
    fn increment_sp(&mut self, bytes: u32) {
        self.sp_offset += bytes;
    }

    // Copies the value of the stack pointer to the shadow stack
    // pointer: mov x28, sp

    // This function is usually called whenever the real stack pointer
    // changes, for example after allocating or deallocating stack
    // space, or after performing a push or pop.
    // For more details around the stack pointer and shadow stack
    // pointer see the docs at regs::shadow_sp().
    fn move_sp_to_shadow_sp(&mut self) {
        let sp = regs::sp();
        let shadow_sp = regs::shadow_sp();
        self.asm.mov_rr(sp, shadow_sp, OperandSize::S64);
    }
}