//! HoleyBytes Virtual Machine //! //! All unsafe code here should be sound, if input bytecode passes validation. // # General safety notice: // - Validation has to assure there is 256 registers (r0 - r255) // - Instructions have to be valid as specified (values and sizes) // - Mapped pages should be at least 4 KiB pub mod mem; pub mod value; use { self::{mem::HandlePageFault, value::ValueVariant}, crate::validate, core::{cmp::Ordering, ops}, hbbytecode::{OpParam, ParamBB, ParamBBB, ParamBBBB, ParamBBD, ParamBBDH, ParamBBW, ParamBD}, mem::Memory, value::Value, }; /// HoleyBytes Virtual Machine pub struct Vm<'a, PfHandler, const TIMER_QUOTIENT: usize> { /// Holds 256 registers /// /// Writing to register 0 is considered undefined behaviour /// in terms of HoleyBytes program execution pub registers: [Value; 256], /// Memory implementation pub memory: Memory, /// Trap handler pub pfhandler: PfHandler, /// Program counter pub pc: usize, /// Program program: &'a [u8], /// Cached program length (without unreachable end) program_len: usize, /// Program timer timer: usize, } impl<'a, PfHandler: HandlePageFault, const TIMER_QUOTIENT: usize> Vm<'a, PfHandler, TIMER_QUOTIENT> { /// Create a new VM with program and trap handler /// /// # Safety /// Program code has to be validated pub unsafe fn new_unchecked(program: &'a [u8], traph: PfHandler) -> Self { Self { registers: [Value::from(0_u64); 256], memory: Default::default(), pfhandler: traph, pc: 0, program_len: program.len() - 12, program, timer: 0, } } /// Create a new VM with program and trap handler only if it passes validation pub fn new_validated(program: &'a [u8], traph: PfHandler) -> Result { validate::validate(program)?; Ok(unsafe { Self::new_unchecked(program, traph) }) } /// Execute program /// /// Program can return [`VmRunError`] if a trap handling failed pub fn run(&mut self) -> Result { use hbbytecode::opcode::*; loop { // Check instruction boundary if self.pc >= self.program_len { return Ok(VmRunOk::End); } // Big match // // Contribution guide: // - Zero register shall never be overwitten. It's value has to always be 0. // - Prefer `Self::read_reg` and `Self::write_reg` functions // - Extract parameters using `param!` macro // - Prioritise speed over code size // - Memory is cheap, CPUs not that much // - Do not heap allocate at any cost // - Yes, user-provided trap handler may allocate, // but that is not our »fault«. // - Unsafe is kinda must, but be sure you have validated everything // - Your contributions have to pass sanitizers and Miri // - Strictly follow the spec // - The spec does not specify how you perform actions, in what order, // just that the observable effects have to be performed in order and // correctly. // - Yes, we assume you run 64 bit CPU. Else ?conradluget a better CPU // sorry 8 bit fans, HBVM won't run on your Speccy :( unsafe { match *self.program.get_unchecked(self.pc) { UN => { self.decode::<()>(); return Err(VmRunError::Unreachable); } NOP => self.decode::<()>(), ADD => self.binary_op(u64::wrapping_add), SUB => self.binary_op(u64::wrapping_sub), MUL => self.binary_op(u64::wrapping_mul), AND => self.binary_op::(ops::BitAnd::bitand), OR => self.binary_op::(ops::BitOr::bitor), XOR => self.binary_op::(ops::BitXor::bitxor), SL => self.binary_op(|l, r| u64::wrapping_shl(l, r as u32)), SR => self.binary_op(|l, r| u64::wrapping_shr(l, r as u32)), SRS => self.binary_op(|l, r| i64::wrapping_shl(l, r as u32)), CMP => { // Compare a0 <=> a1 // < → -1 // > → 1 // = → 0 let ParamBBB(tg, a0, a1) = self.decode(); self.write_reg( tg, self.read_reg(a0) .cast::() .cmp(&self.read_reg(a1).cast::()) as i64, ); } CMPU => { // Unsigned comparsion let ParamBBB(tg, a0, a1) = self.decode(); self.write_reg( tg, self.read_reg(a0) .cast::() .cmp(&self.read_reg(a1).cast::()) as i64, ); } NOT => { // Logical negation let ParamBB(tg, a0) = self.decode(); self.write_reg(tg, !self.read_reg(a0).cast::()); } NEG => { // Bitwise negation let ParamBB(tg, a0) = self.decode(); self.write_reg( tg, match self.read_reg(a0).cast::() { 0 => 1_u64, _ => 0, }, ); } DIR => { // Fused Division-Remainder let ParamBBBB(dt, rt, a0, a1) = self.decode(); let a0 = self.read_reg(a0).cast::(); let a1 = self.read_reg(a1).cast::(); self.write_reg(dt, a0.checked_div(a1).unwrap_or(u64::MAX)); self.write_reg(rt, a0.checked_rem(a1).unwrap_or(u64::MAX)); } ADDI => self.binary_op_imm(u64::wrapping_add), MULI => self.binary_op_imm(u64::wrapping_sub), ANDI => self.binary_op_imm::(ops::BitAnd::bitand), ORI => self.binary_op_imm::(ops::BitOr::bitor), XORI => self.binary_op_imm::(ops::BitXor::bitxor), SLI => self.binary_op_ims(u64::wrapping_shl), SRI => self.binary_op_ims(u64::wrapping_shr), SRSI => self.binary_op_ims(i64::wrapping_shr), CMPI => { let ParamBBD(tg, a0, imm) = self.decode(); self.write_reg( tg, self.read_reg(a0) .cast::() .cmp(&Value::from(imm).cast::()) as i64, ); } CMPUI => { let ParamBBD(tg, a0, imm) = self.decode(); self.write_reg(tg, self.read_reg(a0).cast::().cmp(&imm) as i64); } CP => { let ParamBB(tg, a0) = self.decode(); self.write_reg(tg, self.read_reg(a0)); } SWA => { // Swap registers let ParamBB(r0, r1) = self.decode(); match (r0, r1) { (0, 0) => (), (dst, 0) | (0, dst) => self.write_reg(dst, 0_u64), (r0, r1) => { core::ptr::swap( self.registers.get_unchecked_mut(usize::from(r0)), self.registers.get_unchecked_mut(usize::from(r1)), ); } } } LI => { let ParamBD(tg, imm) = self.decode(); self.write_reg(tg, imm); } LD => { // Load. If loading more than register size, continue on adjecent registers let ParamBBDH(dst, base, off, count) = self.decode(); let n: usize = match dst { 0 => 1, _ => 0, }; self.memory.load( self.read_reg(base).cast::() + off + n as u64, self.registers.as_mut_ptr().add(usize::from(dst) + n).cast(), usize::from(count).saturating_sub(n), &mut self.pfhandler, )?; } ST => { // Store. Same rules apply as to LD let ParamBBDH(dst, base, off, count) = self.decode(); self.memory.store( self.read_reg(base).cast::() + off, self.registers.as_ptr().add(usize::from(dst)).cast(), count.into(), &mut self.pfhandler, )?; } BMC => { // Block memory copy let ParamBBD(src, dst, count) = self.decode(); self.memory.block_copy( self.read_reg(src).cast::(), self.read_reg(dst).cast::(), count as _, &mut self.pfhandler, )?; } BRC => { // Block register copy let ParamBBB(src, dst, count) = self.decode(); core::ptr::copy( self.registers.get_unchecked(usize::from(src)), self.registers.get_unchecked_mut(usize::from(dst)), usize::from(count), ); } JAL => { // Jump and link. Save PC after this instruction to // specified register and jump to reg + offset. let ParamBBD(save, reg, offset) = self.decode(); self.write_reg(save, self.pc as u64); self.pc = (self.read_reg(reg).cast::() + offset) as usize; } // Conditional jumps, jump only to immediates JEQ => self.cond_jmp::(Ordering::Equal), JNE => { let ParamBBD(a0, a1, jt) = self.decode(); if self.read_reg(a0).cast::() != self.read_reg(a1).cast::() { self.pc = jt as usize; } } JLT => self.cond_jmp::(Ordering::Less), JGT => self.cond_jmp::(Ordering::Greater), JLTU => self.cond_jmp::(Ordering::Less), JGTU => self.cond_jmp::(Ordering::Greater), ECALL => { self.decode::<()>(); // So we don't get timer interrupt after ECALL if TIMER_QUOTIENT != 0 { self.timer = self.timer.wrapping_add(1); } return Ok(VmRunOk::Ecall); } ADDF => self.binary_op::(ops::Add::add), SUBF => self.binary_op::(ops::Sub::sub), MULF => self.binary_op::(ops::Mul::mul), DIRF => { let ParamBBBB(dt, rt, a0, a1) = self.decode(); let a0 = self.read_reg(a0).cast::(); let a1 = self.read_reg(a1).cast::(); self.write_reg(dt, a0 / a1); self.write_reg(rt, a0 % a1); } FMAF => { let ParamBBBB(dt, a0, a1, a2) = self.decode(); self.write_reg( dt, self.read_reg(a0).cast::() * self.read_reg(a1).cast::() + self.read_reg(a2).cast::(), ); } NEGF => { let ParamBB(dt, a0) = self.decode(); self.write_reg(dt, -self.read_reg(a0).cast::()); } ITF => { let ParamBB(dt, a0) = self.decode(); self.write_reg(dt, self.read_reg(a0).cast::() as f64); } FTI => { let ParamBB(dt, a0) = self.decode(); self.write_reg(dt, self.read_reg(a0).cast::() as i64); } ADDFI => self.binary_op_imm::(ops::Add::add), MULFI => self.binary_op_imm::(ops::Mul::mul), op => return Err(VmRunError::InvalidOpcode(op)), } } if TIMER_QUOTIENT != 0 { self.timer = self.timer.wrapping_add(1); if self.timer % TIMER_QUOTIENT == 0 { return Ok(VmRunOk::Timer); } } } } /// Decode instruction operands #[inline] unsafe fn decode(&mut self) -> T { let data = self.program.as_ptr().add(self.pc + 1).cast::().read(); self.pc += 1 + core::mem::size_of::(); data } /// Perform binary operating over two registers #[inline] unsafe fn binary_op(&mut self, op: impl Fn(T, T) -> T) { let ParamBBB(tg, a0, a1) = self.decode(); self.write_reg( tg, op(self.read_reg(a0).cast::(), self.read_reg(a1).cast::()), ); } /// Perform binary operation over register and immediate #[inline] unsafe fn binary_op_imm(&mut self, op: impl Fn(T, T) -> T) { let ParamBBD(tg, reg, imm) = self.decode(); self.write_reg( tg, op(self.read_reg(reg).cast::(), Value::from(imm).cast::()), ); } /// Perform binary operation over register and shift immediate #[inline] unsafe fn binary_op_ims(&mut self, op: impl Fn(T, u32) -> T) { let ParamBBW(tg, reg, imm) = self.decode(); self.write_reg(tg, op(self.read_reg(reg).cast::(), imm)); } /// Jump at `#3` if ordering on `#0 <=> #1` is equal to expected #[inline] unsafe fn cond_jmp(&mut self, expected: Ordering) { let ParamBBD(a0, a1, ja) = self.decode(); if self .read_reg(a0) .cast::() .cmp(&self.read_reg(a1).cast::()) == expected { self.pc = ja as usize; } } /// Read register #[inline] unsafe fn read_reg(&self, n: u8) -> Value { *self.registers.get_unchecked(n as usize) } /// Write a register. /// Writing to register 0 is no-op. #[inline] unsafe fn write_reg(&mut self, n: u8, value: impl Into) { if n != 0 { *self.registers.get_unchecked_mut(n as usize) = value.into(); } } } /// Virtual machine halt error #[derive(Copy, Clone, Debug, PartialEq, Eq)] #[repr(u8)] pub enum VmRunError { /// Tried to execute invalid instruction InvalidOpcode(u8), /// Unhandled load access exception LoadAccessEx(u64), /// Unhandled store access exception StoreAccessEx(u64), /// Reached unreachable code Unreachable, } /// Virtual machine halt ok #[derive(Copy, Clone, Debug, PartialEq, Eq)] pub enum VmRunOk { /// Program has eached its end End, /// Program was interrupted by a timer Timer, /// Environment call Ecall, }