// Copyright 2024 Gabriel Bjørnager Jensen.
//
// This file is part of Pollex.
//
// Pollex is free software: you can redistribute it
// and/or modify it under the terms of the GNU Af-
// fero General Public License as published by the
// Free Software Foundation, either version 3 of
// the License, or (at your option) any later ver-
// sion.
//
// Pollex is distributed in the hope that it will
// be useful, but WITHOUT ANY WARRANTY; without
// even the implied warranty of MERCHANTABILITY or
// FITNESS FOR A PARTICULAR PURPOSE. See the GNU
// Affero General Public License for more details.
//
// You should have received a copy of the GNU Af-
// fero General Public License along with Pollex.
// If not, see <https://www.gnu.org/licenses/>.
use crate::{assert_or_err, Error, Result};
use crate::arm32::{
Instruction,
InstructionCodec,
Predicate,
Sflag,
Shifter,
ThumbOpcode,
};
use core::num::Wrapping;
macro_rules! quick_assert {
(base_equals_destination: $base:expr, $destination:expr) => {{
assert_or_err!($base == $destination, Error::IllegalRegister { reason: "base must also be destination on thumb" });
}};
(low_register: $register:expr) => {{
assert_or_err!($register.is_low(), Error::IllegalRegister { reason: "cannot encode low register on thumb" });
}};
(predicate_always: $predicate:expr) => {{
assert_or_err!($predicate == Predicate::Always, Error::IllegalPredicate { reason: "must be `AL` on thumb" });
}};
(s_flag_on: $flag:expr) => {{
assert_or_err!($flag.is_on(), Error::IllegalFlag { reason: "s flag must be on on thumb" });
}};
(source_equals_destination: $source:expr, $destination:expr) => {{
assert_or_err!($source == $destination, Error::IllegalRegister { reason: "source must also be destination on thumb" });
}};
}
#[inline]
const fn encode_shift_immediate(shift: u32) -> Result<u32> {
match shift {
0x0 => Err(Error::IllegalImmediate { reason: "immediate shifts cannot be null on thumb" }),
0x1..=0x1F => Ok(shift),
0x20 => Ok(0x0),
_ => Err(Error::IllegalImmediate { reason: "immediate shifts cannot be greater than (32) on thumb" }),
}
}
impl InstructionCodec {
/// Encodes the given Thumb instruction.
///
/// # Errors
///
/// If the given instruction cannot be encoded for Thumb, an error is returned.
pub fn encode_thumb(&mut self, instruction: Instruction) -> Result<(ThumbOpcode, Option<ThumbOpcode>)> {
use Instruction::*;
let mut opcode = (0b00000000_00000000_u16, 0b00000000_00000000_u16);
let mut has_opcode1 = false;
match instruction {
// Add {
// predicate,
// destination,
// base,
// source,
// s,
// } => {
//
// }
AddCarry {
predicate,
destination,
base,
source,
s,
} => {
let source = source.as_register()?;
quick_assert!(predicate_always: predicate);
quick_assert!(base_equals_destination: base, destination);
quick_assert!(low_register: destination);
quick_assert!(low_register: source);
quick_assert!(s_flag_on: s);
opcode.0 |= 0b01000001_01000000;
opcode.0 |= destination as u16;
opcode.0 |= (source as u16).wrapping_shl(0x3);
}
And {
predicate,
destination,
base,
source,
s,
} => {
let source = source.as_register()?;
quick_assert!(predicate_always: predicate);
quick_assert!(base_equals_destination: base, destination);
quick_assert!(low_register: destination);
quick_assert!(low_register: source);
quick_assert!(s_flag_on: s);
opcode.0 |= 0b01000000_00000000;
opcode.0 |= destination as u16;
opcode.0 |= (source as u16).wrapping_shl(0x3);
}
BitClear {
predicate,
destination,
base,
source,
s,
} => {
let source = source.as_register()?;
quick_assert!(predicate_always: predicate);
quick_assert!(base_equals_destination: base, destination);
quick_assert!(low_register: destination);
quick_assert!(low_register: source);
quick_assert!(s_flag_on: s);
opcode.0 |= 0b01000011_10000000;
opcode.0 |= destination as u16;
opcode.0 |= (source as u16).wrapping_shl(0x3);
}
Branch {
predicate,
immediate,
} => {
let offset = (Wrapping(immediate) - self.address - Wrapping(0x4)).0 as i32;
if predicate == Predicate::Always {
assert_or_err!(offset >= -0x800, Error::IllegalImmediate { reason: "cannot enocde offset larger than (-2048) on thumb" });
assert_or_err!(offset <= 0x7FE, Error::IllegalImmediate { reason: "cannot enocde offset larger than (2046) on thumb" });
let offset = offset as u32;
opcode.0 |= 0b11100000_00000000;
opcode.0 |= ((offset & 0b00001111_11111111).wrapping_shr(0x1)) as u16;
} else {
opcode.0 |= 0b11010000_00000000;
opcode.0 |= (predicate as u16).wrapping_shl(0x8);
opcode.0 |= ((offset & 0b00000001_11111111).wrapping_shr(0x1)) as u16;
}
}
BranchExchange {
predicate,
source,
} => {
quick_assert!(predicate_always: predicate);
opcode.0 |= 0b01000111_00000000;
opcode.0 |= (source as u16).wrapping_shl(0x3);
}
BranchLink {
predicate,
source,
} => {
quick_assert!(predicate_always: predicate);
let offset = (Wrapping(source) - self.address - Wrapping(0x4)).0 as i32;
assert_or_err!(offset >= -0x00400000, Error::IllegalImmediate { reason: "cannot encode offset larger than (-4194304) on thumb" });
assert_or_err!(offset <= 0x003FFFFE, Error::IllegalImmediate { reason: "cannot encode offset larger than (4194302) on thumb" });
assert_or_err!(offset % 0x2 == 0x0, Error::IllegalImmediate { reason: "cannot encode uneven offset on thumb" });
let offset = offset as u32;
opcode.0 |= 0b11110000_00000000;
opcode.0 |= ((offset & 0b00000000_00111111_11110000_00000000).wrapping_shr(0xC)) as u16;
opcode.1 |= 0b11111000_00000000;
opcode.1 |= ((offset & 0b00000000_00000000_00001111_11111110).wrapping_shr(0x1)) as u16;
has_opcode1 = true;
}
BranchLinkExchange {
predicate,
source,
} => {
quick_assert!(predicate_always: predicate);
let source = source.as_register()
.map_err(|_| Error::IllegalShifter { reason: "can only encode registers on thumb" })?;
opcode.0 |= 0b01000111_10000000;
opcode.0 |= (source as u16).wrapping_shl(0x3);
}
Breakpoint {
immediate,
} => {
assert_or_err!(immediate <= 0xFF, Error::IllegalImmediate { reason: "cannot encode larger than (255) on thumb" });
opcode.0 |= 0b10111110_00000000;
opcode.0 |= immediate as u16;
}
ExclusiveOr {
predicate,
destination,
base,
source,
s,
} => {
let source = source.as_register()?;
quick_assert!(predicate_always: predicate);
quick_assert!(base_equals_destination: base, destination);
quick_assert!(low_register: destination);
quick_assert!(low_register: source);
quick_assert!(s_flag_on: s);
opcode.0 |= 0b01000000_01000000;
opcode.0 |= destination as u16;
opcode.0 |= (source as u16).wrapping_shl(0x3);
}
InclusiveOr {
predicate,
destination,
base,
source,
s,
} => {
let source = source.as_register()?;
quick_assert!(predicate_always: predicate);
quick_assert!(base_equals_destination: base, destination);
quick_assert!(low_register: destination);
quick_assert!(low_register: source);
quick_assert!(s_flag_on: s);
opcode.0 |= 0b01000011_00000000;
opcode.0 |= destination as u16;
opcode.0 |= (source as u16).wrapping_shl(0x3);
}
Move {
predicate,
destination,
source: Shifter::ArithmeticShiftRightImmediate { source, shift },
s,
} => {
quick_assert!(predicate_always: predicate);
quick_assert!(source_equals_destination: source, destination);
quick_assert!(low_register: destination);
quick_assert!(low_register: source);
quick_assert!(s_flag_on: s);
let shift = encode_shift_immediate(shift)?;
opcode.0 |= 0b00010000_00000000;
opcode.0 |= destination as u16;
opcode.0 |= (source as u16).wrapping_shl(0x3);
opcode.0 |= (shift as u16).wrapping_shl(0x6);
}
Move {
predicate,
destination,
source: Shifter::ArithmeticShiftRightRegister { source, shift },
s,
} => {
quick_assert!(predicate_always: predicate);
quick_assert!(source_equals_destination: source, destination);
quick_assert!(low_register: destination);
quick_assert!(low_register: source);
quick_assert!(s_flag_on: s);
opcode.0 |= 0b01000001_00000000;
opcode.0 |= destination as u16;
opcode.0 |= (shift as u16).wrapping_shl(0x3);
}
Move {
predicate,
destination,
source: Shifter::LogicalShiftLeftImmediate { source, shift },
s,
} => {
quick_assert!(predicate_always: predicate);
quick_assert!(source_equals_destination: source, destination);
quick_assert!(low_register: destination);
quick_assert!(low_register: source);
quick_assert!(s_flag_on: s);
// Remember that LSL does takes null shifts.
assert_or_err!(shift <= 0x1F, Error::IllegalImmediate { reason: "shift must be at most (31)" });
opcode.0 |= destination as u16;
opcode.0 |= (source as u16).wrapping_shl(0x3);
opcode.0 |= (shift as u16).wrapping_shl(0x6);
}
Move {
predicate,
destination,
source: Shifter::LogicalShiftLeftRegister { source, shift },
s,
} => {
quick_assert!(predicate_always: predicate);
quick_assert!(source_equals_destination: source, destination);
quick_assert!(low_register: destination);
quick_assert!(low_register: source);
quick_assert!(s_flag_on: s);
opcode.0 |= 0b01000000_10000000;
opcode.0 |= destination as u16;
opcode.0 |= (shift as u16).wrapping_shl(0x3);
}
Move {
predicate,
destination,
source: Shifter::LogicalShiftRightImmediate { source, shift },
s,
} => {
quick_assert!(predicate_always: predicate);
quick_assert!(source_equals_destination: source, destination);
quick_assert!(low_register: destination);
quick_assert!(low_register: source);
quick_assert!(s_flag_on: s);
let shift = encode_shift_immediate(shift)?;
opcode.0 |= 0b00001000_00000000;
opcode.0 |= destination as u16;
opcode.0 |= (source as u16).wrapping_shl(0x3);
opcode.0 |= (shift as u16).wrapping_shl(0x6);
}
Move {
predicate,
destination,
source: Shifter::LogicalShiftRightRegister { source, shift },
s,
} => {
quick_assert!(predicate_always: predicate);
quick_assert!(source_equals_destination: source, destination);
quick_assert!(low_register: destination);
quick_assert!(low_register: source);
quick_assert!(s_flag_on: s);
opcode.0 |= 0b01000000_11000000;
opcode.0 |= destination as u16;
opcode.0 |= (shift as u16).wrapping_shl(0x3);
}
Move {
predicate,
destination,
source: Shifter::RotateRightRegister { source, shift },
s,
} => {
quick_assert!(predicate_always: predicate);
quick_assert!(source_equals_destination: source, destination);
quick_assert!(low_register: destination);
quick_assert!(low_register: source);
quick_assert!(s_flag_on: s);
opcode.0 |= 0b01000001_11000000;
opcode.0 |= destination as u16;
opcode.0 |= (shift as u16).wrapping_shl(0x3);
}
Move {
predicate,
destination,
source,
s: Sflag::Off,
} => {
quick_assert!(predicate_always: predicate);
if let Ok(source) = source.as_register() {
opcode.0 |= 0b01000110_00000000;
let h0 = destination.is_high();
let h1 = source.is_high();
opcode.0 |= destination as u16 & 0b00000000_00000111;
opcode.0 |= (source as u16 & 0b00000000_00000111).wrapping_shl(0x3);
opcode.0 |= u16::from(h0).wrapping_shl(0x6);
opcode.0 |= u16::from(h1).wrapping_shl(0x7);
} else {
return Err(Error::IllegalShifter { reason: "can only encode registers with s flag off" });
}
}
Move {
predicate,
destination,
source,
s: Sflag::On,
} => {
quick_assert!(predicate_always: predicate);
if let Shifter::Immediate(source) = source {
quick_assert!(low_register: destination);
assert_or_err!(source <= 0xFF, Error::IllegalImmediate { reason: "cannot encode larger than (255) on thumb" });
opcode.0 |= 0b00100000_00000000;
opcode.0 |= source as u16;
opcode.0 |= (destination as u16).wrapping_shl(0x8);
} else if let Ok(source) = source.as_register() {
quick_assert!(low_register: destination);
quick_assert!(low_register: source);
opcode.0 |= 0b00100000_00000000;
opcode.0 |= destination as u16;
opcode.0 |= (source as u16).wrapping_shl(0x3);
} else {
return Err(Error::IllegalShifter { reason: "not encodable on thumb" });
}
}
MoveNot {
predicate,
destination,
source,
s,
} => {
let source = source.as_register()?;
quick_assert!(predicate_always: predicate);
quick_assert!(low_register: destination);
quick_assert!(low_register: source);
quick_assert!(s_flag_on: s);
opcode.0 |= 0b01000011_11000000;
opcode.0 |= destination as u16;
opcode.0 |= (source as u16).wrapping_shl(0x3);
}
Multiply {
predicate,
destination,
base,
source,
s,
} => {
quick_assert!(predicate_always: predicate);
quick_assert!(base_equals_destination: base, destination);
quick_assert!(low_register: destination);
quick_assert!(low_register: source);
quick_assert!(s_flag_on: s);
opcode.0 |= 0b01000011_01000000;
opcode.0 |= destination as u16;
opcode.0 |= (source as u16).wrapping_shl(0x3);
}
SoftwareInterrupt {
predicate,
immediate,
} => {
quick_assert!(predicate_always: predicate);
assert_or_err!(immediate <= 0xFF, Error::IllegalImmediate { reason: "cannot encode larger than (255) on thumb" });
opcode.0 |= 0b11011111_00000000;
opcode.0 |= immediate as u16;
}
SubtractCarry {
predicate,
destination,
base,
source,
s,
} => {
let source = source.as_register()?;
quick_assert!(predicate_always: predicate);
quick_assert!(base_equals_destination: base, destination);
quick_assert!(low_register: destination);
quick_assert!(low_register: source);
quick_assert!(s_flag_on: s);
opcode.0 |= 0b01000000_11000000;
opcode.0 |= destination as u16;
opcode.0 |= (source as u16).wrapping_shl(0x3);
}
_ => return Err(Error::IllegalInstruction { reason: "not supported on thumb" } ),
}
let opcode_count = 0x1 + u32::from(has_opcode1);
self.skip_halfwords(opcode_count);
Ok((opcode.0.into(), has_opcode1.then_some(opcode.1.into())))
}
}
