A

README.md

@@ -6,9 +6,9 @@ A small RISC-V emulator written in Rust.
 
 - [x] Base RV32I instruction set
 - [x] M standard extension
-- [ ] A standard extension
-    - [ ] Zalrsc standard extension
-    - [ ] Zaamo standard extension
+- [x] A standard extension
+    - [x] Zalrsc standard extension
+    - [x] Zaamo standard extension
 - [ ] F standard extension
 - [ ] D standard extension
 - [ ] C standard extension

src/emu.rs

@@ -1,4 +1,4 @@
-use crate::inst::{Inst, InstCode};
+use crate::inst::{AmoOp, Inst, InstCode};
 use std::{
     fmt::{Debug, Display},
     ops::{Index, IndexMut},
@@ -82,6 +82,9 @@ pub struct Emulator {
     /// Written to insterad of xreg[0].
     pub xreg0_value: u32,
     pub pc: u32,
+    /// We need to store the most recent reservation set for LR/SC
+    /// to make SC fail if it's not to this address.
+    pub reservation_set: Option<u32>,
 
     pub debug: bool,
 
@@ -356,6 +359,52 @@ impl Emulator {
                     self[dest] = self[src1] % self[src2];
                 }
             }
+            Inst::AmoW {
+                order: _,
+                op,
+                dest,
+                addr,
+                src,
+            } => {
+                let addr = self[addr];
+                self[dest] = self.mem.load_u32(addr)?;
+                let result = match op {
+                    AmoOp::Swap => self[src],
+                    AmoOp::Add => self[dest].wrapping_add(self[src]),
+                    AmoOp::Xor => self[dest] ^ self[src],
+                    AmoOp::And => self[dest] & self[src],
+                    AmoOp::Or => self[dest] | self[src],
+                    AmoOp::Min => (self[dest] as i32).min(self[src] as i32) as u32,
+                    AmoOp::Max => (self[dest] as i32).max(self[src] as i32) as u32,
+                    AmoOp::Minu => self[dest].min(self[src]),
+                    AmoOp::Maxu => self[dest].max(self[src]),
+                };
+                self.mem.store_u32(addr, result)?;
+            }
+            Inst::LrW {
+                order: _,
+                dest,
+                addr,
+            } => {
+                let addr = self[addr];
+                self[dest] = self.mem.load_u32(addr)?;
+                self.reservation_set = Some(addr);
+            }
+            Inst::ScW {
+                order: _,
+                dest,
+                addr,
+                src,
+            } => {
+                let addr = self[addr];
+                self.mem.store_u32(addr, self[src])?;
+                if self.reservation_set != Some(addr) {
+                    self[dest] = 1; // error
+                } else {
+                    self[dest] = 0; // success
+                }
+                self.reservation_set = None;
+            }
         }
 
         if !jumped {

src/inst.rs

@@ -3,6 +3,7 @@ use std::fmt::{Debug, Display};
 use std::ops::RangeInclusive;
 
 #[derive(Clone, Copy)]
+#[rustfmt::skip]
 pub enum Inst {
     Lui { uimm: u32, dest: Reg },
     Auipc { uimm: u32, dest: Reg },
@@ -62,6 +63,26 @@ pub enum Inst {
     Divu { dest: Reg, src1: Reg, src2: Reg },
     Rem { dest: Reg, src1: Reg, src2: Reg },
     Remu { dest: Reg, src1: Reg, src2: Reg },
+
+    // A
+    LrW {
+        order: AmoOrdering,
+        dest: Reg,
+        addr: Reg,  
+    },
+    ScW {
+        order: AmoOrdering,
+        dest: Reg,
+        addr: Reg,
+        src: Reg,
+    },
+    AmoW {
+        order: AmoOrdering,
+        op: AmoOp,
+        dest: Reg,
+        addr: Reg,
+        src: Reg,
+    },
 }
 
 #[derive(Clone, Copy)]
@@ -81,6 +102,27 @@ pub struct FenceSet {
     pub memory_write: bool,
 }
 
+#[derive(Clone, Copy)]
+pub enum AmoOrdering {
+    Relaxed,
+    Acquire,
+    Release,
+    SeqCst,
+}
+
+#[derive(Clone, Copy)]
+pub enum AmoOp {
+    Swap,
+    Add,
+    Xor,
+    And,
+    Or,
+    Min,
+    Max,
+    Minu,
+    Maxu,
+}
+
 impl Fence {
     pub fn is_pause(&self) -> bool {
         self.pred
@@ -102,11 +144,23 @@ impl Fence {
     }
 }
 
+impl AmoOrdering {
+    pub fn from_ac_rl(ac: bool, rl: bool) -> Self {
+        match (ac, rl) {
+            (false, false) => Self::Relaxed,
+            (true, false) => Self::Acquire,
+            (false, true) => Self::Release,
+            (true, true) => Self::SeqCst,
+        }
+    }
+}
+
 impl Debug for Inst {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         Display::fmt(&self, f)
     }
 }
+
 impl Display for Inst {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         match *self {
@@ -220,6 +274,20 @@ impl Display for Inst {
             Inst::Divu { dest, src1, src2 } => write!(f, "divu {dest}, {src1}, {src2}"),
             Inst::Rem { dest, src1, src2 } => write!(f, "rem {dest}, {src1}, {src2}"),
             Inst::Remu { dest, src1, src2 } => write!(f, "remu {dest}, {src1}, {src2}"),
+            Inst::LrW { order, dest, addr } => write!(f, "lr.w{order} {dest}, ({addr})",),
+            Inst::ScW {
+                order,
+                dest,
+                addr,
+                src,
+            } => write!(f, "sc.w{order} {dest}, {src}, ({addr})"),
+            Inst::AmoW {
+                order,
+                op,
+                dest,
+                addr,
+                src,
+            } => write!(f, "am{op}.w{order} {dest}, {src}, ({addr})",),
         }
     }
 }
@@ -242,6 +310,33 @@ impl Display for FenceSet {
     }
 }
 
+impl Display for AmoOrdering {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            AmoOrdering::Relaxed => write!(f, ""),
+            AmoOrdering::Acquire => write!(f, ".ac"),
+            AmoOrdering::Release => write!(f, ".rl"),
+            AmoOrdering::SeqCst => write!(f, ".acrl"),
+        }
+    }
+}
+
+impl Display for AmoOp {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            AmoOp::Swap => write!(f, "swap"),
+            AmoOp::Add => write!(f, "add"),
+            AmoOp::Xor => write!(f, "xor"),
+            AmoOp::And => write!(f, "and"),
+            AmoOp::Or => write!(f, "or"),
+            AmoOp::Min => write!(f, "min"),
+            AmoOp::Max => write!(f, "max"),
+            AmoOp::Minu => write!(f, "minu"),
+            AmoOp::Maxu => write!(f, "maxu"),
+        }
+    }
+}
+
 fn sign_extend(value: u32, size: u32) -> u32 {
     assert!(size <= u32::BITS);
     let sign = value >> (size - 1);
@@ -554,6 +649,62 @@ impl Inst {
                     _ => return Err(Error::IllegalInstruction(code, "imm")),
                 }
             }
+            // AMO
+            00101111 => {
+                // width must be W
+                if code.funct3() != 0b010 {
+                    return Err(Error::IllegalInstruction(code, "funct3"));
+                }
+
+                let kind = code.extract(27..=31);
+                let ac = code.extract(26..=26) == 1;
+                let rl = code.extract(25..=25) == 1;
+
+                let order = AmoOrdering::from_ac_rl(ac, rl);
+
+                match kind {
+                    // LR
+                    0b00010 => {
+                        if code.rs2().0 != 0 {
+                            return Err(Error::IllegalInstruction(code, "rs2"));
+                        }
+
+                        Inst::LrW {
+                            order,
+                            dest: code.rd(),
+                            addr: code.rs1(),
+                        }
+                    }
+                    // SC
+                    0b00011 => Inst::ScW {
+                        order,
+                        dest: code.rd(),
+                        addr: code.rs1(),
+                        src: code.rs2(),
+                    },
+                    _ => {
+                        let op = match kind {
+                            0b00001 => AmoOp::Swap,
+                            0b00000 => AmoOp::Add,
+                            0b00100 => AmoOp::Xor,
+                            0b01100 => AmoOp::And,
+                            0b01000 => AmoOp::Or,
+                            0b10000 => AmoOp::Min,
+                            0b10100 => AmoOp::Max,
+                            0b11000 => AmoOp::Minu,
+                            0b11100 => AmoOp::Maxu,
+                            _ => return Err(Error::IllegalInstruction(code, "funct7")),
+                        };
+                        Inst::AmoW {
+                            order,
+                            op,
+                            dest: code.rd(),
+                            addr: code.rs1(),
+                            src: code.rs2(),
+                        }
+                    }
+                }
+            }
             _ => return Err(Error::IllegalInstruction(code, "opcode")),
         };
         Ok(inst)

src/main.rs

@@ -64,6 +64,7 @@ fn main() -> eyre::Result<()> {
         xreg: [0; 32],
         xreg0_value: 0,
         pc: start,
+        reservation_set: None,
 
         debug: std::env::args().any(|arg| arg == "--debug"),
 

test/init1.rs

@@ -98,6 +98,9 @@ fn input() -> u64 {
 fn _start() -> ! {
     let random_number = 45;
 
+    let num = core::sync::atomic::AtomicI32::new(0);
+    num.swap(10, core::sync::atomic::Ordering::SeqCst);
+
     loop {
         let n = input();
         if n == random_number {