revm_interpreter/interpreter/
stack.rs

1use crate::InstructionResult;
2use core::{fmt, ptr};
3use primitives::U256;
4use std::vec::Vec;
5
6use super::StackTr;
7
8/// EVM interpreter stack limit.
9pub const STACK_LIMIT: usize = 1024;
10
11/// EVM stack with [STACK_LIMIT] capacity of words.
12#[derive(Debug, PartialEq, Eq, Hash)]
13#[cfg_attr(feature = "serde", derive(serde::Serialize))]
14pub struct Stack {
15    /// The underlying data of the stack.
16    data: Vec<U256>,
17}
18
19impl fmt::Display for Stack {
20    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
21        f.write_str("[")?;
22        for (i, x) in self.data.iter().enumerate() {
23            if i > 0 {
24                f.write_str(", ")?;
25            }
26            write!(f, "{x}")?;
27        }
28        f.write_str("]")
29    }
30}
31
32impl Default for Stack {
33    #[inline]
34    fn default() -> Self {
35        Self::new()
36    }
37}
38
39impl Clone for Stack {
40    fn clone(&self) -> Self {
41        // Use `Self::new()` to ensure the cloned Stack is constructed with at least
42        // STACK_LIMIT capacity, and then copy the data. This preserves the invariant
43        // that Stack has sufficient capacity for operations that rely on it.
44        let mut new_stack = Self::new();
45        new_stack.data.extend_from_slice(&self.data);
46        new_stack
47    }
48}
49
50impl StackTr for Stack {
51    #[inline]
52    fn len(&self) -> usize {
53        self.len()
54    }
55
56    #[inline]
57    fn data(&self) -> &[U256] {
58        &self.data
59    }
60
61    #[inline]
62    fn clear(&mut self) {
63        self.data.clear();
64    }
65
66    #[inline]
67    fn popn<const N: usize>(&mut self) -> Option<[U256; N]> {
68        if self.len() < N {
69            return None;
70        }
71        // SAFETY: Stack length is checked above.
72        Some(unsafe { self.popn::<N>() })
73    }
74
75    #[inline]
76    fn popn_top<const POPN: usize>(&mut self) -> Option<([U256; POPN], &mut U256)> {
77        if self.len() < POPN + 1 {
78            return None;
79        }
80        // SAFETY: Stack length is checked above.
81        Some(unsafe { self.popn_top::<POPN>() })
82    }
83
84    #[inline]
85    fn exchange(&mut self, n: usize, m: usize) -> bool {
86        self.exchange(n, m)
87    }
88
89    #[inline]
90    fn dup(&mut self, n: usize) -> bool {
91        self.dup(n)
92    }
93
94    #[inline]
95    fn push(&mut self, value: U256) -> bool {
96        self.push(value)
97    }
98
99    #[inline]
100    fn push_slice(&mut self, slice: &[u8]) -> bool {
101        self.push_slice_(slice)
102    }
103}
104
105impl Stack {
106    /// Instantiate a new stack with the [default stack limit][STACK_LIMIT].
107    #[inline]
108    pub fn new() -> Self {
109        Self {
110            // SAFETY: Expansion functions assume that capacity is `STACK_LIMIT`.
111            data: Vec::with_capacity(STACK_LIMIT),
112        }
113    }
114
115    /// Instantiate a new invalid Stack.
116    #[inline]
117    pub fn invalid() -> Self {
118        Self { data: Vec::new() }
119    }
120
121    /// Returns the length of the stack in words.
122    #[inline]
123    pub fn len(&self) -> usize {
124        self.data.len()
125    }
126
127    /// Returns whether the stack is empty.
128    #[inline]
129    pub fn is_empty(&self) -> bool {
130        self.data.is_empty()
131    }
132
133    /// Returns a reference to the underlying data buffer.
134    #[inline]
135    pub fn data(&self) -> &Vec<U256> {
136        &self.data
137    }
138
139    /// Returns a mutable reference to the underlying data buffer.
140    #[inline]
141    pub fn data_mut(&mut self) -> &mut Vec<U256> {
142        &mut self.data
143    }
144
145    /// Consumes the stack and returns the underlying data buffer.
146    #[inline]
147    pub fn into_data(self) -> Vec<U256> {
148        self.data
149    }
150
151    /// Removes the topmost element from the stack and returns it, or `StackUnderflow` if it is
152    /// empty.
153    #[inline]
154    #[cfg_attr(debug_assertions, track_caller)]
155    pub fn pop(&mut self) -> Result<U256, InstructionResult> {
156        self.data.pop().ok_or(InstructionResult::StackUnderflow)
157    }
158
159    /// Removes the topmost element from the stack and returns it.
160    ///
161    /// # Safety
162    ///
163    /// The caller is responsible for checking the length of the stack.
164    #[inline]
165    #[cfg_attr(debug_assertions, track_caller)]
166    pub unsafe fn pop_unsafe(&mut self) -> U256 {
167        assume!(!self.data.is_empty());
168        self.data.pop().unwrap_unchecked()
169    }
170
171    /// Peeks the top of the stack.
172    ///
173    /// # Safety
174    ///
175    /// The caller is responsible for checking the length of the stack.
176    #[inline]
177    #[cfg_attr(debug_assertions, track_caller)]
178    pub unsafe fn top_unsafe(&mut self) -> &mut U256 {
179        assume!(!self.data.is_empty());
180        self.data.last_mut().unwrap_unchecked()
181    }
182
183    /// Pops `N` values from the stack.
184    ///
185    /// # Safety
186    ///
187    /// The caller is responsible for checking the length of the stack.
188    #[inline]
189    #[cfg_attr(debug_assertions, track_caller)]
190    pub unsafe fn popn<const N: usize>(&mut self) -> [U256; N] {
191        assume!(self.data.len() >= N);
192        core::array::from_fn(|_| unsafe { self.pop_unsafe() })
193    }
194
195    /// Pops `N` values from the stack and returns the top of the stack.
196    ///
197    /// # Safety
198    ///
199    /// The caller is responsible for checking the length of the stack.
200    #[inline]
201    #[cfg_attr(debug_assertions, track_caller)]
202    pub unsafe fn popn_top<const POPN: usize>(&mut self) -> ([U256; POPN], &mut U256) {
203        let result = self.popn::<POPN>();
204        let top = self.top_unsafe();
205        (result, top)
206    }
207
208    /// Push a new value onto the stack.
209    ///
210    /// If it will exceed the stack limit, returns false and leaves the stack
211    /// unchanged.
212    #[inline]
213    #[must_use]
214    #[cfg_attr(debug_assertions, track_caller)]
215    pub fn push(&mut self, value: U256) -> bool {
216        // In debug builds, verify we have sufficient capacity provisioned.
217        debug_assert!(self.data.capacity() >= STACK_LIMIT);
218        if self.data.len() == STACK_LIMIT {
219            return false;
220        }
221        self.data.push(value);
222        true
223    }
224
225    /// Peek a value at given index for the stack, where the top of
226    /// the stack is at index `0`. If the index is too large,
227    /// `StackError::Underflow` is returned.
228    #[inline]
229    pub fn peek(&self, no_from_top: usize) -> Result<U256, InstructionResult> {
230        if self.data.len() > no_from_top {
231            Ok(self.data[self.data.len() - no_from_top - 1])
232        } else {
233            Err(InstructionResult::StackUnderflow)
234        }
235    }
236
237    /// Duplicates the `N`th value from the top of the stack.
238    ///
239    /// # Panics
240    ///
241    /// Panics if `n` is 0.
242    #[inline]
243    #[must_use]
244    #[cfg_attr(debug_assertions, track_caller)]
245    pub fn dup(&mut self, n: usize) -> bool {
246        assume!(n > 0, "attempted to dup 0");
247        let len = self.data.len();
248        if len < n || len + 1 > STACK_LIMIT {
249            false
250        } else {
251            // SAFETY: Check for out of bounds is done above and it makes this safe to do.
252            unsafe {
253                let ptr = self.data.as_mut_ptr().add(len);
254                ptr::copy_nonoverlapping(ptr.sub(n), ptr, 1);
255                self.data.set_len(len + 1);
256            }
257            true
258        }
259    }
260
261    /// Swaps the topmost value with the `N`th value from the top.
262    ///
263    /// # Panics
264    ///
265    /// Panics if `n` is 0.
266    #[inline(always)]
267    #[cfg_attr(debug_assertions, track_caller)]
268    pub fn swap(&mut self, n: usize) -> bool {
269        self.exchange(0, n)
270    }
271
272    /// Exchange two values on the stack.
273    ///
274    /// `n` is the first index, and the second index is calculated as `n + m`.
275    ///
276    /// # Panics
277    ///
278    /// Panics if `m` is zero.
279    #[inline]
280    #[cfg_attr(debug_assertions, track_caller)]
281    pub fn exchange(&mut self, n: usize, m: usize) -> bool {
282        assume!(m > 0, "overlapping exchange");
283        let len = self.data.len();
284        let n_m_index = n + m;
285        if n_m_index >= len {
286            return false;
287        }
288        // SAFETY: `n` and `n_m` are checked to be within bounds, and they don't overlap.
289        unsafe {
290            // Note: `ptr::swap_nonoverlapping` is more efficient than `slice::swap` or `ptr::swap`
291            // because it operates under the assumption that the pointers do not overlap,
292            // eliminating an intermediate copy,
293            // which is a condition we know to be true in this context.
294            let top = self.data.as_mut_ptr().add(len - 1);
295            core::ptr::swap_nonoverlapping(top.sub(n), top.sub(n_m_index), 1);
296        }
297        true
298    }
299
300    /// Pushes an arbitrary length slice of bytes onto the stack, padding the last word with zeros
301    /// if necessary.
302    #[inline]
303    pub fn push_slice(&mut self, slice: &[u8]) -> Result<(), InstructionResult> {
304        if self.push_slice_(slice) {
305            Ok(())
306        } else {
307            Err(InstructionResult::StackOverflow)
308        }
309    }
310
311    /// Pushes an arbitrary length slice of bytes onto the stack, padding the last word with zeros
312    /// if necessary.
313    #[inline]
314    fn push_slice_(&mut self, slice: &[u8]) -> bool {
315        if slice.is_empty() {
316            return true;
317        }
318
319        let n_words = slice.len().div_ceil(32);
320        let new_len = self.data.len() + n_words;
321        if new_len > STACK_LIMIT {
322            return false;
323        }
324
325        // In debug builds, ensure underlying capacity is sufficient for the write.
326        debug_assert!(self.data.capacity() >= new_len);
327
328        // SAFETY: Length checked above.
329        unsafe {
330            let dst = self.data.as_mut_ptr().add(self.data.len()).cast::<u64>();
331            self.data.set_len(new_len);
332
333            let mut i = 0;
334
335            // Write full words
336            let words = slice.chunks_exact(32);
337            let partial_last_word = words.remainder();
338            for word in words {
339                // Note: We unroll `U256::from_be_bytes` here to write directly into the buffer,
340                // instead of creating a 32 byte array on the stack and then copying it over.
341                for l in word.rchunks_exact(8) {
342                    dst.add(i).write(u64::from_be_bytes(l.try_into().unwrap()));
343                    i += 1;
344                }
345            }
346
347            if partial_last_word.is_empty() {
348                return true;
349            }
350
351            // Write limbs of partial last word
352            let limbs = partial_last_word.rchunks_exact(8);
353            let partial_last_limb = limbs.remainder();
354            for l in limbs {
355                dst.add(i).write(u64::from_be_bytes(l.try_into().unwrap()));
356                i += 1;
357            }
358
359            // Write partial last limb by padding with zeros
360            if !partial_last_limb.is_empty() {
361                let mut tmp = [0u8; 8];
362                tmp[8 - partial_last_limb.len()..].copy_from_slice(partial_last_limb);
363                dst.add(i).write(u64::from_be_bytes(tmp));
364                i += 1;
365            }
366
367            debug_assert_eq!(i.div_ceil(4), n_words, "wrote too much");
368
369            // Zero out upper bytes of last word
370            let m = i % 4; // 32 / 8
371            if m != 0 {
372                dst.add(i).write_bytes(0, 4 - m);
373            }
374        }
375
376        true
377    }
378
379    /// Set a value at given index for the stack, where the top of the
380    /// stack is at index `0`. If the index is too large,
381    /// `StackError::Underflow` is returned.
382    #[inline]
383    pub fn set(&mut self, no_from_top: usize, val: U256) -> Result<(), InstructionResult> {
384        if self.data.len() > no_from_top {
385            let len = self.data.len();
386            self.data[len - no_from_top - 1] = val;
387            Ok(())
388        } else {
389            Err(InstructionResult::StackUnderflow)
390        }
391    }
392}
393
394#[cfg(feature = "serde")]
395impl<'de> serde::Deserialize<'de> for Stack {
396    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
397    where
398        D: serde::Deserializer<'de>,
399    {
400        let mut data = Vec::<U256>::deserialize(deserializer)?;
401        if data.len() > STACK_LIMIT {
402            return Err(serde::de::Error::custom(std::format!(
403                "stack size exceeds limit: {} > {}",
404                data.len(),
405                STACK_LIMIT
406            )));
407        }
408        data.reserve(STACK_LIMIT - data.len());
409        Ok(Self { data })
410    }
411}
412
413#[cfg(test)]
414mod tests {
415    use super::*;
416
417    fn run(f: impl FnOnce(&mut Stack)) {
418        let mut stack = Stack::new();
419        // Fill capacity with non-zero values
420        unsafe {
421            stack.data.set_len(STACK_LIMIT);
422            stack.data.fill(U256::MAX);
423            stack.data.set_len(0);
424        }
425        f(&mut stack);
426    }
427
428    #[test]
429    fn push_slices() {
430        // No-op
431        run(|stack| {
432            stack.push_slice(b"").unwrap();
433            assert!(stack.data.is_empty());
434        });
435
436        // One word
437        run(|stack| {
438            stack.push_slice(&[42]).unwrap();
439            assert_eq!(stack.data, [U256::from(42)]);
440        });
441
442        let n = 0x1111_2222_3333_4444_5555_6666_7777_8888_u128;
443        run(|stack| {
444            stack.push_slice(&n.to_be_bytes()).unwrap();
445            assert_eq!(stack.data, [U256::from(n)]);
446        });
447
448        // More than one word
449        run(|stack| {
450            let b = [U256::from(n).to_be_bytes::<32>(); 2].concat();
451            stack.push_slice(&b).unwrap();
452            assert_eq!(stack.data, [U256::from(n); 2]);
453        });
454
455        run(|stack| {
456            let b = [&[0; 32][..], &[42u8]].concat();
457            stack.push_slice(&b).unwrap();
458            assert_eq!(stack.data, [U256::ZERO, U256::from(42)]);
459        });
460
461        run(|stack| {
462            let b = [&[0; 32][..], &n.to_be_bytes()].concat();
463            stack.push_slice(&b).unwrap();
464            assert_eq!(stack.data, [U256::ZERO, U256::from(n)]);
465        });
466
467        run(|stack| {
468            let b = [&[0; 64][..], &n.to_be_bytes()].concat();
469            stack.push_slice(&b).unwrap();
470            assert_eq!(stack.data, [U256::ZERO, U256::ZERO, U256::from(n)]);
471        });
472    }
473
474    #[test]
475    fn stack_clone() {
476        // Test cloning an empty stack
477        let empty_stack = Stack::new();
478        let cloned_empty = empty_stack.clone();
479        assert_eq!(empty_stack, cloned_empty);
480        assert_eq!(cloned_empty.len(), 0);
481        assert_eq!(cloned_empty.data().capacity(), STACK_LIMIT);
482
483        // Test cloning a partially filled stack
484        let mut partial_stack = Stack::new();
485        for i in 0..10 {
486            assert!(partial_stack.push(U256::from(i)));
487        }
488        let mut cloned_partial = partial_stack.clone();
489        assert_eq!(partial_stack, cloned_partial);
490        assert_eq!(cloned_partial.len(), 10);
491        assert_eq!(cloned_partial.data().capacity(), STACK_LIMIT);
492
493        // Test that modifying the clone doesn't affect the original
494        assert!(cloned_partial.push(U256::from(100)));
495        assert_ne!(partial_stack, cloned_partial);
496        assert_eq!(partial_stack.len(), 10);
497        assert_eq!(cloned_partial.len(), 11);
498
499        // Test cloning a full stack
500        let mut full_stack = Stack::new();
501        for i in 0..STACK_LIMIT {
502            assert!(full_stack.push(U256::from(i)));
503        }
504        let mut cloned_full = full_stack.clone();
505        assert_eq!(full_stack, cloned_full);
506        assert_eq!(cloned_full.len(), STACK_LIMIT);
507        assert_eq!(cloned_full.data().capacity(), STACK_LIMIT);
508
509        // Test push to the full original or cloned stack should return StackOverflow
510        assert!(!full_stack.push(U256::from(100)));
511        assert!(!cloned_full.push(U256::from(100)));
512    }
513}
revm_interpreter/interpreter/stack.rs

revm_interpreter/interpreter/
stack.rs
