1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
use crate::evm::{
code_iterator::{CodeOp, iterate_code},
op,
};
#[derive(Debug, Clone, Eq, PartialEq, Hash)]
/// A symbolic value on the stack.
pub enum StackSym {
Before(usize),
Pushed([u8; 4]), // only PUSH[1..4] handled
Jumpdest(usize /*to*/),
Other(usize /*pc*/),
}
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub struct State {
stack: Vec<StackSym>,
}
impl State {
pub fn new() -> Self {
let mut stack = Vec::with_capacity(16);
stack.push(StackSym::Before(0));
Self { stack }
}
/// Builds an "identity" entry stack where deeper untouched slots stay addressable as
/// `Before(n)` after execution. This is used when replaying cached parent paths that need
/// more stack context than the minimal summary kept during the first resolution pass.
pub(crate) fn with_identity(depth: usize) -> Self {
Self {
stack: (0..=depth).rev().map(StackSym::Before).collect(),
}
}
pub(crate) fn explicit_len(&self) -> usize {
self.stack.len()
}
pub(crate) fn max_before(&self) -> Option<usize> {
self.stack
.iter()
.filter_map(|sym| match sym {
StackSym::Before(idx) => Some(*idx),
_ => None,
})
.max()
}
/// Returns the symbol at the given stack position (0 is the top of the stack)
/// If `pos` is beyond the current stack, a new `Before` symbol is synthesized
pub fn get_stack(&self, pos: usize) -> StackSym {
let slen = self.stack.len();
if pos < slen {
self.stack[slen - pos - 1].clone()
} else if let StackSym::Before(b) = self.stack[0] {
StackSym::Before(b + 1 + (pos - slen))
} else {
panic!("first stack element is not Before: {:?}", self.stack);
}
}
/// Resolves this state using a parent state.
///
/// This function "updates" the current state's 'Before' symbols using the parent's stack
pub fn resolve_with_parent(&self, parent: &State) -> State {
let base_before = if let StackSym::Before(v) = self.stack[0] {
v
} else {
panic!("first stack element is not Before: {:?}", self.stack);
};
let parent_len = parent.stack.len();
let extra = if parent_len > base_before {
parent_len - base_before - 1
} else {
0
};
let mut new_stack = Vec::with_capacity(self.stack.len() + extra);
if parent_len > base_before {
new_stack.extend_from_slice(&parent.stack[..(parent_len - base_before - 1)]);
}
// Replace every Before(i) symbol in self with the parent's corresponding stack symbol
new_stack.extend(self.stack.iter().map(|el| match el {
StackSym::Before(idx) => parent.get_stack(*idx),
other => other.clone(),
}));
State { stack: new_stack }
}
/// Executes the given code starting at 'start' and updates the state
///
/// After execution, the state's stack is "minimalized" by trimming redundant 'Before' symbols
pub fn exec(&mut self, code: &[u8], start: usize, end: Option<usize>) -> Option<StackSym> {
assert!(matches!(self.stack.first(), Some(StackSym::Before(_))));
let r = self.real_exec(code, start, end);
assert!(matches!(self.stack.first(), Some(StackSym::Before(_))));
// Before(4),Before(3),Before(2),Before(0) => Before(2),Before(0)
let base_before = if let StackSym::Before(v) = self.stack[0] {
v
} else {
panic!("first stack element is not Before: {:?}", self.stack);
};
let prefix_len = self
.stack
.iter()
.enumerate()
.take_while(|(pos, el)| matches!(el, StackSym::Before(nb) if *nb + pos == base_before))
.count();
if prefix_len > 1 {
self.stack.drain(..prefix_len - 1);
}
r
}
fn real_exec(
&mut self,
code: &[u8],
start_pc: usize,
end_pc: Option<usize>,
) -> Option<StackSym> {
for (pc, CodeOp { op, opi, .. }) in iterate_code(code, start_pc, end_pc) {
// eprintln!("{} | {:?}", pc, opi);
// Ensure the stack has at least (stack_in + 1) entries (the extra one preserves the initial Before)
if self.stack.len() < opi.stack_in + 1 {
let needed = opi.stack_in + 1 - self.stack.len();
if let StackSym::Before(base_before) = self.stack[0] {
self.stack.splice(
0..0,
((base_before + 1)..(base_before + 1 + needed))
.rev()
.map(StackSym::Before),
);
} else {
panic!(
"Expected first stack element to be Before: {:?}",
self.stack
)
};
}
match op {
op::PUSH1..=op::PUSH4 => {
let n = (op - op::PUSH0) as usize;
let mut args = [0u8; 4];
args[4 - n..].copy_from_slice(&code[pc + 1..pc + 1 + n]);
let val = u32::from_be_bytes(args) as usize;
self.stack
.push(if val < code.len() && code[val] == op::JUMPDEST {
StackSym::Jumpdest(val)
} else {
StackSym::Pushed(args)
});
}
op::DUP1..=op::DUP16 => {
let n = (op - op::DUP1 + 1) as usize;
let stack_len = self.stack.len();
self.stack.push(self.stack[stack_len - n].clone());
}
op::SWAP1..=op::SWAP16 => {
let n = (op - op::SWAP1 + 1) as usize;
let stack_len = self.stack.len();
self.stack.swap(stack_len - 1, stack_len - 1 - n);
}
op::AND => {
let s1 = self.stack.pop().expect("Stack underflow in AND");
let s2 = self.stack.pop().expect("Stack underflow in AND");
if s1 == StackSym::Pushed([0xff; 4]) {
self.stack.push(s2);
} else if s2 == StackSym::Pushed([0xff; 4]) {
self.stack.push(s1);
} else {
self.stack.push(StackSym::Other(pc));
}
}
op::JUMP => {
let to = self.stack.pop();
assert!(to.is_some());
return to; // already Some()
}
op::JUMPI => {
let to = self.stack.pop();
assert!(to.is_some());
self.stack.pop(); // condition
return to; // already Some()
}
op::JUMPDEST => {
// If we hit a JUMPDEST not at the start of our block, return
if pc != start_pc {
return None;
}
}
op::REVERT | op::RETURN | op::STOP | op::SELFDESTRUCT | op::INVALID => {
for _ in 0..opi.stack_in {
self.stack.pop();
}
for _ in 0..opi.stack_out {
self.stack.push(StackSym::Other(pc));
}
return None;
}
_ => {
for _ in 0..opi.stack_in {
self.stack.pop();
}
for _ in 0..opi.stack_out {
self.stack.push(StackSym::Other(pc));
}
}
}
}
None
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_prefix_drain() {
let cases = vec![
(
vec![
StackSym::Before(10),
StackSym::Before(5),
StackSym::Other(999),
],
vec![
StackSym::Before(10),
StackSym::Before(5),
StackSym::Other(999),
],
),
(
vec![
StackSym::Before(10),
StackSym::Before(9),
StackSym::Before(8),
StackSym::Other(999),
],
vec![StackSym::Before(8), StackSym::Other(999)],
),
(
vec![
StackSym::Before(10),
StackSym::Before(9),
StackSym::Before(8),
],
vec![StackSym::Before(8)],
),
(
vec![
StackSym::Before(3),
StackSym::Before(2),
StackSym::Before(3),
StackSym::Other(999),
],
vec![
StackSym::Before(2),
StackSym::Before(3),
StackSym::Other(999),
],
),
(
vec![
StackSym::Before(3),
StackSym::Before(2),
StackSym::Before(0),
StackSym::Before(1),
],
vec![
StackSym::Before(2),
StackSym::Before(0),
StackSym::Before(1),
],
),
(vec![StackSym::Before(0)], vec![StackSym::Before(0)]),
];
for (input_stack, expected_output_stack) in cases.into_iter() {
let mut state = State::new();
state.stack = input_stack;
state.exec(&[], 0, None);
assert_eq!(state.stack, expected_output_stack);
}
}
#[test]
fn test_resolve_with_parent() {
let test_cases = vec![
// (self, parent, expected)
(
vec![StackSym::Before(1), StackSym::Other(42)],
vec![StackSym::Before(0)],
vec![StackSym::Before(1), StackSym::Other(42)],
),
(
vec![StackSym::Before(2)],
vec![StackSym::Before(1)],
vec![StackSym::Before(3)],
),
(
vec![
StackSym::Before(2),
StackSym::Before(0),
StackSym::Other(99),
],
vec![
StackSym::Before(10),
StackSym::Before(9),
StackSym::Pushed([1, 2, 3, 4]),
],
vec![
StackSym::Before(10),
StackSym::Pushed([1, 2, 3, 4]),
StackSym::Other(99),
],
),
(
vec![
StackSym::Before(3),
StackSym::Before(1),
StackSym::Before(0),
],
vec![
StackSym::Before(5),
StackSym::Other(200),
StackSym::Other(201),
StackSym::Pushed([9, 9, 9, 9]),
StackSym::Other(202),
],
vec![
StackSym::Before(5),
StackSym::Other(200),
StackSym::Pushed([9, 9, 9, 9]),
StackSym::Other(202),
],
),
];
for (self_stack, parent_stack, expected_stack) in test_cases.into_iter() {
let self_state = State { stack: self_stack };
let parent_state = State {
stack: parent_stack,
};
let resolved_state = self_state.resolve_with_parent(&parent_state);
assert_eq!(resolved_state.stack, expected_stack);
}
}
}