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[WIP] fix(fuzz): strip metadata when collecting push bytes #8139

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[WIP] fix(fuzz): strip metadata when collecting push bytes #8139

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20 changes: 17 additions & 3 deletions crates/evm/fuzz/src/strategies/state.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -10,7 +10,7 @@ use parking_lot::{lock_api::RwLockReadGuard, RawRwLock, RwLock};
use revm::{
db::{CacheDB, DatabaseRef, DbAccount},
interpreter::opcode,
primitives::AccountInfo,
primitives::{AccountInfo, Bytecode},
};
use std::{
collections::{BTreeMap, HashMap},
Expand Down Expand Up @@ -245,12 +245,26 @@ impl FuzzDictionary {
// Insert push bytes
if let Some(code) = &account_info.code {
self.insert_address(*address);
self.collect_push_bytes(code.bytes_slice());
self.collect_push_bytes(code);
}
}
}

fn collect_push_bytes(&mut self, code: &[u8]) {
fn collect_push_bytes(&mut self, code: &Bytecode) {
let mut code = code.original_byte_slice();
if code.is_empty() {
return;
}

// Remove metadata by looking up the last two bytes of original bytecode.
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is this always true?

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For initcode, no. Sometimes e.g. long strings in a constructor are after the metadata hash.

For runtime code, yes, IF the metadata hash is present. When bytecode_hash = none there is still a metadata hash containing the solidity version, so the last two bytes are still the length. When cbor_metadata = false then there is no bytecode hash at all and the last two bytes are code

To know for certain if what you have is a metadata hash, without knowing the compilation settings, you'd assume the last two bytes are the length of the metadata hash, then try CBOR decoding that hash. If it decodes successfully, it's a metadata hash, otherwise it's code.

Here is some old, probably bad, rust code I had that did this using ciborium: https://github.com/ScopeLift/cove-backend/blob/d8c875c5a64bf89a874892bc8ed57751c47b1233/src/bytecode.rs#L53-L97

if code.len() > 2 {
let metadata_len = &code[code.len() - 2..];
let metadata_len = u16::from_be_bytes([metadata_len[0], metadata_len[1]]).into();
if code.len() > metadata_len {
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this could still fail due to the -2, but not sure if possible

perhaps metadata_offset = metadata_len + 2

&code[..code.len() - metadata_offset];

code = &code[..code.len() - 2 - metadata_len];
}
}

let mut i = 0;
let len = code.len().min(PUSH_BYTE_ANALYSIS_LIMIT);
while i < len {
Expand Down
2 changes: 1 addition & 1 deletion crates/forge/tests/it/fuzz.rs
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Expand Up @@ -158,7 +158,7 @@ async fn test_persist_fuzz_failure() {
async fn test_scrape_bytecode() {
let filter = Filter::new(".*", ".*", ".*fuzz/FuzzScrapeBytecode.t.sol");
let mut runner = TEST_DATA_DEFAULT.runner();
runner.test_options.fuzz.runs = 2000;
runner.test_options.fuzz.dictionary.dictionary_weight = 100;
runner.test_options.fuzz.seed = Some(U256::from(6u32));
let suite_result = runner.test_collect(&filter);

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