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fix(avm): alu gadget fuzzer serialisation #19115

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Merged
IlyasRidhuan merged 1 commit into from
Feb 17, 2026
Merged

fix(avm): alu gadget fuzzer serialisation #19115

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24 changes: 12 additions & 12 deletions barretenberg/cpp/src/barretenberg/avm_fuzzer/harness/alu.fuzzer.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -44,8 +44,9 @@ struct AluFuzzerInput {
MemoryValue a;
MemoryValue b;
MemoryValue c = MemoryValue::from_tag(MemoryTag::FF, 0); // Placeholder for result
int op_id = 0; // For execution trace alu_op_id

uint16_t op_id = 0; // For execution trace alu_op_id
// We serialise MemoryValues as FF + 1 byte for tag to save 31 bytes per value:
static const size_t size = (3 * (sizeof(FF) + 1)) + sizeof(uint16_t);
// Serialize to buffer
void to_buffer(uint8_t* buffer) const
{
Expand All @@ -60,7 +61,7 @@ struct AluFuzzerInput {
buffer += sizeof(FF) + 1;
write_mem_value(buffer, c);
buffer += sizeof(FF) + 1;
serialize::write(buffer, static_cast<uint16_t>(op_id));
serialize::write(buffer, op_id);
}

static AluFuzzerInput from_buffer(const uint8_t* buffer)
Expand Down Expand Up @@ -90,11 +91,11 @@ struct AluFuzzerInput {

extern "C" size_t LLVMFuzzerCustomMutator(uint8_t* data, size_t size, size_t max_size, unsigned int seed)
{
if (size < sizeof(AluFuzzerInput)) {
if (size < AluFuzzerInput::size) {
// Initialize with default input
AluFuzzerInput input;
input.to_buffer(data);
return sizeof(AluFuzzerInput);
return AluFuzzerInput::size;
}

std::mt19937_64 rng(seed);
Expand All @@ -121,7 +122,6 @@ extern "C" size_t LLVMFuzzerCustomMutator(uint8_t* data, size_t size, size_t max

auto random_mem_value_from_tag = [&rng](MemoryTag tag) -> MemoryValue {
std::uniform_int_distribution<uint64_t> dist(0, std::numeric_limits<uint64_t>::max());
// TODO(MW): Use array?
FF value = FF(dist(rng), dist(rng), dist(rng), dist(rng));
// Do we want the option of making "invalid tag" values, where the value is out of range for the tag?
// These aren't currently possible with this function since MemoryValue::from_tag will throw in that case.
Expand All @@ -137,9 +137,9 @@ extern "C" size_t LLVMFuzzerCustomMutator(uint8_t* data, size_t size, size_t max
// Deserialize current input
AluFuzzerInput input = AluFuzzerInput::from_buffer(data);

// Choose random ALU operation
// Choose random ALU operation (11 possible operations with op_id = 2^index)
std::uniform_int_distribution<int> dist(0, 11);
input.op_id = 1 << dist(rng);
input.op_id = static_cast<uint16_t>(1 << dist(rng));

// Choose test case (TODO(MW): what else do we want here?)
dist = std::uniform_int_distribution<int>(0, 4);
Expand Down Expand Up @@ -189,18 +189,18 @@ extern "C" size_t LLVMFuzzerCustomMutator(uint8_t* data, size_t size, size_t max
// Serialize mutated input back to buffer
input.to_buffer(data);

if (max_size > sizeof(AluFuzzerInput)) {
return sizeof(AluFuzzerInput);
if (max_size > AluFuzzerInput::size) {
return AluFuzzerInput::size;
}

return sizeof(AluFuzzerInput);
return AluFuzzerInput::size;
}

extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size)
{
using bb::avm2::MemoryValue;

if (size < sizeof(AluFuzzerInput)) {
if (size < AluFuzzerInput::size) {
info("Input size too small");
return 0;
}
Expand Down
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