State Management

Sogen provides comprehensive state management capabilities, allowing you to save complete emulator state to disk and restore it later, or create fast in-memory snapshots for rapid state restoration.

Overview

Sogen supports two types of state management:

Full Serialization: Complete emulator state saved to disk in a compressed format
In-Memory Snapshots: Fast snapshots for rapid state restoration (used by the fuzzer)

Both approaches capture the entire state of the Windows emulator including:

CPU registers and flags
Memory contents (all committed regions)
Loaded modules and their state
Thread contexts
File handles and I/O state
Registry state

Snapshot Files

Creating Snapshots

Create a snapshot of the current emulator state:

#include <snapshot.hpp>

windows_emulator win_emu{/* ... */};

// Run to desired state
win_emu.start();

// Create and save snapshot
auto snapshot_path = snapshot::write_emulator_snapshot(win_emu);
printf("Snapshot saved to: %s\n", snapshot_path.string().c_str());

Snapshot File Format

Snapshots use a custom binary format with compression:

// From src/analyzer/snapshot.cpp:10-17
struct snapshot_header
{
    char magic[4] = {'S', 'N', 'A', 'P'};  // File signature
    uint32_t version{1};                    // Format version
};

static_assert(sizeof(snapshot_header) == 8);

The file structure:

8-byte header (magic + version)
ZSTD-compressed emulator state

Creating Snapshots

The create_emulator_snapshot() function serializes and compresses state:

// From src/analyzer/snapshot.cpp:71-84
std::vector<std::byte> create_emulator_snapshot(const windows_emulator& win_emu)
{
    const auto state = get_compressed_emulator_state(win_emu);
    
    snapshot_header header{};
    std::span header_span(reinterpret_cast<const std::byte*>(&header), sizeof(header));
    
    std::vector<std::byte> snapshot{};
    snapshot.reserve(header_span.size() + state.size());
    snapshot.assign(header_span.begin(), header_span.end());
    snapshot.insert(snapshot.end(), state.begin(), state.end());
    
    return snapshot;
}

Writing to Disk

Snapshots are automatically named with timestamp:

// From src/analyzer/snapshot.cpp:86-102
std::filesystem::path write_emulator_snapshot(const windows_emulator& win_emu, const bool log)
{
    // Format: <executable>-<timestamp>.snap
    std::filesystem::path snapshot_file = 
        get_main_executable_name(win_emu) + "-" + 
        std::to_string(time(nullptr)) + ".snap";
    
    if (log) {
        win_emu.log.log("Writing snapshot to %s...\n", snapshot_file.string().c_str());
    }
    
    const auto snapshot = create_emulator_snapshot(win_emu);
    if (!utils::io::write_file(snapshot_file, snapshot)) {
        throw std::runtime_error("Failed to write snapshot!");
    }
    
    return snapshot_file;
}

Example filenames:

notepad-1701234567.snap
malware-1701234890.snap

Loading Snapshots

From File

Load a snapshot from disk:

#include <snapshot.hpp>

windows_emulator win_emu{create_x86_64_emulator()};

// Load snapshot
snapshot::load_emulator_snapshot(win_emu, "notepad-1701234567.snap");

// Continue execution from saved state
win_emu.start();

From Memory

Load from a buffer:

std::vector<std::byte> snapshot_data = /* ... */;
snapshot::load_emulator_snapshot(win_emu, snapshot_data);

Implementation

// From src/analyzer/snapshot.cpp:104-121
void load_emulator_snapshot(windows_emulator& win_emu, 
                           const std::span<const std::byte> snapshot)
{
    const auto data = get_decompressed_emulator_state(snapshot);
    
    utils::buffer_deserializer deserializer{data};
    win_emu.deserialize(deserializer);
}

void load_emulator_snapshot(windows_emulator& win_emu, 
                           const std::filesystem::path& snapshot_file)
{
    std::vector<std::byte> data{};
    if (!utils::io::read_file(snapshot_file, &data)) {
        throw std::runtime_error("Failed to read snapshot file: " + snapshot_file.string());
    }
    
    load_emulator_snapshot(win_emu, data);
}

Compression

ZSTD Compression

Snapshots use ZSTD compression for optimal size/speed ratio:

// From src/analyzer/snapshot.cpp:45-51
std::vector<std::byte> get_compressed_emulator_state(const windows_emulator& win_emu)
{
    utils::buffer_serializer serializer{};
    win_emu.serialize(serializer);
    
    return utils::compression::zstd::compress(serializer.get_buffer());
}

Decompression:

// From src/analyzer/snapshot.cpp:53-57
std::vector<std::byte> get_decompressed_emulator_state(const std::span<const std::byte> snapshot)
{
    const auto data = validate_header(snapshot);
    return utils::compression::zstd::decompress(data);
}

ZSTD provides:

Fast compression/decompression
High compression ratio (typically 70-90% size reduction)
Deterministic output

Validation

Header Validation

Snapshots are validated before loading:

// From src/analyzer/snapshot.cpp:19-43
std::span<const std::byte> validate_header(const std::span<const std::byte> snapshot)
{
    snapshot_header header{};
    constexpr snapshot_header default_header{};
    
    if (snapshot.size() < sizeof(header)) {
        throw std::runtime_error("Snapshot is too small");
    }
    
    memcpy(&header, snapshot.data(), sizeof(header));
    
    if (memcmp(default_header.magic, header.magic, sizeof(header.magic)) != 0) {
        throw std::runtime_error("Invalid snapshot");
    }
    
    if (default_header.version != header.version) {
        throw std::runtime_error(
            "Unsupported snapshot version: " + std::to_string(header.version) +
            "(needed: " + std::to_string(default_header.version) + ")");
    }
    
    return snapshot.subspan(sizeof(header));
}

This prevents:

Loading corrupt files
Loading incompatible snapshot versions
Loading non-snapshot files

Serialization Interface

Emulator Serialization

The windows_emulator class implements serialization:

// From src/windows-emulator/windows_emulator.hpp:166-167
void serialize(utils::buffer_serializer& buffer) const;
void deserialize(utils::buffer_deserializer& buffer);

These methods save/restore:

All CPU state (registers, flags)
Memory manager state
Module manager (loaded DLLs, exports, imports)
Process context (threads, handles)
File system state
Registry modifications
Network socket state

Application Settings

Application configuration is also serialized:

// From src/windows-emulator/windows_emulator.hpp:49-61
struct application_settings
{
    windows_path application{};
    windows_path working_directory{};
    std::vector<std::u16string> arguments{};
    
    void serialize(utils::buffer_serializer& buffer) const
    {
        buffer.write(this->application);
        buffer.write(this->working_directory);
        buffer.write_vector(this->arguments);
    }
    
    void deserialize(utils::buffer_deserializer& buffer)
    {
        buffer.read(this->application);
        buffer.read(this->working_directory);
        buffer.read_vector(this->arguments);
    }
};

In-Memory Snapshots

Fast Snapshot API

For performance-critical scenarios (like fuzzing), use in-memory snapshots:

// From src/windows-emulator/windows_emulator.hpp:169-170
void save_snapshot();
void restore_snapshot();

These provide:

Extremely fast save/restore (microseconds vs milliseconds)
No disk I/O
Perfect for repeated state restoration

Fuzzing Use Case

The fuzzer uses in-memory snapshots for performance:

// From src/fuzzer/main.cpp:88-103
fuzzer_executer(const std::span<const std::byte> data)
    : emulator_data(data)
{
    // Initial setup
    utils::buffer_deserializer deserializer{emulator_data};
    emu.deserialize(deserializer);
    
    // Create fast snapshot
    emu.save_snapshot();
    
    // Setup return hook
    const auto return_address = emu.emu().read_stack(0);
    emu.emu().hook_memory_execution(return_address, [&](const uint64_t) {
        emu.emu().stop();
    });
}

void restore_emulator()
{
    emu.restore_snapshot();  // Fast restore
}

For each fuzzing iteration:

Restore snapshot (microseconds)
Inject new input
Run emulation
Repeat

This is much faster than full deserialization for each iteration.

Use Cases

1. Malware Analysis

Save state before detonating malware:

windows_emulator win_emu{create_x86_64_emulator()};

// Setup clean environment
load_application(win_emu, "malware.exe");

// Save clean state
auto clean_state = snapshot::write_emulator_snapshot(win_emu);

// Run malware
win_emu.start();

// Restore to clean state
snapshot::load_emulator_snapshot(win_emu, clean_state);

// Run again with different conditions
win_emu.start();

2. Debugging

Save state at interesting points:

win_emu.callbacks.on_syscall = [&](uint32_t syscall_id, std::string_view name) {
    if (name == "NtCreateFile") {
        // Save state before file creation
        snapshot::write_emulator_snapshot(win_emu);
    }
    return instruction_hook_continuation::run;
};

3. Testing

Test different code paths from same starting point:

// Get to interesting function
run_to_target_function(win_emu);

// Save state
auto base_state = snapshot::create_emulator_snapshot(win_emu);

// Test path 1
win_emu.emu().reg(x86_register::rax, 0);
win_emu.start();
check_results();

// Restore and test path 2  
snapshot::load_emulator_snapshot(win_emu, base_state);
win_emu.emu().reg(x86_register::rax, 1);
win_emu.start();
check_results();

4. Fuzzing

The fuzzer uses snapshots for performance:

// Setup once
windows_emulator base_emu{create_x86_64_emulator()};
run_to_target(base_emu);

utils::buffer_serializer serializer{};
base_emu.serialize(serializer);
auto snapshot = serializer.move_buffer();

// For each fuzzer worker
windows_emulator worker_emu{create_x86_64_emulator()};
utils::buffer_deserializer deserializer{snapshot};
worker_emu.deserialize(deserializer);
worker_emu.save_snapshot();

// For each iteration
worker_emu.restore_snapshot();
inject_fuzzed_input(worker_emu);
worker_emu.start();

Performance Considerations

Snapshot Size

Snapshot size depends on:

Number of loaded modules
Amount of committed memory
Thread count
Open handles

Typical sizes:

Simple executable: 1-5 MB compressed
Complex application: 10-50 MB compressed
Game/large app: 100+ MB compressed

Compression Ratio

ZSTD typically achieves 70-90% compression:

100 MB uncompressed → 10-30 MB compressed
Memory contains many zeros (uncommitted pages are excluded)
Code sections compress very well

Save/Restore Time

Full serialization (disk):

Save: 10-100ms depending on size
Load: 10-100ms depending on size
Dominated by compression and I/O

In-memory snapshots:

Save: <1ms (memory copy)
Restore: <1ms (memory copy)
Perfect for tight loops

Best Practices

1. Snapshot Naming

Use descriptive names:

std::filesystem::path snapshot_file = 
    "malware-before-decryption-" + std::to_string(time(nullptr)) + ".snap";

2. Verify Snapshots

Check that snapshots load correctly:

try {
    snapshot::load_emulator_snapshot(win_emu, snapshot_file);
} catch (const std::exception& e) {
    printf("Failed to load snapshot: %s\n", e.what());
}

3. Clean Up Old Snapshots

Snapshots can consume significant disk space:

# Delete snapshots older than 7 days
find . -name "*.snap" -mtime +7 -delete

4. Use In-Memory for Hot Paths

If repeatedly restoring state:

// Save once
win_emu.save_snapshot();

// Restore many times (fast)
for (int i = 0; i < 1000000; i++) {
    win_emu.restore_snapshot();
    // ... test something ...
}

Troubleshooting

”Snapshot is too small”

File is corrupt or truncated. Ensure:

Full write completed before reading
File wasn’t modified externally

”Invalid snapshot”

File doesn’t have the correct magic bytes. Ensure:

File is actually a Sogen snapshot
File wasn’t corrupted

”Unsupported snapshot version”

Snapshot was created with a different version of Sogen. Snapshots are not backward/forward compatible across versions. Solution: Recreate snapshot with current Sogen version.

Large Snapshot Files

If snapshots are unexpectedly large:

Application may have allocated significant memory
Check for memory leaks in target application
Consider snapshotting earlier in execution

Source Code Reference

Key files:

src/analyzer/snapshot.hpp - Public snapshot API
src/analyzer/snapshot.cpp - Snapshot implementation
src/windows-emulator/windows_emulator.hpp - Serialization interface (lines 166-170)

Next Steps

Use snapshots with GDB Integration for debugging
Learn how Fuzzing leverages snapshots for performance
Explore Custom Backends for backend-specific considerations

Get Started

Core Concepts

Usage Guide

Advanced

​State Management

​Overview

​Snapshot Files

​Creating Snapshots

​Snapshot File Format

​Creating Snapshots

​Writing to Disk

​Loading Snapshots

​From File

​From Memory

​Implementation

​Compression

​ZSTD Compression

​Validation

​Header Validation

​Serialization Interface

​Emulator Serialization

​Application Settings

​In-Memory Snapshots

​Fast Snapshot API

​Fuzzing Use Case

​Use Cases

​1. Malware Analysis

​2. Debugging

​3. Testing

​4. Fuzzing

​Performance Considerations

​Snapshot Size

​Compression Ratio

​Save/Restore Time

​Best Practices

​1. Snapshot Naming

​2. Verify Snapshots

​3. Clean Up Old Snapshots

​4. Use In-Memory for Hot Paths

​Troubleshooting

​”Snapshot is too small”

​”Invalid snapshot”

​”Unsupported snapshot version”

​Large Snapshot Files

​Source Code Reference

​Next Steps

Build docs developers (and LLMs) love

State Management

Overview

Snapshot Files

Creating Snapshots

Snapshot File Format

Creating Snapshots

Writing to Disk

Loading Snapshots

From File

From Memory

Implementation

Compression

ZSTD Compression

Validation

Header Validation

Serialization Interface

Emulator Serialization

Application Settings

In-Memory Snapshots

Fast Snapshot API

Fuzzing Use Case

Use Cases

1. Malware Analysis

2. Debugging

3. Testing

4. Fuzzing

Performance Considerations

Snapshot Size

Compression Ratio

Save/Restore Time

Best Practices

1. Snapshot Naming

2. Verify Snapshots

3. Clean Up Old Snapshots

4. Use In-Memory for Hot Paths

Troubleshooting

”Snapshot is too small”

”Invalid snapshot”

”Unsupported snapshot version”

Large Snapshot Files

Source Code Reference

Next Steps