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Record, Rewind & Replay Technology for Debugging

Replay the behaviour of Linux and Android software down to single instruction granularity

The Undo Engine, the underlying technology that makes Undo’s innovative products, records non-deterministic data and recomputes deterministic data on-the-fly. Recreate your application’s entire memory and register state on demand at any point in its execution with minimal overhead.

  • It's not fancy logging

    Simply logging everything that the program does would produce an unmanageable amount of data
  • No kernel changes

    We don’t require a particular kernel or any kernel modules to be loaded. The Undo Engine is compatible with most mainstream Linux distributions
  • No special hardware

    Our approach is not limited to systems with hardware tracing modules or performance counters
  • Debug ordinary native code

    Threads, signals, and shared memory and device interactions are all supported and recorded as non-deterministic events
  • Compiler- and library-agnostic

    We don’t require the application to be recompiled or linked against particular libraries (except if your application uses Asynchronous I/O)
  • Faster than you think

    Without specialized technology, recording large applications would be unusuably slow. Undo aims for a slowdown factor better than 5x in most applications.

Award–winning technology

Cambridge Top Innovation 2016

Cambridge News

2016 FinTech Innovation Lab winner

FinTech Innovation Lab

Live Recorder: Best Software Product

ARM TechCon 2015 Innovation Challenge

Discovering Start-Ups 2015 winner

Cambridge Wireless

Cool Vendor in Application Development

Gartner Cool Vendor

Foundations that make this work

The panels below show some of the core foundations that enable our record, rewind and replay approach in a wide variety of use cases.

Technology foundations, instrumentation


The Undo Engine performs a JIT (just-in-time) binary translation of your application’s machine code as it executes, which allows it to capture all sources of non-determinism such as system calls, signals, thread switches and reads from shared memory or device maps.

Technology foundations, snapshots


As your program runs, the Undo Engine stores snapshots of the program address space. These are complete copies of the current state of the program, but since they’re created using the Linux copy-on-write mechanism the impact on your system memory usage is kept to a minimum.

Technology foundations, event log

Event log

Results of each non-deterministic operation are recorded in an event log stored in the memory of your application process. These non-deterministic operations usually represent a tiny fraction of the instructions executed so the event log is smaller than you might expect. Configure it as a circular buffer, capturing only the most recent history leading up to the bug.

Technology foundations, searching


It’s possible to replay an application from any point in time by restoring the program state from a snapshot that was taken prior to that point and running it forwards, re-executing only the deterministic operations. The results of non-deterministic operations are synthesised based on what is stored in the event log.

Our technology in context

Several tools can help you find bugs in your programs. See how we’re different.

Features Other providers Undo
Core dumps Receive a snapshot of the state of the program at the moment that it crashed. View the entire history of the program’s execution and state. Wind back from the moment that it crashed to see the root cause.
Static analysis/profiling tools Receive reports of potential issues in your code, including theoretical and false positives.

Record actual failures and solve problems that you are experiencing right now.

Logging Receive a coarse history of your program’s execution without a full explanation as to why the program took the course that it did.

View the entire program’s execution and state (not just what you chose to log). Examine the contents of any variable or memory and see how they change over time.

Assertions It’s good programming technique to use assertions liberally in your code but when one fails, it is difficult to locate the root cause.

Run your code until the assertion fails and then work backwards (and forwards) to zero in on the root cause.

General purpose debuggers Gingerly step forwards in an attempt to reach (but not go past) the location of the error and re-run multiple times.

Run your program once, attack the problem from two directions, and backtrack easily to see exactly what happened and why.

Other record and replay technologies Limited support for shared memory or specific CPUs/kernels/VMs. Often unable to attach to a running process or defer recording. Our technology supports all of these features, and has a team dedicated to product development to help meet your needs.