Editing Valgrind (section)

==Overview==
Valgrind is in essence a [[virtual machine]] using [[just-in-time compilation]] techniques, including [[dynamic recompilation]]. Nothing from the original program ever gets run directly on the host [[Central processing unit|processor]]. Instead, Valgrind first translates the program into a temporary, simpler form called [[intermediate representation]] (IR), which is a processor-neutral, [[static single assignment form]]-based form. After the conversion, a tool (see below) is free to do whatever transformations it would like on the IR, before Valgrind translates the IR back into machine code and lets the host processor run it. Valgrind recompiles [[binary code]] to run on host and target (or simulated) CPUs of the same architecture. It also includes a [[GDB]] stub to allow debugging of the target program as it runs in Valgrind, with "monitor commands" that allow querying the Valgrind tool for various information.

A considerable amount of performance is lost in these transformations (and usually, the code the tool inserts); usually, code run with Valgrind and the "none" tool (which does nothing to the IR) runs at 20% to 25% of the speed of the normal program.<ref>[https://valgrind.org/info/about.html Valgrind homepage]</ref><ref>[https://valgrind.org/docs/manual/valgrind_manual.pdf Valgrind Manual]</ref>