GWPSan depends on specific features of compiler, and kernel, with the runtime implementing a binary analysis framework based on decoding and emulating instructions. In the below we describe the runtime components.
Machine code is decoded into abstract ISA instructions (Instr class in
instruction.h) by InstrDecoder::Decode method using
DynamoRIO framework. Abstract instructions are
executed/emulated by CPUContext::Execute. CPUContext class holds machine
context (registers) along with meta information (taint bits/origins). Env
class abstracts machine memory (e.g. can do actual stores to memory, or discard
stores) and stores meta information for values in memory.
The unified tool receives periodic timer signals, and speculatively executes some amount of instructions for the thread. As it executes instructions it looks for potential instructions of interest (memory accesses for data races detection, etc). If it finds any, it dispatches to the concrete tools to do the checking.