MpX

MPX, short for Memory Protection Extensions, is a hardware-assisted memory-safety feature introduced by Intel to provide bounds checking for pointers in C and C++ programs. The feature set includes new bound registers and instructions that allow the processor to enforce pointer bounds at runtime, helping detect out-of-bounds accesses, underflows, and overflows that can cause memory corruption.

Operation: At runtime, each pointer can have bound information stored in bound registers BND0–BND3 and a bounds table. Compilers instrument code to set and check these bounds for pointer operations. Before a memory load or store, the code checks that the address lies within the defined bounds; violations trigger a fault.

Hardware and software: MPX requires Intel processors with MPX support and operating-system support for bounds tables. Compiler support exists in GCC, Intel C++ Compiler, and Clang/LLVM in certain versions. Enabling MPX typically involves compiler flags and runtime libraries.

Adoption and limitations: MPX provides hardware-assisted memory safety but introduces runtime overhead and added memory usage. It has seen limited adoption due to performance costs and uneven ecosystem support; thus, it has not become a widely deployed safety mechanism.

See also memory safety, bounds checking, UBSan, ASan.