# Linux Kernel Module Cheat

##### 29.8.3.1. x86 REP prefix

Example: userland/arch/x86_64/rep.S

Repeat a string instruction RCX times:

As the repetitions happen:

- RCX decreases, until it reaches 0

- RDI and RSI increase

The variants: REPZ, REPNZ (alias REPE, REPNE) repeat a given instruction until something happens.

REP and REPZ also additionally stop if the comparison operation they repeat fails.

- REP: INS, OUTS, MOVS, LODS, and STOS

- REPZ: CMPS and SCAS