CPU Status Registers (EFLAGS/64-Bit RFLAGS)

Figure 3-6: EFLAGS register

Each 80x86 processor has standard status flags stored in an EFLAGS/ RFLAGS register, which indicate various conditions of the processor. In 64-bit mode the EFLAGS register is referred to as the 64-bit register RFLAGS, with the upper bits set to zero. As this book is written mainly for the application programmer there are only a few EFLAGS that you need to know initially. All the EFLAGS are defined in Chapter 18 but for now:

In this book you will find the following table with each general-purpose instruction description indicating the flags that it sets. Those flags are in reality the individual bits found in the EFLAGS register.

LAHF Load AH Flags

Mnemonic

P

PII

K6

3D!

3Mx+

SSE

SSE2

A64

SSE3

E64T

LAHF