CPU Status Registers (EFLAGS64-Bit RFLAGS)

CPU Status Registers (EFLAGS/64-Bit RFLAGS)

image from book
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:

Table 3-9: RFLAG/EFLAG(s) and bit encoding

EFLAG

Code

Bit

Flag Descriptions

EFLAGS_CF

000000001h

Carry

EFLAGS_PF

000000004h

2

Parity

EFLAGS_AF

000000010h

4

Auxiliary Carry

EFLAGS_ZF

000000040h

6

Zero

EFLAGS_SF

000000080h

7

Sign

EFLAGS_OF

000000800h

11

Overflow

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.

Flags

O.flow

Sign

Zero

Aux

Parity

Carry

 

-

-

-

-

-

-

LAHF Load AH Flags

Mnemonic

P

PII

K6

3D!

3Mx+

SSE

SSE2

A64

SSE3

E64T

LAHF



32.64-Bit 80X86 Assembly Language Architecture
32/64-Bit 80x86 Assembly Language Architecture
ISBN: 1598220020
EAN: 2147483647
Year: 2003
Pages: 191

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