Make your own free website on Tripod.com

*

A

B

C

D

E

F

G

H

I

J

K

L

M

N

O

P

Q

R

S

T

U

V

W

X

Y

Z

?


Code Mnemonic Description
0F 00 /4 VERR r/m16 Set ZF=1 if segment specified with r/m16 can be read
0F 00 /5 VERW r/m16 Set ZF=1 if segment specified with r/m16 can be written

Description
Verifies whether the code or data segment specified with the source operand is readable (VERR) or writable (VERW) from the current privilege level (CPL). The source operand is a 16-bit register or a memory location that contains the segment selector for the segment to be verified. If the segment is accessible and readable (VERR) or writable (VERW), the ZF flag is set; otherwise, the ZF flag is cleared. Code segments are never verified as writable. This check cannot be performed on system segments.

To set the ZF flag, the following conditions must be met:

The validation performed is the same as is performed when a segment selector is loaded into the DS, ES, FS, or GS register, and the indicated access (read or write) is performed. The segment selector's value cannot result in a protection exception, enabling the software to anticipate possible segment access problems.

Operands Bytes Clocks
r16 3 7 NP
mem16 3 + d(0, 2) 7 NP

Flags
ID unaffected DF unaffected
VIP unaffected IF unaffected
VIF unaffected TF unaffected
AC unaffected SF unaffected
VM unaffected ZF sets to 1 if the segment is accessible and readable (VERR) or writable (VERW); otherwise, it is cleared to 0
RF unaffected AF unaffected
NT unaffected PF unaffected
IOPL unaffected CF unaffected
OF unaffected