Set Descriptor Access Rights

Call With

AX = 0009H
BX = selector
CL = access rights/type byte
CH = 80386 extended access rights/type byte

Returns

if function successful
Carry flag = clear

if function unsuccessful
Carry flag = set
AX = error code

8021H	invalid value (access rights/type bytes invalid)
8022H	invalid selector
8025H	invalid linear address (changing the access rights/type bytes would cause the descriptor to reference a linear address range outside that allowed for DPMI clients.)

Notes

• The access rights/type byte passed to the function in CL has the following format:

  +---+---+---+---+---+---+---+---+
  | P |  DPL  | 1 |C/D|E/C|W/R| A |
  +-+-+---+---+-+-+-+-+-+-+-+-+-+-+
    |     |     |   |   |   |   |
    |     |     |   |   |   |   +- 0=not accessed, 1=accessed
    |     |     |   |   |   +----- data: 0=read, 1=>read/write
    |     |     |   |   |          code: must be 1 (readable)
    |     |     |   |   +--------- data: 0=expand-up, 1=expand-down
    |     |     |   |              code: must be 0 (non-conforming)
    |     |     |   +------------- 0=data, 1=code
    |     |     +----------------- must be 1
    |     +----------------------- must equal caller's CPL
    +----------------------------- 0=absent, 1=present
  

  If the Present bit is not set in the descriptor, the DPMI host allows any values except in the DPL and "must be 1" bit fields.

• On 80386 (and later) machines, the DPMI host interprets the value passed to the function in CH as follows:

  +---+---+---+---+---+---+---+---+
  | G |B/D| 0 |Avl|    Reserved   |
  +-+-+-+-+-+-+-+-+---+---+---+---+
    |   |   |   |         |
    |   |   |   |         +-- ignored
    |   |   |   +------------ can be 0 or 1
    |   |   +---------------- must be 0
    |   +-------------------- 0=default 16-bit, 1=default 32-bit
    +------------------------ 0=byte granular, 1=page granular
  

• A DPMI 1.0 host will reload any segment registers which contain the selector specified in register BX. It is suggested that DPMI 0.9 hosts also implement this.

• Client programs should use the LAR instruction to examine the access rights of a descriptor.

• Refer to the rules for descriptor usage in Appendix D.