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====== Int 31H, AH=00H, AL=09H ======

===== Version =====

0.9

===== Brief =====

Set Descriptor Access Rights

===== Input =====

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

===== Return =====

  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 =====

Modifies the access rights and type fields in the LDT descriptor for the specified segment.

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.

    
===== See also =====

   

===== Note =====

Text based on [[http://www.delorie.com/djgpp/doc/dpmi/]]

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