8. Descriptor Management Services, Continued

8.9 Set Descriptor Access Rights

This function allows a protected mode program to modify the access rights and type fields of a descriptor.

To Call

     AX = 0009h
     BX = Selector
     CL = Access rights/type byte
     CH = ia32 (32-bit) extended  access rights/type  byte
          (32-bit DPMI implementations only)

Returns

     If function was successful:
     Carry flag is clear.

     If function was not successful:
     Carry flag is set.

Programmer's Notes

• Since this function involves descriptor management, it will be rarely needed in 32-bit programs.
• This function will fail if the selector specified in BX is invalid.
• Your program should only modify descriptors that were allocated through the Allocate Descriptors function.
• To examine the access rights of a descriptor you should use the instruction lar (load access rights) which is supported on 80286 and ia32 (32-bit) machines.
• The access rights/type byte passed 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=>R/W
         |     |     |   |   |       Code: Must be 1 (readable)
         |     |     |   |   |
         |     |     |   |   +-- Data: 0=>Exp-up,
         |     |     |   |             1=>Exp-dn
         |     |     |   |       Code: Must be 0 (non-conform)
         |     |     |   |
         |     |     |   +-- 0=>Data, 1=>Code
         |     |     |
         |     |     +-- Must be 1
         |     |
         |     +-- Must equal caller's CPL
         |
         +- 0=>Absent, 1=>Present
  
  16-bit  DPMI   implementations  will   ignore  the
            extended access rights/type byte passed in CH even
            if it  is running on an ia32 (32-bit) system.  32-bit DPMI
            implementations  interpret  the  CH  parameter  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  parameter   which  does   not  meet  the  above
            requirements is  invalid, and  causes the function
            to return with the carry flag set.