DevHelp PhysToGDTSel

This service maps a given GDT selector to a specified physical address, setting the access byte of the descriptor to the desired privilege value. The specified segment size must be less than or equal to 64KB.

Syntax

C

USHORT APIENTRY DevHelp_PhysToGDTSel( ULONG PhysAddr,
                                      ULONG Count,
                                      SEL   Selector,
                                      UCHAR Access)

Assembler

MOV   EAX,PhysAddress     ; 32-bit physical address that the
                          ;    GDT selector is to be mapped to
MOV   ECX,Size            ; Size of segment mapped;
                          ;    must be less than or equal to 64KB
                          ;    (a 0 value will map a 64KB segment)
MOV   SI,Selector         ; GDT selector (allocated using AllocateGDTSelector)
MOV   DH,Access           ; Descriptor's type and privilege level
                          ; = 0  The selector is mapped as Ring 3, readable code
                          ;      with 16-bit addressing/operand
                          ;      size (286 format).
                          ; = 1 (binary 0001)  The selector is mapped as Ring 3,
                          ;     writable data.
                          ; = 3 (binary 0011)  The selector is mapped as Ring 2,
                          ;     IOPL, readable code with 16-bit
                          ;     addressing/operand size.
                          ; = 4 (binary 0100)  The selector is mapped as Ring 2,
                          ;     IOPL, writable data.
                          ; = 5 (binary 0101)  The selector is mapped as Ring 0,
                          ;     readable code with 16-bit addressing/operand size.
                          ; = 6 (binary 0110)  The selector is mapped as Ring 0,
                          ;     writable data.
                          ; = 128 (binary 10000000)  The selector will be mapped
                          ;     as Ring 3, readable code with 32-bit
                          ;     addressing/operand size.
                          ; = 131 (binary 10000011)  The selector will be mapped
                          ;       as Ring 2, IOPL, readable code with 32-bit
                          ;       addressing/operand size.
                          ; = 133 (binary 10000101)  The selector will be mapped
                          ;       as Ring 0, readable code with 32-bit
                          ;       addressing/operand size.
                          ; All other values are invalid.

MOV   DL,DevHlp_PhysToGDTSel

CALL  [Device_Help]

Parameters

C

PhysAddr (ULONG)

32-bit physical address that the GDT selector is to be mapped to.

Count (ULONG)

Count of bytes to be mapped, must be less than or equal to 64KB.

Selector (SEL)

GDT selector (allocated using AllocateGDTSelector)

Access (UCHAR)

Descriptor's type and privilege level:

GDTSEL_R3CODE - The selector is mapped as ring 3, readable code with 16-bit addressing/operand size (286 format).

GDTSEL_R3DATA - (binary 0001) The selector is mapped as ring 3 writable data.

GDTSEL_R2CODE - (binary 0011) The selector is mapped as ring 2, IOPL, readable code with 16-bit addressing/operand size.

GDTSEL_R2DATA - (binary 0100) The selector is mapped as ring 2, IOPL, writable data.

GDTSEL_R0CODE - (binary 0101) The selector is mapped as ring 0, readable code with 16-bit addressing/operand size.

GDTSEL_R0DATA - (binary 0110) The selector is mapped as ring 0, writable data.

GDTSEL_ADDR32 - (binary 10000000) The selector will be mapped as ring 3 readable code with 32-bit addressing/operand size.

GDTSEL_R2CODE/GDTSEL_ADDR32 - (binary 10000011) The selector will be mapped as ring 2, IOPL, readable code with 32-bit addressing/operand size.

GDTSEL_R0CODE/GDTSEL_ADDR32 - (binary 10000101) The selector will be mapped as ring 0 readable code with 32-bit addressing/operand size.

All other values are invalid.

Assembler

MOV   EAX,PhysAddress     ; 32-bit physical address that the
                          ;    GDT selector is to be mapped to
MOV   ECX,Size            ; Size of segment mapped;
                          ;    must be less than or equal to 64KB
                          ;    (a 0 value will map a 64KB segment)
MOV   SI,Selector         ; GDT selector (allocated using AllocateGDTSelector)
MOV   DH,Access           ; Descriptor's type and privilege level
                          ; = 0  The selector is mapped as Ring 3, readable code
                          ;      with 16-bit addressing/operand
                          ;      size (286 format).
                          ; = 1 (binary 0001)  The selector is mapped as Ring 3,
                          ;     writable data.
                          ; = 3 (binary 0011)  The selector is mapped as Ring 2,
                          ;     IOPL, readable code with 16-bit
                          ;     addressing/operand size.
                          ; = 4 (binary 0100)  The selector is mapped as Ring 2,
                          ;     IOPL, writable data.
                          ; = 5 (binary 0101)  The selector is mapped as Ring 0,
                          ;     readable code with 16-bit addressing/operand size.
                          ; = 6 (binary 0110)  The selector is mapped as Ring 0,
                          ;     writable data.
                          ; = 128 (binary 10000000)  The selector will be mapped
                          ;     as Ring 3, readable code with 32-bit
                          ;     addressing/operand size.
                          ; = 131 (binary 10000011)  The selector will be mapped
                          ;       as Ring 2, IOPL, readable code with 32-bit
                          ;       addressing/operand size.
                          ; = 133 (binary 10000101)  The selector will be mapped
                          ;       as Ring 0, readable code with 32-bit
                          ;       addressing/operand size.
                          ; All other values are invalid.

Return Code

C

Success Indicator: 0 if pages locked, returns selector with modified Request Privilege Level (RPL) bits.

Assembler

 'C' Clear if pages locked.
     SI = Selector with the modified RPL (Requested Privilege Level) bits.
 
 'C' Set if segment unavailable.
     EAX = Error code.

Possible errors

ERROR_INVALID_ADDRESS (487)

ERROR_INVALID_SELECTOR (490)

ERROR_INVALID_PARAMETER (87)

Remarks

The physical memory that is being mapped must be fixed or locked prior to the call to this service. After the call has been issued for a particular selector, the addressability remains valid until the physical device driver changes its content with a subsequent call to the DevHlp services PhysToGDTSel, PhysToGDTSelector, PageListToGDTSelector, or LinToGDTSelector.

Example Code

C

#include  "dhcalls.h"

USHORT APIENTRY DevHelp_PhysToGDTSel( ULONG PhysAddr,
                                      ULONG Count,
                                      SEL   Selector,
                                      UCHAR Access)