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.
Possible errors:
ERROR_INVALID_ADDRESS (487)
ERROR_INVALID_SELECTOR (490)
ERROR_INVALID_PARAMETER (87)
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)