x (SDM)

Allows you to examine and optionally modify the contents of NPX and CPU registers such as the thread state segment.

x [n] 
x [[cpu-reg][.bitname][=expression]] 
x [[npx-reg][=hex#|real#]] 
x tss [(expression)][.reg[=expression]]

For an example, click here.

Parameters

If you use the x command with no parameters, SDM displays the current contents of the CPU registers with respect to your application at the time the fault, trap, or break occurred.

n

Instructs SDM to display the contents of the NPX registers and NPX stack registers.

cpu-reg

The abbreviation for the Intel386, Intel486, or Pentium† microprocessor register that you want to display or modify.

If you do not include any other parameters, SDM displays the contents of the register or bit followed by a dash (-) prompt. At this point, to change the register or bit value, enter the new value followed by a <CR>. If you do not want to change the value, enter a <CR>.

The register abbreviations you can enter are listed below. Not all registers may be accessible on your CPU. For example, CR4 is not defined on the Intel386 microprocessor. Abbreviations include:

Register type	32-bit	16-bit	8-bit
General Registers	EAX EBX ECX EDX EBP ESI EDI	AX BX CX DX BP SI DI	AH BH CH DH	AL BL CL DL
Stack Pointer	ESP	SP
Code Segment	CS
Data Segment	DS
Stack Segment	SS
Extra Data Segments	ES FS GS
Flag Register	EFL	FL
Instruction Pointer	EIP	IP
Control Registers	CR0 CR1 CR2 CR3 CR4	MSW

The FL, EFL, MSW, CR0, CR3, and CR4 registers are special registers containing bit fields. SDM displays the contents of these registers first with the binary values and a mnemonic for each bit field, then as a hexadecimal word value. For example, the display of EFL might be as follows, where 0 or 1 as a mnemonic indicates a reserved bit field:

ID VIP VIF AC VM RF  0 NT IOPL OF DF IF TF SF ZF  0 AF  0 PF  1 CF
 0  0   0   0  0  0  0  0  00   0  0  1  0  0  1  0  0  0  1  1  0
00000246 -

The mnemonics for bit fields in the special registers are listed below.

EFL & FL	Bit Names	CR0 & MSW	Bit Names
AC	Alignment Check	AM	Alignment Mask
AF*	Auxiliary Carry Flag	CD	Cache Disable
CF*	Carry Flag	EM**	Emulation Mode (Coprocessor)
DF*	Direction Flag	ET**	Extension Type
IF*	Interrupt Enable Flag	MP**	Math Present (Monitor Coprocessor)
ID	Identification Flag	NE	Numerics Exception
IOPL*	I/O Privilege Level (2 bits)	NW	Not Write-Through
NT*	Nested Thread Flag	PE**	Protection Enable
OF*	Overflow Flag	PG	Paging Enable
PF*	Parity Flag	TS**	Thread Switch
RF	Resume Flag	WP	Write Protect
SF*	Sign Flag	CR3	Bit Names
TF*	Trap Enable Flag	PCD	Page Cache Disable
VIF	Virtual Interrupt Flag	PWT	Page Write-Through
VIP	Virtual Interrupt Pending	(no mnemonic)	Physical base addres of page director table in bits 12-31
VM	Virtual 8086 Mode	CR4	Bit Names
ZF*	Zero Flag	DE	Debugging Extensions
		MCE	Machine Check Enable
		PSE	Page Size Extensions
		PVI	Protected mode Virtual Interrupt
		TSD	Time Stamp Disable
		VME	Virtual 8086 Mode Extensions

* Bit fields in the Flags register (FL), which is a subset of EFL
** Bit fields in the Machine Status Word (MSW), which is a subset of CR0

.bitname

To display and change a single bit field from one of the special registers, follow the cpu-reg name with a period (.) and the mnemonic for the bit field. For example, to display only the Carry Flag from the Extended Flags register, you would enter:

x efl.cr

=expression

An expression that corresponds to a value you want to place in the register or TSS you specified. The equal sign (=) preceding the expression parameter instructs SDM to place the value in the register.

npx-reg

The abbreviation for the math coprocessor (NPX) register you want to display and optionally modify. The following lists the NPX registers and the abbreviations known to SDM.

Register Name	Abbreviation	Register Name	Abbreviation
NPX State	N	Status Word	SW
Control Word	CW	Tag Word	TW
Instrution Pointer	IP*	Data Pointer	DP*
Stack Register 0	ST(0)	Stack Register 4	ST(4)
Stack Register 1	ST(1)	Stack Register 5	ST(5)
Stack Register 2	ST(2)	Stack Register 6	ST(6)
Stack Register 3	ST(3)	Stack Register 7	ST(7)

* These registers cannot be modified.

If you do not include any further parameters, SDM displays the contents of the NPX register followed by a dash (-) prompt.

At this point, to change the register value, you can enter a value. Enter stack register values as real numbers; enter all other NPX registers values as words. You cannot modify the IP and DP registers for the NPX. If you do not want to change the NPX register value or display any further NPX register contents, enter a <CR>.

hex#

The hexadecimal number you want to place in the NPX register you specified.

real#

The real number you want to place in the NPX stack register you specified.

tss

The thread state segment (TSS) option instructs SDM to display the contents of the thread state segment. The contents of the TSS are listed in the next table.

To access TSS registers, use this parameter. If you do not include any further parameters, SDM displays the current contents of the TSS whose selector is in the TR register.

Name	Abbreviation
Local Descriptor Table Register	LDTR
Interrupt Descriptor Table Register	IDTR
Global Descriptor Table Register	GDTR
Thread Register	TR
Link to Nested Thread	LINK
Level 0 Stack Segment	SS0
Level 1 Stack Segment	SS1
Level 2 Stack Segment	SS2
Level 0 Stack Pointer	ESP0
Level 1 Stack Pointer	ESP1
Level 2 Stack Pointer	ESP2

(expression)

A selector for a TSS.

If you do not include any further parameters, SDM displays the contents of the indicated TSS.

.reg

The name of the TSS component that you wish to display. Include a period (.) before the component name so SDM can recognize the name.

If you do not include any further parameters, SDM displays the contents of the register in the TSS followed by a dash (-) prompt.

At this point, to change the TSS component register value, enter the new value followed by a <CR>. If you do not want to change the TSS contents, enter a <CR>.

Remarks

If you use the x command with both a register name and an expression, the modification you specify takes place immediately and SDM does not display the new value. If you redisplay the NPX state (after modification), SDM displays the results of the change you made.

You can use the x command to set the registers or the TSS contents to any value. If you use any invalid values, SDM reports them and does not execute the change.

Examples

This example shows the results of invoking the x command with no parameters on an Intel386-based board:

..x

SDM responds with this display:

EAX=0000FFFF  CS=1000  EIP=00000000  EFL=00000000  LDTR=2A0
EBX=0000FFFF  SS=0000  ESP=00000428  BP=0000FFFF   TR=278
ECX=0000FFFF  DS=0000  ESI=0000FFFF  FS=0000       MSW=FFF0
EDX=0000FFFF  ES=0000  EDI=0000FFFF  GS=0000
GDTR .BASE=00000000          .LIMIT=0000
IDTR .BASE=00000000          .LIMIT=0000

This example illustrates the results of invoking the x command with only the n option as a parameter:

..xn

SDM responds:

CW: X  X  X IC  R  C  P  C IM  X PM UM OM ZM DM IM 
    0  0  0  0  0  0  1  1  1  1  1  1  1  1  1  1   IP = 00000:0000
SW: B C3  T  O  P C2 C1 C0 IR  X PE UE OE ZE DE IE 
    0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0      
TW: T  7  T  6  T  5  T  4  T  3  T  2  T  1  T  0 
    0  0  0  0  1  1  1  0  1  0  0  0  0  0  0  1   DP = 00000:0000
ST(0) ZERO     00000000000000000000R   0
ST(1) VALID    3FFF999999999999999AR   1.2
ST(2) VALID    BFFF999999999999999AR  -1.2
ST(3) SPECIAL  FFFF0000000000000000R  -Infinity
ST(4) SPECIAL  7FFFFF00000000000000R  +NAN
ST(5) EMPTY    4000C90FDA9E46A7843ER   3.14159265
ST(6) VALID    4CF5F08B8D41AF800AC8R   1.23456E+999
ST(7) VALID    3FFF1800000000000000R   .1875 UNNORM 3 BITS

See also

CW, SW, and TW output fields, in the hardware reference manual for your microprocessor

This example instructs SDM to display the contents of the thread state segment whose selector is 068H:

..x tss(68)

SDM responds:

EAX=00001234 CS=0020 EIP=00000000 EFL=00000000 LDTR=02D0 LINK=0058
EBX=00001234 SS=0000 ESP=00000428 EBP=0000FFFF SS0=0020  ESP0=0000FFFE
ECX=00001234 DS=0000 ESI=0000FFFF  FS=0000     SS1=0000  ESP1=00000000
EDX=00001234 ES=0000 EDI=0000FFFF  GS=0000     SS2=0000  ESP2=00000000

Parameters

Remarks

Examples

See Also