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description
Description of the 'r' command in HyperDbg.

r (read or modify registers)

Command

r

Syntax

r

r [Register (string)] [= Expr (string)]

Description

Reads or modifies registers when the debuggee is paused.

Parameters

[Register (string)] (optional)

The register that needs to be read or modified.

[= Expr (string)] (optional)

The value or the expression that needs to be evaluated and modify the target register.

{% hint style="info" %} If you don't specify any parameters to the 'r' command, it shows all general-purpose + segment registers. {% endhint %}

{% hint style="success" %} The first parameter to this command is a register (not an expression). If you want to evaluate and see the result of registers as an expression (e.g., rax+rbx+rcx) then you can use the '.formats' command. {% endhint %}

Examples

If you want to see all general purpose and segment registers.

0: kHyperDbg> r
RAX=ffff948cc1ba4780 RBX=ffff948cc02f19e0 RCX=0000000000000024
RDX=0000000000000000 RSI=0000000000000000 RDI=ffff948cc23403a0
RIP=fffff80168d91262 RSP=ffff9305483f3698 RBP=0000000000000002
R8=0000000000000000  R9=0000000000000000  R10=0000000048564653
R11=0000564d43414c4c R12=4e4f485950455256 R13=0000000000000000
R14=ffff948cc23403a0 R15=ffff948cc05556b0 IOPL=00
OF 0  DF 0  IF 1  SF  0
ZF 1  PF 1  CF 0  AXF 0
CS=0010 SS=0018 DS=002b ES=002b FS=0053 GS=002b
RFLAGS=0000000000040246

If you want to see one special register (e.g., rax).

0: kHyperDbg> r rax
rax=ffff948cc1ba4780

If you want to see one special register (e.g., cs).

0: kHyperDbg> r cs
cs=0000000000000010

If you want to change a register to a constant hex value.

0: kHyperDbg> r rax = 10

If you want to change a register to a new value which is the result of an expression.

0: kHyperDbg> r rcx = rax + rdx + 10

IOCTL

This commands works over serial by sending the serial packets to the remote computer.

First of all, you should fill the following structure, set the RegisterId to your special register number, which is an ID from REGS_ENUM enum.

If you want to view all the registers, then you should set RegisterID to DEBUGGEE_SHOW_ALL_REGISTERS .

typedef struct _DEBUGGEE_REGISTER_READ_DESCRIPTION {

  UINT32 RegisterID; // the number is from REGS_ENUM
  UINT64 Value;
  UINT32 KernelStatus;

} DEBUGGEE_REGISTER_READ_DESCRIPTION, *PDEBUGGEE_REGISTER_READ_DESCRIPTION;

The next step is sending the above structure to the debuggee when debuggee is paused and waiting for new command on vmx-root mode.

You should send the above structure with DEBUGGER_REMOTE_PACKET_REQUESTED_ACTION_ON_VMX_ROOT_READ_REGISTERS as RequestedAction and DEBUGGER_REMOTE_PACKET_TYPE_DEBUGGER_TO_DEBUGGEE_EXECUTE_ON_VMX_ROOT as PacketType.

In return, the debuggee sends the above structure with the following type.

DEBUGGER_REMOTE_PACKET_REQUESTED_ACTION_DEBUGGEE_RESULT_OF_READING_REGISTERS

In the returned structure, the KernelStatus is filled by the kernel.

If the KernelStatus is DEBUGEER_OPERATION_WAS_SUCCESSFULL, then the operation was successful. Otherwise, the returned result is an error.

The following function is responsible for sending read register buffers in the debugger.

BOOLEAN KdSendReadRegisterPacketToDebuggee(PDEBUGGEE_REGISTER_READ_DESCRIPTION RegDes);

If you specified DEBUGGEE_SHOW_ALL_REGISTERS then the debuggee sends the registers with two buffers that are appended. The first buffer is GUEST_REGS and the second buffer is GUEST_EXTRA_REGISTERS.

The first buffer contains general-purpose registers, and the second buffer contains other registers, including segment registers.

Note that modifying registers are performed through script-engine as we might need the evaluation of expressions to get the register's value.

Remarks

This command is guaranteed to keep debuggee in a halt state (in Debugger Mode); thus, nothing will change during its execution.

Requirements

None

Related

None