# Debugger: Registers

Registers refer to the target processor's register banks. In multi-threaded environments, it is assumed that each thread has its own register context. The register window presents a subset of registers for the current thread understood by both the target and Ghidra's language model for the target processor. It permits for the selection, organization, display, search, modification, and analysis of the registers and values.

The register window uses colors to hint about the state of registers and their values. By default, changed registers are displayed in red, and stale registers are displayed in dark grey. A "stale" register is one whose current value is not known. The value displayed is the last recorded value or the default value 0. Simply, a "changed" register is one whose value has just changed. For example, if a register is modified as result of stepping, then that register is changed. However, given the possibility of rewinding, changing thread focus, etc., "changed" is actually subtly more flexible. The registers window remembers the user's last coordinates (time, thread, frame, etc.) as well as the current coordinates. So, "changed" more precisely refers to a register whose value differs between those two coordinates. This permits the user to switch focus between different coordinates and quickly identify what is different, so long as those coordinates pertain to the same processor language.

## Table Columns

The table displays information about registers, including their values and types. It has the following columns:

- Favorite - a toggle to mark the register as a favorite. By default this includes the program counter and stack pointer. Favorites are sorted to the top, by default. The list of favorite registers is memorized per compiler specification.
- Number - the index of the register in Ghidra's language model. By default, this is the second sort column.
- Name - the name of the register in Ghidra's language model.
- Value - the value of the register as recorded in the trace. When the value refers to a valid memory offset, right-clicking the row allows the user to navigate to that offset in a selected memory space. This field is user modifiable when the Enable Edits toggle is on, and the register is modifiable. Edits may be directed toward a live target, the trace, or the emulator. Values changed by the last event are displayed in red.
- Type - the type of the register as marked up in the trace. There is generally no default here. Either the user or some automation, e.g., analysis, may set this value. Changes to this field do not affect the target. The selected type is saved to the trace "from this time on."
- Representation - the value of the register as interpreted by its data type. If the value is an address, double-clicking this field will navigate to it. This field is user modifiable whenever the Value column is modifiable and the selected data type provides an encoder.

## Actions

The register window provides the following actions:

### Select Registers

This displays a dialog for selecting which registers to display in the table.

The dialog provides more information about each register, potentially displays a larger set of registers, and permits the precise selection of registers to include in the window. This varies from using the table filter in that the register window will not query the target for a register unless it is selected. Note that deselecting a register does not prohibit other components from reading that register. For example, the program counter and stack pointer are read by the recorder whether or not they're displayed in the table. The actions allow for the addition and subtraction of selections from the register set. Most columns are self-explanatory or duplicate the same column in the main window. The "Known" column indicates whether Ghidra was able to find the same register on the target. Unknown registers are never populated by the recorder, but they can still be populated by the user. Modifying the values of unknown registers cannot affect the target. Register sets are memorized per compiler specification.

### Register Type Settings

This action is available on the context menu when there is a single register selected with a data type assigned. It permits the adjustment of that data type's settings, e.g., to display decimal vs hexadecimal. The settings are saved to the data unit for the register.

### Enable Edits

This toggle is a write protector for machine state. To modify register values, this toggle must be enabled. Edits are directed according the to Control and Machine State Plugin. Note: Only the raw "Value" column can be edited directly. The "Repr" column cannot be edited, yet.

### Clone Window

This button is analogous to the "snapshot" action of other Ghidra windows. It generates a clone of this window. The clone will no longer follow the current thread, but it will follow the current time.