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GDB Text User Interface

The GDB Text User Interface, TUI in short, is a terminal interface which uses the curses library to show the source file, the assembly output, the program registers and GDB commands in separate text windows.

The TUI is enabled by invoking GDB using either `gdbtui' or `gdb -tui'.

TUI overview

The TUI has two display modes that can be switched while GDB runs:

In the TUI mode, GDB can display several text window on the terminal:

command
This window is the GDB command window with the GDB prompt and the GDB outputs. The GDB input is still managed using readline but through the TUI. The command window is always visible.
source
The source window shows the source file of the program. The current line as well as active breakpoints are displayed in this window.
assembly
The assembly window shows the disassembly output of the program.
register
This window shows the processor registers. It detects when a register is changed and when this is the case, registers that have changed are highlighted.

The source and assembly windows show the current program position by highlighting the current line and marking them with the `>' marker. Breakpoints are also indicated with two markers. A first one indicates the breakpoint type:

B
Breakpoint which was hit at least once.
b
Breakpoint which was never hit.
H
Hardware breakpoint which was hit at least once.
h
Hardware breakpoint which was never hit.

The second marker indicates whether the breakpoint is enabled or not:

+
Breakpoint is enabled.
-
Breakpoint is disabled.

The source, assembly and register windows are attached to the thread and the frame position. They are updated when the current thread changes, when the frame changes or when the program counter changes. These three windows are arranged by the TUI according to several layouts. The layout defines which of these three windows are visible. The following layouts are available:

On top of the command window a status line gives various information concerning the current process begin debugged. The status line is updated when the information it shows changes. The following fields are displayed:

target
Indicates the current gdb target (see section Specifying a Debugging Target).
process
Gives information about the current process or thread number. When no process is being debugged, this field is set to No process.
function
Gives the current function name for the selected frame. The name is demangled if demangling is turned on (see section Print settings). When there is no symbol corresponding to the current program counter the string ?? is displayed.
line
Indicates the current line number for the selected frame. When the current line number is not known the string ?? is displayed.
pc
Indicates the current program counter address.

TUI Key Bindings

The TUI installs several key bindings in the readline keymaps (see section Command Line Editing). They allow to leave or enter in the TUI mode or they operate directly on the TUI layout and windows. The TUI also provides a SingleKey keymap which binds several keys directly to GDB commands. The following key bindings are installed for both TUI mode and the GDB standard mode.

C-x C-a
C-x a
C-x A
Enter or leave the TUI mode. When the TUI mode is left, the curses window management is left and GDB operates using its standard mode writing on the terminal directly. When the TUI mode is entered, the control is given back to the curses windows. The screen is then refreshed.
C-x 1
Use a TUI layout with only one window. The layout will either be `source' or `assembly'. When the TUI mode is not active, it will switch to the TUI mode. Think of this key binding as the Emacs C-x 1 binding.
C-x 2
Use a TUI layout with at least two windows. When the current layout shows already two windows, a next layout with two windows is used. When a new layout is chosen, one window will always be common to the previous layout and the new one. Think of it as the Emacs C-x 2 binding.
C-x o
Change the active window. The TUI associates several key bindings (like scrolling and arrow keys) to the active window. This command gives the focus to the next TUI window. Think of it as the Emacs C-x o binding.
C-x s
Use the TUI SingleKey keymap that binds single key to gdb commands (see section TUI Single Key Mode).

The following key bindings are handled only by the TUI mode:

PgUp
Scroll the active window one page up.
PgDn
Scroll the active window one page down.
Up
Scroll the active window one line up.
Down
Scroll the active window one line down.
Left
Scroll the active window one column left.
Right
Scroll the active window one column right.
C-L
Refresh the screen.

In the TUI mode, the arrow keys are used by the active window for scrolling. This means they are available for readline when the active window is the command window. When the command window does not have the focus, it is necessary to use other readline key bindings such as C-p, C-n, C-b and C-f.

TUI Single Key Mode

The TUI provides a SingleKey mode in which it installs a particular key binding in the readline keymaps to connect single keys to some gdb commands.

c
continue
d
down
f
finish
n
next
q
exit the SingleKey mode.
r
run
s
step
u
up
v
info locals
w
where

Other keys temporarily switch to the GDB command prompt. The key that was pressed is inserted in the editing buffer so that it is possible to type most GDB commands without interaction with the TUI SingleKey mode. Once the command is entered the TUI SingleKey mode is restored. The only way to permanently leave this mode is by hitting q or `C-x s'.

TUI specific commands

The TUI has specific commands to control the text windows. These commands are always available, that is they do not depend on the current terminal mode in which GDB runs. When GDB is in the standard mode, using these commands will automatically switch in the TUI mode.

info win
List and give the size of all displayed windows.
layout next
Display the next layout.
layout prev
Display the previous layout.
layout src
Display the source window only.
layout asm
Display the assembly window only.
layout split
Display the source and assembly window.
layout regs
Display the register window together with the source or assembly window.
focus next | prev | src | asm | regs | split
Set the focus to the named window. This command allows to change the active window so that scrolling keys can be affected to another window.
refresh
Refresh the screen. This is similar to using C-L key.
tui reg float
Show the floating point registers in the register window.
tui reg general
Show the general registers in the register window.
tui reg next
Show the next register group. The list of register groups as well as their order is target specific. The predefined register groups are the following: general, float, system, vector, all, save, restore.
tui reg system
Show the system registers in the register window.
update
Update the source window and the current execution point.
winheight name +count
winheight name -count
Change the height of the window name by count lines. Positive counts increase the height, while negative counts decrease it.
tabset
Set the width of tab stops to be nchars characters.

TUI configuration variables

The TUI has several configuration variables that control the appearance of windows on the terminal.

set tui border-kind kind
Select the border appearance for the source, assembly and register windows. The possible values are the following:
space
Use a space character to draw the border.
ascii
Use ascii characters + - and | to draw the border.
acs
Use the Alternate Character Set to draw the border. The border is drawn using character line graphics if the terminal supports them.
set tui active-border-mode mode
Select the attributes to display the border of the active window. The possible values are normal, standout, reverse, half, half-standout, bold and bold-standout.
set tui border-mode mode
Select the attributes to display the border of other windows. The mode can be one of the following:
normal
Use normal attributes to display the border.
standout
Use standout mode.
reverse
Use reverse video mode.
half
Use half bright mode.
half-standout
Use half bright and standout mode.
bold
Use extra bright or bold mode.
bold-standout
Use extra bright or bold and standout mode.


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