Gdb-vim

Simple cheat sheet for getting gdb working with vim in order to create a simple multi-screen development environment.

REQUIREMENTS

1. Upgrade vim > 8.1 https://itsfoss.com/vim-8-release-install/

2. Check Gdb > 8.1 is installed and working https://www.thegeekstuff.com/2010/03/debug-c-program-using-gdb/ upgrade Gdb trick https://stackoverflow.com/questions/32773255/how-to-update-gdb-to-most-current-stable-version

3. vim/gdb Usage intro https://www.dannyadam.com/blog/2019/05/debugging-in-vim/ https://vimhelp.org/terminal.txt.html

4. basic tutorial Gdb https://www.howtoforge.com/tutorial/how-to-debug-c-programs-in-linux-using-gdb/ https://www.thegeekstuff.com/2010/03/debug-c-program-using-gdb/

Gdb Docs:

TOC http://sourceware.org/gdb/current/onlinedocs/gdb/ Download pdf https://www.sourceware.org/gdb/documentation/

1. Basic setup and usage

Invoke Termdebug

:packadd termdebug

:Termdebug [name of file - without the .c]

Run a file with args

GDB win : r(un) [args]

Vim status:

:Run [args]

:Stop,

:Over execute the gdb "next" command (:Next is a Vim command)

:Continue

Close dbg

CTR+d

q(uit)

Window Management

Get into main vim window, then :

:set number <-- set up numbering for debugging

CTR-W then L <-- cap L shifts vim win to vertical Right

:vertical res 80 <--still in main vim window - 80 chars wide

Move between the gdb and vim editor windows

CTR-W w (cycle windows)

Or,

CTR-W p (previous window)

Move from vim directly into GDB window

:Gdb

:redraw! <-- get rid of artefacts after accidental gdb mouseover

GDB Window instructions

file [name of file - no .c]

r(un) [args]

p(rint) <-- var - dump a var

b(reak) <-- set break at line number

d(elete) <-- rm break

r[un] <-- Run to next breakpoint or to end

s[tep] <-- Single-step, descending into functions

n[ext] <-- Single-step without descending into functions

fin[ish] <-- Finish current function, loop, etc. (useful!)

c[ontinue] <-- Continue to next breakpoint or end

up <-- Go up one context level on stack (to caller)

do[wn] <-- Go down one level (only possible after up)

OR use Vim editor win

Click on Run / Step etc with mouse

:Next etc on cmd line

:Break to set break points

:Clear to delete break points

:Over execute the gdb "next" command (:Next is a Vim command)

Inspect a var

p(rint) var

Vim status bar :

:Eval var

:Eval + highlight (mouseover) var

:Eval (current line in editor)

or,

mouseover var and pres K

Workflow

load vim with file to edit

evoke gdb

sort out place of windows

set number <-- turn on vim line numbering

load file into gdb 'file [filename sans .c]'

OR when evoking gdb

compile with :

!gcc -g -Wall [filename.c] -o [filename sans .c]
-g dbg on -o output file -Wall enables all compiler's warning

r(un) [args]

2 GDB commands - more complex

Logging gdb output

set logging on [off] <-- default gdb.txt

set logging file [filename]

set logging overwrite [else appending]

create a dir and turn on logging for that file:

!mkdir dbg

set logging file dbg/myfile.txt

set logging on

Repeating commands

n(ext) 3 <--jump 3 lines, including this line

s(tep) 3

(blank line - return) <-- repeat last command

Default args (if repeatedly runnning the same test data)

set args [args] <--set a default arg to use for all following invocations

show args

Array size limiting

set print elements 10 <-- max limit the no of array element to be shown at any time

Rewind/restart:

(do some debug - get to a point to freeze)

checkpoint <-- returns this checkpoint-id eg 1

(go on and do some further dbg)

restart 1 <-- restart at previous checkpoint

delete checkpoint 1 <-- optionally clean up

NB A checkpoint is an identical copy of a process. Therefore if you create a checkpoint at (eg.) the start of main, and simply return to that checkpoint instead of restarting the process, you can avoid the effects of address randomization and your symbols will all stay in the same place.

frame : e.g. a function being called,

fin(ish) drop out of current frame and output to screen any return value of function