Debugging Modern C++ Application with Gdb

2. GDB (GNU DEBUGGER)
senkumar@juniper.net
Debugging Modern C++ Application with
For a fish, the archer fish is known to shoot down bugs from low hanging plants by spitting water at them.
Debugging is twice as hard as writing the code in the first place.
Therefore, if you write the code as cleverly as possible, you are, by
definition, not smart enough to debug it.
- Brian Kernighan

3. DISCLAIMER
The opinions expressed in this presentation and on the following
slides are solely those of the presenter. Neither the presenter
guarantee the accuracy or reliability of the information provided
herein.
May you do good and not evil. May you find forgiveness for yourself and forgive others. May you share freely, never taking more than you give!

4. SIMPLEST
DEBUG TOOL?

5. printf cout

6. NEXT SIMPLEST
DEBUG TOOL?

7. assert

8. WHAT IS?
Bug, Debug, Debugging, …
Coder: code
will produce
output X …
Computer:
code will
produce Z….

9. WHAT IS - BUG, DEBUG, DEBUGGING, …
 Debugging is the process of finding and resolving defects
or problems within a computer program that prevent
correct operation of computer software or a system.
 The terms "bug" and "debugging" are popularly
attributed to Admiral Grace Hopper in the 1940s.
 On a Mark II computer at Harvard University, a moth stuck in a
relay and thereby impeding operation, whereupon she remarked
that they were "debugging" the system.
 The term "bug", in the sense of "technical error", dates back at
least to 1878 andThomas Edison (see software bug for a full
discussion).

11. THE PRINCIPLES OF
DEBUGGING

12. THE PRINCIPLES OF DEBUGGING
 Debugging is an art rather than a science
 There are definite principles that guide its practice.
 The Essence of Debugging:The Principle of Confirmation
 The Fundamental Principle of Confirmation
 Fixing a buggy program is a process of confirming, one by one, that the many things
believed to be true about the code are actually true.
 When one of the assumptions is not true, we have found a clue to the location (if not the
exact nature) of a bug.

13. THE PRINCIPLES
OF DEBUGGING
Smart Small
Use a top-down approach
Use a debugging tool to determine the
location of a segmentation fault
Determine the location of an infinite loop by
issuing an interrupt
Use binary search

14. WHY TO USE A TOOL TO
DEBUG?
What is the value of a DebuggingTool for the Principle of
Confirmation?

15. WHYTO USE ATOOLTO DEBUG -TO AVOID…
AddTracing
code
Recompile
Run
Analyze the
trace output
Fix issue
Remove
Tracing code
Whatisthevalueofa
DebuggingToolforthe
PrincipleofConfirmation?

16. WHAT TO EXPECT
OUT OF A DEBUG
TOOL?
What is the value of a DebuggingTool for the Principle of Confirmation?

17. WHATTO EXPECT?
SteppingThrough the Source Code
InspectingVariables
Inspection of changes to aVariable
Moving Up and Down the Call Stack

18. WHATTO EXPECT?
SteppingThrough the Source Code
Breakpoints
Single-stepping
Resume

19.  Debuggers are programs which allow you to
execute your program in a controlled manner,
so you can look inside your program to find a
bug.
 Tools that can examine the state of a running
program.
 Debuggers allow for more fine-tuned control,
and don’t force you to repeatedly re-compile
your code every time you want to test
something new
 Common debuggers: adb, dbx, gdb, kdb, wdb,
xdb, pdb, ...
DEBUGGERS
It’s not a tool to remove bugs!

20. WHAT IS GDB?
 GDB is the GNU Project debugger
 Richard Stallman was the original author of gdb
 GDB can be used to debug programs written in C, C++.
 gdb is a reasonably sophisticated text-based debugger.
 Start your program, specifying anything that might affect its behavior.
 Make your program stop on specified conditions.
 Examine what has happened, when your program has stopped.
 Change things in your program, so you can experiment with correcting the effects
of one bug and go on to learn about another.

21. WHYTO LEARN GDB?
Despite its age, gdb remains an amazingly
versatile and flexible tool
Mastering it can save you huge amounts of
time when trying to debug problems in your
code.

22. USAGE
 Usage
gdb [prog] [core | procID]
 GDB is invoked by running the program gdb.
 Once the debugger is started, GDB reads command until you tell it to exit.
 To exit gdb: quit
 GDB can be started with variety of arguments and options.
 gdb program – one argument, which is an executable file more than
one arguments can be provided
 gdb program core – two arguments, one executable and one core
file
 gdb program 1234 – specify process id as second argument

23. Help from the compiler
Dwarf debug info: type system and
calling conventions
Help from the CPU
watchpoint and instruction-level step-
by-step
Help from the OS
... the rest (access to the
memory/registers + scheduler)
BEHINDTHE SCENE

24. COMPILING FOR DEBUGGING
 In order to debug a program effectively, you need to
generate debugging information when you compile
it.
 Debugging information is stored in the object file; it
describes the data type of each variable or function
and the correspondence between source line
numbers and addresses in the executable code.
 With gcc and g++, this is accomplished using the -g
option.
 This option tells the compiler to insert more information
about data types, etc., so the debugger gets a better
understanding of it.

25.  The .gdinit file is the initialization file for gdb.
 Contain GDB commands to automatically
execute during GDB startup
 ~/.gdbinit - User initialization file.
 It is executed unless user specifiedGDB options -
nx, -n or -nh.
 ./.gdbinit - Initialization file for current directory.
 It may need to be enabled with GDB security
command set auto-load local-gdbinit.
.GDBINIT

26. STARTING GDB…
 Starting GDB: gdb
 Loading the symbol table:
file my_prog
 my_prog is executable file name!
 Exit GDB: quit
 Executing shell commands: shell command args
 Compiling within gdb
 Make is a special case: make args
Start GDB and load the symbol
table in one step:
gdb my_prog

27. GDB COMMAND SHORT-HANDS
 Command names may be truncated if the abbreviation is unambiguous: s (for
step), r (for run)
 UNIX styleTAB completion for the command names.
 Alternative way: complete chars.
Eg.: complete h results in: handle
hbreak
help
 Getting help:
 help (or h) – lists all classes of commands.
 h command - displays a short description of the command

28. RUNNING A PROGRAM
 When gdb starts, the program is not actually running.
It won't run until it is instructed.
 run (or r) -- creates an inferior process that runs your program.
 If there are no execution errors the program will finish and results will be displayed
 In case of error, the GDB will show:
 The line the program has stopped on and
 A short description of what it believes has caused the error
 Redirecting output: run > outfile direct the output to the file outfile.
 "Inferior" is a general term to mean "something that you are using gdb to debug" -- generally a
process or perhaps a kernel running on an emulator or on some other piece of hardware connected
on a serial line.

29. SPECIFYING ARGUMENTS
 As arguments to run: run arg1 arg2 …
 With set args command: set args arg1 arg2 …
 run without arguments uses the same arguments used by the previous run.
 set args without arguments – removes all arguments.
 show args command shows the arguments your program has been started
with.

30. DEBUGGING AN ALREADY-RUNNING PROCESS
 From inside GDB: attach process-id
 Tip: UNIX command ps can be used to obtain the process id
 From outside GDB: gdb my_prog process-id
 The first thing GDB does after arranging to debug the
specified process is to stop it.
 detach – detaches the currently attached process from
the GDB control.
 Detached process continues its own execution.

31. KILLINGTHE INFERIOR PROCESS
 Kill - Kill the child process in which your program
is running under gdb.
 Useful if you wish to recompile and relink your
program, since on many systems it is impossible to
modify an executable file while it is running in a
process.
 In this case, when you next type run, gdb notices
that the file has changed, and reads the symbol
table again (while trying to preserve your current
breakpoint settings).

32. BREAKPOINT
 A break point makes your program stop whenever a certain point in the
program is reached
 Ways to set a break point
 break function - Set a breakpoint at entry to function function
 break offset - Sets a breakpoint some number of lines forward or back from the
position at which execution stopped.
 break line-num - Sets a breakpoint at line line number in the current source file
 break filename:function - Sets a breakpoint at entry to function function found in
file filename. Specifying a file name as well as a function name is superfluous except
when multiple files contain similarly named functions.
 info break - Prints a table of all breakpoints set and not deleted

33. WATCHPOINT
 A watch point is a special breakpoint that stops
your program when the value of an expression
changes
 Ways to set a watch point
 watch expr - Sets a watchpoint for an expression.
 info watchpoints - Prints a table of all watch points
set and not deleted

34. ELIMINATE - BREAKPOINTS ANDWATCHPOINTS
 Eliminate a breakpoint or watchpoint once it has done its job and you no longer
want your program to stop there.
 Based on Location
 clear - Delete any breakpoints at the next
instruction to be executed in the selected
stack frame.
 clear function, clear filename:function -
Delete any breakpoints set at entry to
the function function.
 clear linenum, clear filename:linenum -
Delete any breakpoints set at or within
the code of the specified line.
 Based on number
 delete [breakpoints] [range...] -
Delete the breakpoints or
watchpoints of the breakpoint
ranges specified as arguments.
 If no argument is specified, delete all
breakpoints

35. EXAMININGVARIABLES
 Global variables can be examined from every point in the source file.
 Local variables – can be examined only in their scope or using:
 var - file::variable or function::variable
 The variable type: ptype var
 Current value: print var
 Automatic display:
 display var - adds var to the automatic display list.
 undisplay dnum - Removes var from the automatic display list.
 Specifying the output format (x, o, d, u, t, a, f, and c) :
 print /t var - prints the value of var in binary format

36. STEPPINGTHROUGHTHE PROGRAM
 step [count] – program execution continue to
next source line going into function calls.
 next [count] – program execution continue to
the next source line omitting function calls.
 continue [ignore-count] – resume program execution
 ignore-count allows you to specify a further number of times to
ignore a breakpoint at this location
 until – continue until the next source line in the current stack
frame is reached.
 useful to exit from loops
count - times
step into function; next statement

38. ALTERING EXECUTION
 Returning from a function
 finish - forced return
 return [ret_value] – pops the current stack frame
 Continuing at different address: jump line_num|*address
 Altering the value of a variable: set <var> = <value>
 Proceeding to a specified point: until [line_num|*address |function_name]
 call <function(args)> – Invokes the function

39. Stack
frames are
identified
by their
addresses,
which are
kept in the
frame
pointer
register.
Selecting a
frame:
frame
n|addr
up n
down n
Information
about the
current
frame:
frame -
brief
description
info args -
shows
function
arguments
info locals -
shows local
variables
THE STACK FRAME

40. CONVENIENCEVARIABLES
Automatically created convenience variables
$pc – program
counter
$sp – stack pointer $fp – frame pointer
$ps – processor
status
$_ - contains the
last examined
address
$__ - the value in
the last examined
address
$_exitcode - the
exit code of the
debugged program
Convenience variables are used to store values that you may want to refer later.
Any string preceded by $ is regarded as a convenience variable.
Eg.: $table = *table_ptr

41.  The x command (for “examine”):
 x/nfu addr – specify the number of units (n),
the display format (f) and the unit size (u) of
the memory you want to examine, starting
from the address addr. Unit size can be – b,
h (half), w and g (giant).
 x addr – start printing from the address
addr, others default
EXAMINING MEMORY

42. REGISTERS
Registers names are different for each
machine.
Use info registers to see the names used on
your machine.
info all-registers - Print the names and
values of all registers, including floating-
point and vector registers (in the selected
stack frame).
GDB has four
“standard” registers
names that are
available on most
machines:
Program counter - $pc
Stack pointer - $sp
Frame pointer - $fp
Processor status - $ps

43. info proc – summarize
available information about
the current process.
info proc mappings –
address range accessible in
the program.
info proc times – starting
time, user CPU time and
system CPU time for your
program and its children.
info signals – information
about the system signals
and how GDB handles them.
ADDITIONAL PROCESS INFORMATION

44. THREADS
 info threads - Lists all active threads
 thread <Thread Number> - Switching between threads while debugging
(gdb) info threads
Id Target Id Frame
4 Thread 0x7ffff6fc3700 (LWP 2281) "sample" 0x00007ffff73c34fd in write () at
../sysdeps/unix/syscall-template.S:81
3 Thread 0x7ffff67c2700 (LWP 2282) "sample" __lll_lock_wait_private () at
../sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:95
2 Thread 0x7ffff5fc1700 (LWP 2283) "sample" __lll_lock_wait_private () at
../sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:95
* 1 Thread 0x7ffff7fd0740 (LWP 2277) "sample" __lll_lock_wait_private () at
../sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:95

45. THREADS
 thread apply all bt - Checking Stack trace of all the threads
 The command “thread apply“ applies the specified command to specified
thread ID.
 Specify “all” instead of thread ID to apply the command to all threads.
 To display the stack trace of current thread only use command “bt” i.e.
(gdb) bt
#0 __lll_lock_wait_private () at ../sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:95
#1 0x00007ffff733bb1a in __GI__IO_fwrite (buf=0x7ffff7692970 , size=1, count=11, fp=0xffffffffffffffff) at
iofwrite.c:41
#2 0x00007ffff7b63a66 in std::basic_ostream<char, std::char_traits >& std::__ostream_insert<char,
std::char_traits >(std::basic_ostream<char, std::char_traits >&, char const*, long) () from /usr/lib/x86_64-
linux-gnu/libstdc++.so.6
#3 0x00007ffff7b63e77 in std::basic_ostream<char, std::char_traits >& std::operator<< <std::char_traits
>(std::basic_ostream<char, std::char_traits >&, char const*) () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#4 0x000000000040104f in main () at sample.cpp:23

46. POSTMORTEM DEBUGGING – CORE
 A core file or core dump is a file that records the memory image of a running process
and its process status (register values etc.).
 Its primary use is post-mortem debugging of a program that crashed while it ran outside a
debugger.
 A program that crashes automatically produces a core file, unless this feature is disabled by
the user.
 Occasionally, you may wish to produce a core file of the program you are debugging in
order to preserve a snapshot of its state.
 gdb has a special command for that generate-core-file.
 gcore [file]
 Produce a core dump of the inferior process.The optional argument file specifies
 the file name where to put the core dump. If not specified, the file name defaults to ‘core.pid’,
where pid is the inferior process ID.

47. STL CONTAINERS
 Pretty-printers in Python (Yes gdb support automation with python)
 pretty-printers in the libstdc++ svn repository
 Check-out the latest Python libstdc++ printers to a place on your machine. In a
local directory, do:
svn co svn://gcc.gnu.org/svn/gcc/trunk/libstdc++-v3/python
 Add the following to your ~/.gdbinit.
python
import sys
sys.path.insert(0, '/home/user_name/gdb_printers/python')
from libstdcxx.v6.printers import register_libstdcxx_printers
register_libstdcxx_printers (None)
end

48. info pretty-printer – Shows the
loaded pretty printers
print *(iter._M_current) -To display
the item the iterator points at
STL CONTAINERS

49. STL CONTAINERS
Default
• (gdb) print foo_int_vector
• $1 = {<std::_Vector_base<int,
std::allocator<int> >> = {_M_impl =
{<std::allocator<int>> =
{<__gnu_cxx::new_allocator<int>> =
{<No data fields>}, <No data
fields>}, _M_start = 0x603010,
_M_finish = 0x60301c,
_M_end_of_storage = 0x60301c}}, <No
data fields>}
Pretty Printer
• (gdb) print
some_other_foo_int_vector
• $1 = std::vector of length 2,
capacity 2 = {2, 0}

50. SMART POINTERS
 By default, if we print a std::shared_ptr variable
”foo_h", we could see the contents that the ”foo_h" is
pointing to:
 (gdb) print foo_h
$1 = std::shared_ptr (count 1, weak 0) 0x7f2ba8002740
 (gdb) print (*foo_h._M_ptr) - which would print
the contents

51. REMOTE DEBUGGING WITH GDBSERVER
 On platforms where gdbserver is supported, it is possible to use this tool to
debug your application remotely.
 Useful in situations where the program needs to be run on a target host that is
different from the host used for development
$ gdbserver localhost:4444 program
 Process program created; pid = 5685
 Listening on port 4444
$ gdbserver localhost:4444 –attach 5685
 Process program created; pid = 5685
 Listening on port 4444
Target
• $ gdb program
• (gdb) target remote targethost:4444
• Remote debugging using targethost:4444
• (gdb)
Host (Development)

52. GDB MACROS

53. HELLO WORLD
define hw
print "Hello World"
end
document hw
Prints Hello World
end

54. BASIC FORMAT
define <command>
<code>
end
document <command>
<help text>
end

55. CLEARTHE SCREEN
define cls
shell clear
end
document cls
Clears the screen with a simple command.
end

56. USEFUL GDB MACROS - STL
 gdb-stl-views is a set of GDB macros that can
display the contents of many STL containers.
 source {full_path}stl-views-1.0.3.gdb – Load gdb macros
std::vector<T> -- via pvector command
std::list<T> -- via plist or plist_member command
std::map<T,T> -- via pmap or pmap_member command
std::multimap<T,T> -- via pmap or pmap_member command
std::set<T> -- via pset command
std::multiset<T> -- via pset command
std::deque<T> -- via pdequeue command
std::stack<T> -- via pstack command
std::queue<T> -- via pqueue command
std::priority_queue<T> -- via ppqueue command
std::bitset<n> -- via pbitset command
std::string -- via pstring command
std::widestring -- via pwstring command
Download - https://sourceware.org/gdb/wiki/STLSupport?action=AttachFile&do=get&target=stl-views-1.0.3.gdb

57. GDBTIPS ANDTRICKS
 break +line-num - Break Into A Line Which Is RelativeToThe Current Line
 break * memory address - Break upon matching memory address
 backtrace or info stack - Print backtrace AfterThe breakpoint or at a crash
 finish - Execute a functionToThe end after a breakpoint
 frame - Print the line number in while debugging
 call <function> - Calling functions while debugging

58. GDBTIPS ANDTRICKS
 macro expand <macro(args)> - Expand the macro (Need –E option during
build)
 Debugging a process that call fork system call, you want to continue with the
child or the parent
set follow-fork-mode child/parent
set detach-on-fork on
 Debugging a multithreaded application - while a breakpoint hits, the debugger
will freeze all the threads.
 set non-stop on – Let other threads run

59. GDBTIPS ANDTRICKS
 info locals -View all local variables
 list -- view source
 rbreak -- break on function matching regular expression
 set print object on for polymorphic elements

60. GDB AND REVERSE DEBUGGING
 reverse-continue ('rc') - Continue program being debugged but run it in reverse
 reverse-finish- Execute backward until just before the selected stack frame is called
 reverse-next ('rn’) - Step program backward, proceeding through subroutine calls.
 reverse-nexti ('rni') - Step backward one instruction, but proceed through called
subroutines.
 reverse-step ('rs') - Step program backward until it reaches the beginning of a
previous source line
 reverse-stepi - Step backward exactly one instruction
 set exec-direction (forward/reverse) - Set direction of execution.

61. FEW OTHER
USEFUL
TOOLS

62. RECOMMENDED BOOKS

63. GDB QUICK REFEREN CE G D B Version 4
Essential Commands
gdb program [core] debug program [using coredump core]
b [file:]function
run [arglist]
bt
p expr
c
n
s
set breakpoint at function [in file]
start your program [with arglist]
backtrace: display program stack
display the value of an expression
continue running your program
next line, stepping over function calls
next line, stepping into function calls
Starting G DB
gdb
gdb program
gdb program core
gdb --help
start GDB, with no debugging ftles
begin debugging program
debug coredump core produced by
program
describe command line options
exit GDB; also q or EOF(eg C-d)
Stopping G DB
quit
INTERRUPT (eg C-c) terminate current command, or
send to running process
Getting Help
help
help class
help command
list classes of commands
one-line descriptions for commands in
class
describe command
Executing your Program
run arglist
run
run . . . <inf >outf
k i l l
start your program with arglist
start your program with current argument
list
start your program with input, output
redirected
kill running program
t t y dev
s et args arglist
s et args
show args
use dev as stdin and stdout for next run
specify arglist for next run
specify empty argument list
display argument list
show env
show env var
s et env var string
unset env var
show all environment variables
show value of environment variable var
set environment variable var
remove var from environment
Shell Commands
cd dir
pwd
make . . .
shell cmd
change working directory to dir
Print working directory
call “make”
execute arbitrary shell command string
[ ] surround optional arguments . . . show one or more arguments
§c1998 Free Software Foundation, Inc. Permissions on back
Breakpoints and Watchpoints
set breakpoint at line number [in file]
eg: break main.c:37
set breakpoint at func [in file]
set break at offset lines from current stop
break [file:]line
b [file:]line
break [file:]func
break +offset
break -offset
break *addr
break
break . . . i f expr
cond n [expr]
tbreak . . .
rbreak regex
watch expr
catch event
info break
info watch
set breakpoint at address addr
set breakpoint at next instruction
break conditionally on nonzero expr
new conditional expression on breakpoint
n; make unconditional if no expr
temporary break; disable when reached
break on all functions matching regex
set a watchpoint for expression expr
break at event, which may be catch,
throw, exec, fork, vfork, load, or
unload.
show deftned breakpoints
show deftned watchpoints
clear
clear [file:]fun
clear [file:]line
delete [n]
disable [n]
enable [n]
enable once [n]
enable del [n]
ignore n count
delete breakpoints at next instruction
delete breakpoints at entry to fun()
delete breakpoints on source line
delete breakpoints [or breakpoint n]
disable breakpoints [or breakpoint n]
enable breakpoints [or breakpoint n]
enable breakpoints [or breakpoint n];
disable again when reached
enable breakpoints [or breakpoint n];
delete when reached
ignore breakpoint n, count times
commands n
[silent]
command-list
execute GDB command-list every time
end
breakpoint n is reached. [silent
suppresses default display]
end of command-list
print trace of all frames in stack; or of n
frames—innermost if n>0, outermost if
n<0
select frame number n or frame at address
n; if no n, display current frame
select frame n frames up
select frame n frames down
describe selected frame, or frame at addr
arguments of selected frame
Program Stack
backtrace [n]
bt [n]
frame [n]
up n
down n
info frame [addr]
info args
info locals
info reg [rn]. ..
info all-r eg [rn]
local variables of selected frame register
values [for regs rn] in selected
frame; all-r eg includes floating point
Execution Control
continue running; if count specifted, ignore
this breakpoint next count times
execute until another line reached; repeat
count times if specifted
step by machine instructions rather than
source lines
execute next line, including any function
calls
next machine instruction rather than
source line
run until next instruction (or location)
run until selected stack frame returns
continue [count]
c [count]
step [count]
s [count]
stepi [count]
s i [count]
next [count]
n [count]
nexti [count]
ni [count]
u n til [location]
finish
return [expr] pop selected stack frame without
signal num
jump line
jump *address
s et var=expr
executing [setting return value]
resume execution with signal s (none if 0)
resume execution at specifted line number
or address
evaluate expr without displaying it; use
for altering program variables
Display
print [/f ] [expr]
p [/f ][expr]
x
d
u
o
t
a
c
f
c a ll [/f ] expr
x [/Nuf ] expr
N
u
f
disassem [addr]
show value of expr [or last value $]
according to format f:
hexadecimal
signed decimal
unsigned decimal
octal
binary
address, absolute and relative
character
floating point
like print but does not display void
examine memory at address expr; optional
format spec follows slash
count of how many units to display
unit size; one of
b individual bytes
h halfwords (two bytes)
wwords (four bytes)
g giant words (eight bytes)
printing format. Any print format, or
s null-terminated string
i machine instructions
display memory as machine instructions
Automatic Display
display [/f ] expr show value of expr each time program
stops [according to format f ]
display
undisplay n
disable disp n
enable disp n
info display
display all enabled expressions on list
remove number(s) n from list of
automatically displayed expressions
disable display for expression(s) number n
enable display for expression(s) number n
numbered list of display expressions

64. Expressions
expr
addr@len
file: : nm
{type}addr
$
$n
$$
$$n
$
$
$var
an expression in C, C + + , or Modula-2
(including function calls), or:
an array of len elements beginning at
addr
a variable or function nm deftned in file
read memory at addr as specifted type
most recent displayed value
nth displayed value
displayed value previous to $
nth displayed value back from $
last address examined with x
value at address $
convenience variable; assign any value
show values [n]
show conv
show last 10 values [or surrounding $n]
display all convenience variables
Symbol Table
info address s
info func [regex]
info var [regex]
whatis [expr]
ptype [expr]
ptype type
show where symbol s is stored
show names, types of deftned functions
(all, or matching regex)
show names, types of global variables (all,
or matching regex)
show data type of expr [or $] without
evaluating; ptype gives more detail
describe type, struct, union, or enum
GDB Scripts
source script read, execute GDB commands from ftle
script
define cmd
command-list
end
document cmd
help-text
end
create new GDB command cmd; execute
script deftned by command-list
end of command-list
create online documentation for new GDB
command cmd
end of help-text
Signals
handle signal act
print
noprint
stop
nostop
pass
nopass
info signals
specify GDB actions for signal:
announce signal
be silent for signal
halt execution on signal
do not halt execution
allow your program to handle signal
do not allow your program to see signal
show table of signals, GDB action for each
Debugging Targets
target type param connect to target machine, process, or ftle
help target
attach param
detach
display available targets
connect to another process
release target from GDB control
Controlling G DB
s et param value
show param
set one of GDB’s internal parameters
display current setting of parameter
Parameters understood by s et and show:
complaint limit
confirm on/off
editing on/off
height lpp
language lang
li s t s i z e n
prompt str
radix base
verbose on/off
width cpl
write on/off
number of messages on unusual symbols
enable or disable cautionary queries control
readline command-line editing number of
lines before pause in display Language for
GDB expressions (auto, c or
modula-2)
number of lines shown by l i s t
use str as GDB prompt
octal, decimal, or hex number
representation
control messages when loading symbols
number of characters before line folded
Allow or forbid patching binary, core ftles
(when reopened with exec or core)
groups with the following options:history . ..
h . ..
h exp off/on
h f i l e filename
h size size
h save off/on
print . ..
p . ..
disable/enable readline history expansion
ftle for recording GDB command history
number of commands kept in history list
control use of external ftle for command
history
groups with the following options:
p address on/off print memory addresses in stacks, values p
array off/on compact or attractive format for arrays p
demangl on/off source (demangled) or internal form for
C + + symbols
p asm-dem on/off demangle C + + symbols in machine-
instruction output
p elements limit number of array elements to display
p object on/off
p pretty off/on
p union on/off
p vtbl off/on
print C + + derived types for objects
struct display: compact or indented
display of union members
display of C + + virtual function tables
show commands
show commands n
show commands +
show last 10 commands
show 10 commands around number n
show next 10 commands
Working Files
f i l e [file]
core [file]
exec [file]
symbol [file]
load file
add-sym file addr
info f i le s
path dirs
show path
info share
use file for both symbols and executable;
with no arg, discard both
read file as coredump; or discard
use file as executable only; or discard
use symbol table from file; or discard
dynamically link file and add its symbols
read additional symbols from file,
dynamically loaded at addr
display working ftles and targets in use
add dirs to front of path searched for
executable and symbol ftles
display executable and symbol ftle path
list names of shared libraries currently
loaded
Source Files
d ir names
d ir
show d ir
add directory names to front of source
path
clear source path
show current source path
l i s t
l i s t -
l i s t lines
[file:]num
[file: ]function
+off
-off
*address
l i s t f,l
info line num
info source
info sources
forw regex
rev regex
show next ten lines of source
show previous ten lines
display source surrounding lines, specifted
as:
line number [in named ftle]
beginning of function [in named ftle]
off lines after last printed
off lines previous to last printed
line containing address
from line f to line l
show starting, ending addresses of
compiled code for source line num
show name of current source ftle
list all source ftles in use
search following source lines for regex
search preceding source lines for regex
G DB under GNU Emacs
M-x gdb
C-h m
M-s
M-n
M-i
C-c C-f
M-c
M-u
M-d
C-x &
C-x SPC
run GDB under Emacs
describe GDB mode
step one line (step)
next line (next)
step one instruction (stepi)
ftnish current stack frame (finish)
continue (cont)
up arg frames (up)
down arg frames (down)
copy number from point, insert at end
(in source ftle) set break at point
G DB License
show copying
show warranty
Display GNU General Public License
There is NO W ARRANTY for GDB.
Display full no-warranty statement.
Copyright §c 1991, ’92, ’93, ’98 Free Software Foundation, Inc.
Rol a nd H. Pesch
The author assumes no responsibility for any errors on this card.
This card ma y b e freely distribut ed under t he t er ms of t he G N U
General Public License.
Please contribute t o development of this card by annotating it.
Improvements can b e sent t o bug-gdb@gnu.org.
G D B itself is free software; you are welcome t o distribute copies of it
under t he t er ms of t he G N U General Public License. There is
absolutely no warranty for G D B.

65. QUESTIONS::COMMENTS::SUGGESTIONS

66. ITS ALLYOURS!!
Thank you…
Enjoy the Journey as importantly as the Destination itself!!
SenthilKumar Selvaraj
senkumar@juniper.net
https://www.linkedin.com/in/tiruppursenthil
http://randomstufforganized.wordpress.com/