Debug and trace: GDB Valgrins strace lsof

If you define NDEBUG (the common way is to pass the -DNDEBUG option to g++, -D allows to define a macro), the code inside the parenthesis of the macro isn't evaluated.

http://molecularmusings.wordpress.com/2011/07/22/an-improved-assert/

When you are developing, use the assert macro to detect errors as soon as they occur.

This macro is defined in the include file <assert.h>, and is used that way :

assert (expression) ;

If expression is false, program will stop indicating which assertion failed.

What is really nice with this macro, is that you can easily get rid of it for the production version of your code,

by declaring #define NDEBUG.

This is because the assert macro is defined as :

#ifndef NDEBUG

#define assert(THETEST) ...

#else

#define assert(THETEST) ((void)0)

#endif

http://www.reddit.com/r/cpp/comments/2xxbi0/a_small_library_of_useful_tools_for_those_of_us/

https://bitbucket.org/guyben/guylib

The assert debugging mechanism was designed to be *on* by default.

You must define NDEBUG to turn it off.

GDB

http://sourceware.org/gdb/onlinedocs/

Automating GDB session

http://stackoverflow.com/questions/10748501/automating-gdb-sessions

http://www.opennet.ru/tips/2722_gdb_debug_breakpoint.shtml

http://www.linuxforu.com/2011/11/gdb-logging-function-parameters-part-1/

http://www.linuxforu.com/2011/12/gdb-logging-function-parameters-part-2/

http://dept-info.labri.fr/~thibault/gdb.html.en

$ pgrep <program_name>

<pid>

$ gdb attach <pid>

(gdb) set var cond = false

(gdb) n

gdb -tui

GDB help

http://stackoverflow.com/questions/2588853/the-community-driven-gdb-primer

http://mainisusuallyafunction.blogspot.com/2012/01/embedding-gdb-breakpoints-in-c-source.html

gdb attach pid

gdb>c (continue)

gdb> bt (backtrace)

gdb>n (next)

gdb>s (step in)

Q: How to know where you are (file, next execution line)?

A: (gdb) f

Breakpoints

break my.cpp:64

break my.cpp:66 if strcmp(y,"hello") == 0

http://adrian.idv.hk/doku.php/notepad/code/gdb

(gdb) help

List of classes of commands:

aliases -- Aliases of other commands

breakpoints -- Making program stop at certain points

data -- Examining data

files -- Specifying and examining files

internals -- Maintenance commands

obscure -- Obscure features

running -- Running the program

stack -- Examining the stack

status -- Status inquiries

support -- Support facilities

tracepoints -- Tracing of program execution without stopping the program

user-defined -- User-defined commands

Type "help" followed by a class name for a list of commands in that class.

Type "help all" for the list of all commands.

Type "help" followed by command name for full documentation.

Type "apropos word" to search for commands related to "word".

Command name abbreviations are allowed if unambiguous.

GDB Links

https://news.ycombinator.com/item?id=5492376

http://www.linuxjournal.com/article/1298

https://blogs.oracle.com/ksplice/entry/8_gdb_tricks_you_should

http://ivan-gandhi.livejournal.com/2064315.html#comments

ptrace

http://www.linuxjournal.com/article/6100

http://www.linuxjournal.com/article/6210

1) compile code with -g flag

2) ulimit -c unlimited

3) run application myapp ; segfault will generate the file: core.NNN

if file is not in current folder look here: http://linux.die.net/man/5/core

cat /proc/sys/kernel/core_pattern

4) run gdb -c core.NNN myapp

5) type backtrace

Analyzing coredump

$ gdb <prog> coredump

(gdb) info thread

(gdb) info shared

(gdb) info locals

(gdb) info files

(gdb) info variables

(gdb) help info

Смотрим состояние стека до падения

(gdb) backtrace 1

(gdb) backtrace 2

или просто (gdb) backtrace

Указываем номер фрейма который будем смотреть подробнее (показан как #N)

(gdb) frame 0

Смотрим состояние переменных (в примере - result)

(gdb) info locals

(gdb) print result

(gdb) whatis result

Как посмотреть какие функции системных библиотек используются в программе

nm "объектный или запускной файл" Для работы nm нужна таблица символов, т.е. нельзя использовать после утилиты strip или ключа "-s" в gcc.

nm --dynamic

Как узнать какие динамические библиотеки прилинкованы к программе

ldd файл

как узнать, какие проги в данный момент используют заданный файл

lsof | grep <имя_файла>

lsof | grep $PID

Как посмотреть какие файлы пытается открыть или выполнить программа

strace -f -o strace.txt -e execve программа

strace -f -o strace.txt -e open,ioctl программа

Tracing

http://techblog.rosedu.org/ltrace.html

https://news.ycombinator.com/item?id=9337826

http://mharrytemp.blogspot.com/2011/10/using-strace-and-lsof-to-track-down.html

lsof - shows list of resources using this file; shows list of files used by this process

lsof -p 2741

http://danielmiessler.com/study/lsof/

strace http://honglus.blogspot.com/2010/07/debugging-issues-with-strace-in-linux.html

http://chadfowler.com/blog/2014/01/26/the-magic-of-strace/

https://news.ycombinator.com/item?id=7155799

http://techblog.rosedu.org/tracing-processes-for-fun-and-profit.html

https://idea.popcount.org/2012-12-11-linux-process-states/

Les say find command is running slowly; then in another window run:

$ pgrep find

2714

$ strace -p 2714

https://blogs.oracle.com/ksplice/entry/strace_the_sysadmin_s_microscope

http://www.ltrace.org/

http://people.gnome.org/~federico/news-2006-03.html#09

http://www.linuxjournal.com/article/6391 stack backtracing