Python / Django: c

Showing posts with label c. Show all posts

Mar 12, 2016

Using RDTSC instruction that returns CPU TSC (Time Stamp Counter)

Jul 16, 2014

Clewn

Clewn provides Gdb support within Vim - Clewn is a standalone program controlling Vim through a NetBeans interface.

List of default key mappings:

        CTRL-Z  send an interrupt to GDB and the program it is running
        B       info breakpoints
        L       info locals
        A       info args
        S       step
        I       stepi
        CTRL-N  next: next source line, skipping all function calls
        X       nexti
        F       finish
        R       run
        Q       quit
        C       continue
        W       where
        CTRL-U  up: go up one frame
        CTRL-D  down: go down one frame

cursor position: ~
        CTRL-B  set a breakpoint on the line where the cursor is located
        CTRL-E  clear all breakpoints on the line where the cursor is located

mouse pointer position: ~
        CTRL-P  print the value of the variable defined by the mouse pointer
                position
        CTRL-X  print the value that is referenced by the address whose
                value is that of the variable defined by the mouse pointer
                position
        CTRL-K  set a breakpoint at assembly address shown by mouse position
        CTRL-H  clear a breakpoint at assembly address shown by mouse position
        CTRL-J  add the selected variable at mouse position to the watched
                variables window

Note: You can tune Vim behavior when using netBeans keys with the mouse
pointer position, by setting Vim balloondelay to a smaller value than its
default. The following setting has been reported to give better results:

    :set balloondelay=100 ~

Note: After browsing your code, you can always return rapidly to the line of
code where GDB is currently stopped, by using CTRL-U and CTRL-D.

Jun 25, 2014

Read auxv

LD_SHOW_AUXV=1 /bin/true

Jun 24, 2014

Elfutils

https://access.redhat.com/site/documentation/en-US/Red_Hat_Developer_Toolset/1/html/User_Guide/chap-elfutils.html

sudo apt-get install elfutils
eu-readelf --all /lib/x86_64-linux-gnu/libc.so.6

Core dump

Allow core dump
Permanent:

sudo vi /etc/security/limits.conf
#add line
#YOUR_USERNAME     soft    core            1000000

Temporary:

ulimit -c unlimited

Core dump

sleep 30
# Type Control-\
Quit (core dumped)

kill -ABRT <PID>
# 11602 abort (core dumped)

In C

abort()

Core dump misc

cat /proc/sys/kernel/core_pattern
man 5 core
cat /proc/PID/coredump_filter

Apr 29, 2014

Resources that have influenced me as a C programmer

From http://www.reddit.com/r/C_Programming/comments/249cmt/resources_that_have_influenced_me_as_a_c/

http://stackoverflow.com/questions/tagged/c

The GNU C Library Reference. Also commonly available as 'info libc'. It should be read like a book. Really.

The Kernel CodingStyle, has some pretty good advice.

What every programmer should know about memory is very relevant for high-speed processing. This is the LWN article.

Kernel design patterns. Another great LWN link. I always smile a little whenever I use the container_of() macro.

Recursive Make Considered Harmful. Makes a fine beverage when mixed with Autotools.

Gnulib - the GNU Portability Library. Add in small quantities.

GNU C Language Extensions. I try to stay pretty compiler-agnostic, but there are some nifty things here. I would have never known about zero-length arrays if not for this.

Linux Device Drivers, 3rd edition.. Definitely worth reading.

The Linux Programming Interface. Likewise.

K&R Second Edition. Almost forgot this one!

GNU Screen. Nothing specific to C programming, but this utility deserves mention.

More than anything, man pages, 'info libc', reading header files, etc. Ways to look things up without first turning to Google, which often links to low signal-to-noise resources.

Apr 14, 2014

Shared libraries and dynamic linker

cc -g -c prog.c mod1.c mod2.c mod3.c
cc -g -o prog_nolib prog.o mod1.o mod2.o mod3.o

strip(1) - discard symbols from object files.

Static lib:

ar r libdemo.a mod1.o mod2.o mod3.o

ar tv libdemo.a
# rw-rw-r-- 1000/1000 1003352 Apr 14 11:24 2014 mod1.o
# rw-rw-r-- 1000/1000 403352 Apr 14 11:24 2014 mod2.o
# rw-rw-r-- 1000/1000  43352 Apr 14 11:24 2014 mod3.o

cc -g -o prog prog.o libdemo.a
# or
cc -g -o prog prog.o -Lmylibdir -ldemo

./prog

Dinamic lib:

gcc -g -c -fPIC -Wall mod1.c mod2.c mod3.c
gcc -g -shared -o libfoo.so mod1.o mod2.o mod3.o
# or 
gcc -g -fPIC -Wall mod1.c mod2.c mod3.c -shared -o libfoo.so

gcc -g -Wall -o prog prog.c libfoo.so
LD_LIBRARY_PATH=. ./prog

nm(1) - list symbols from object files
readelf(1) - displays information about ELF files
objdump(1) - display information from object files
ldd(1) - print shared library dependencies
ldconfig(1) - configure dynamic linker run-time bindings

nm mod1.o
readelf -s mod1.o

objdump --all-headers libfoo.so
readelf -d libfoo.so

Process shared libs:

cat /proc/PID/maps

Shared libs that prog required:

ldd /usr/sbin/tcpdump
# linux-vdso.so.1 =>  (0x00007fffe17ff000)
# libcrypto.so.1.0.0 => /lib/x86_64-linux-gnu/libcrypto.so.1.0.0 (0x00007ff285828000)
# libpcap.so.0.8 => /usr/lib/x86_64-linux-gnu/libpcap.so.0.8 (0x00007ff2855ed000)
# libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007ff285224000)
# libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007ff285020000)
# libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1 (0x00007ff284e07000)
# /lib64/ld-linux-x86-64.so.2 (0x00007ff28606f000)

Where function defined:

nm -A /usr/lib/lib*.so 2> /dev/null | grep ' crypt$'

All system shared libs:

ldconfig –p
#1768 libs found in cache `/etc/ld.so.cache'
# libzvbi.so.0 (libc6,x86-64) => /usr/lib/x86_64-linux-gnu/libzvbi.so.0
# libzvbi-chains.so.0 (libc6,x86-64) => /usr/lib/x86_64-linux-gnu/libzvbi-chains.so.0
# libzltext.so.0.13 (libc6,x86-64) => /usr/lib/libzltext.so.0.13
# libzlcore.so.0.13 (libc6,x86-64) => /usr/lib/libzlcore.so.0.13
# libzip.so.2 (libc6,x86-64) => /usr/lib/libzip.so.2
#...

Path: LD_LIBRARY_PATH, DT_RPATH, DT_RUNPATH, $ORIGIN

gcc -Wl,-rpath,'$ORIGIN'/lib ...

Run-time symbol resolution:

gcc -g -c -fPIC -Wall -c foo.c
gcc -g -shared -o libfoo.so foo.o
gcc -g -o prog prog.c libfoo.so
LD_LIBRARY_PATH=. ./prog
# main-xyz

Monitoring dynamic linker:

LD_DEBUG=help ./prog
LD_DEBUG=all ./prog

Feb 3, 2014

GCC, DDD

gcc

# -S to output assembly
gcc -O0 -S hello.c
# -masm=intel or -masm=att

ddd

gcc -g -c sample sample.c
ddd sample

ddd --disassemble sample

X86 Registers

Jan 23, 2014

Kernel. Modules, program exec, syscalls, elf

man 2 syscalls

system_call()

strace -e trace=open date
strace -c date

ltrace -T -S rmdir t
ltrace -c -S rmdir t

ldd `which python`

Elf

# view headers, section...
readelf -a a.out
readelf --sections=vmlinux a.out
readelf --dynamic a.out

# disassembly
objdump -M intel -S a.out

# list symbols from object files
nm a.out

# dependencies resolved from this list
cat /proc/kallsyms | grep printk

cat /boot/System.map-3.13.0 | grep printk

stat a.out
file a.out

Modules

# list modules
lsmod

# Modules dependencies
cat /lib/modules/3.12.7/modules.dep | grep vboxdrv
man depmod

# info
modinfo vboxdrv

# view system device information
systool -v -m vboxdrv

struct module
sys_init_module() -> load_module()
sys_delete_module()
request_module()
hello world module

man 2 init_module
man 2 delete_module

# which module loader
cat /proc/sys/kernel/modprobe
sudo sysctl -a | grep modprobe

man modprobe
man insmod
man rmmod

ll /sbin/udevd

udevadm monitor

cat /proc/sys/kernel/taintined
dmesg | grep taint

Jan 11, 2014

MALLOC_CHECK_ and MALLOC_PERTURB_

http://l3net.wordpress.com/2013/06/19/malloc_check_-and-malloc_perturb_/

Recent versions of Linux glibc (2.x) include a a malloc() implementation tunable using environment variables. This allows the user to diagnose allocation problems such as heap corruption, double free etc.

When MALLOC_CHECK_ is set to 3, a diagnostic message is printed on stderr and the program is aborted. A value of 0 disables the diagnostic – see man malloc for more details.

Setting the MALLOC_PERTURB_ environment variable causes the malloc functions in libc to return memory which has been wiped and initialized with the byte value of the environment variable. Setting MALLOC_PERTURB_ to zero disables the feature.

No special arguments need to be passed during program compilation. These diagnostics work on any precompiled programs. Unlike valgrind, the speed of execution is not affected.

export MALLOC_CHECK_=3
export MALLOC_PERTURB_=$(($RANDOM % 255 + 1))

Jan 10, 2014

Valgrind overview: runtime memory checker and a bit more aka использование #valgrind на селе

valgrind --tool=callgrind ls

http://www.youtube.com/watch?v=dKngHt9Cvok

Alleyoop is a Valgrind front-end for the GNOME environment, made by Jeffrey Stedfast.

Jan 22, 2013

21st Century C: C Tips from the New School - Ben Klemens - 2012

https://bitbucket.org/st1tch/21st-century-c

Jan 17, 2013

C code auto formatting

indent -st na.c > na2.c

Jan 11, 2013

Compiling C

-O3 indicates optimization level three, which tries every trick known to build faster code. If, when you run the debugger, you find that too many variables have been optimized out for you to follow what’s going on, then change this to -O0.
-Wall adds compiler warnings. This works for gcc, Clang, and icc. For icc, you might prefer -w1, which displays the compiler’s warnings, but not its remarks.
-Werror your compiler will treat warnings as errors.
-I adds the given path to the include search path, which the compiler searches for header files you #included in your code.
-L adds to the library search path. Order matters:

gcc -I/usr/local/include use_useful.c -o use_useful -L/usr/local/lib -luseful

If you have a file named specific.o that depends on the Libbroad library, and Libbroad depends on Libgeneral, then you will need: gcc specific.o -lbroad -lgeneral
-g adds symbols for debugging.

-std=gnu11 is gcc-specific, and specifies that gcc should allow code conforming to the C11 and POSIX standards

pkg-config

pkg-config --libs gsl libxml-2.0
# -lgsl -lgslcblas -lm -lxml2

pkg-config --cflags gsl libxml-2.0
# -I/usr/include/libxml2

gcc `pkg-config --cflags --libs gsl libxml-2.0` -o specific specific.c
# gcc -I/usr/include/libxml2 -lgsl -lgslcblas -lm -lxml2 -o specific specific.c

Runtime linking

export LD_LIBRARY_PATH=libpath:$LD_LIBRARY_PATH
# or 
LDADD=-Llibpath -Wl,-Rlibpath

Jan 10, 2013

Compiling C from stdin

allheads.h:

#include <math.h>
#include <time.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <gsl/gsl_rng.h>

Paste this onto your command line, or add it to your .bashrc, .zshrc, or wherever applicable:

go_libs="-lm"
go_flags="-g -Wall -include allheads.h -O3"
alias go_c="c99 -xc '-' $go_libs $go_flags"

And now we can use a here document to paste short C programs onto the command line:

go_c << '---'
int main(){printf("Hello from the command line.\n");}
---
# and then run:
./a.out

Jan 7, 2013

Head First C - David Griffiths

Exit status of last program

echo $?

&x - location in memory of x variable

You can also call sizeof for a data type, such as sizeof(int).

You can declare a char pointer as const char * to prevent the code from using it to modify a string.

man strstr
info coreutils 'printf'

Q: But what if I want to pass negative numbers as command-line arguments like set_temperature -c -4? Won’t it think that the 4 is an option, not an argument?

A: In order to avoid ambiguity, you can split your main arguments from the options using --. So you would write set_temperature -c -- -4. getopt() will stop reading options when it sees the --, so the rest of the line will be read as simple arguments.

(./bermuda | ./geo2json) < spooky.csv > output.json

If you genuinely want to share variables, you should declare them in your header file and prefix them with the keyword extern:

extern int passcode;

make takes away a lot of the pain of compiling files. But if you find that even it is not automatic enough, take a look at a tool called autoconf

The make tool can do far, far more than we have space to discuss here. To find out more about make and what it can do for you, visit the GNU Make Manual

Remember: when you're assigning struct variables, you are telling the computer to copy data.

If you use the typedef command, you can normally skip giving the struct a proper name. But in a recursive structure, you need to include a pointer to the same type. C syntax won't let you use the typedef alias, so you need to give the struct a proper name. That's why the struct here is called struct island.

The nm command lists the names that are stored inside the archive.

nm /usr/lib/libruby1.8-static.a

When you bind a socket to a port, the operating system will prevent anything else from rebinding to it for the next 30 seconds or so, and that includes the program that bound the port in the first place. Use reuse option (p. 477)

MUT-EX = MUTually EXclusive.

The make tool knows quite a lot about C compilation, and it can use implicit rules to build files without you telling it exactly how. For example, if you have a file called fred.c, you can compile it without a makefile by typing:

> make fred
cc fred.c -o fred

Purchase at Amazon

https://bitbucket.org/st1tch/head-first-c

Author repository: https://github.com/dogriffiths/HeadFirstC