javiermon

/*
$ LANG=C gcc -g -Wall -Werror socket.c -o socket                                                                                                  
$ ./socket 50.116.14.9 0
START
2013-08-27 21:04:47.762757
socket()
2013-08-27 21:04:47.762859

 Error : Connect Failed Connection refused
2013-08-27 21:04:47.956695

javiermon

/*

$ printf '\1' | od -dAn
Little Endian: 1
Big Endian: 256

*/
#include <inttypes.h>
int main(int argc, char ** argv){
    volatile uint32_t i=0x01234567;

javiermon

#include <stdio.h>
#include <sys/socket.h>
#include <linux/netlink.h>
#include <linux/connector.h>
#include <linux/cn_proc.h>
#include <stdlib.h>
#include <errno.h>

struct __attribute__ ((aligned(NLMSG_ALIGNTO))) nlcn_msg {
  struct nlmsghdr nl_hdr;

javiermon

#include <stdio.h>

void hexDump(char *desc, void *addr, int len) 
{
    int i;
    unsigned char buff[17];
    unsigned char *pc = addr;

    // Output description if given.
    if (desc != NULL)

javiermon

High-level

I want to write about why GDB is a great tool for learning C. At least part of the difficulty in learning C is that the language isn’t as interactive as using Python or Ruby.

TL;DR You can kinda use gdb as a repl for c

What’s the smallest possible program we could debug to learn about pointers?

javiermon

One approximate method is to read /proc/meminfo and check Mapped size (on mine its 52544 kB as of now) 
and then check nr_mapped in /proc/vmstat (on mine its 131136 as of now). Finally PAGE_SIZE = Mapped/nr_mapped.

Sometimes this gives you an accurate value (as in the current example I've quoted) 
and sometimes its approximate but very close.

javiermon

- Download the toochain from http://buildroot.uclibc.org/downloads/

Once downloaded & unpacked:
make menuconfig

Then configure the toolchain, check kernel, uclibc, etc versions:
- kernel version (uname -a)
linux 2.6 (manually specified?)
linux version: 2.6.22
- Kernel & arch:

javiermon

#!/usr/bin/python
# netaddr does this and more:
# >>> import netaddr
# >>> netaddr.EUI('d4:be:d9:23:d5:bf').words

import sys

if len(sys.argv) != 2:
    print "usage %s mac-addr" % sys.argv[0]
    sys.exit(-1)

javiermon

#!/usr/bin/env python

"""Simple HTTP Server With Upload.

This module builds on BaseHTTPServer by implementing the standard GET
and HEAD requests in a fairly straightforward manner.

"""

javiermon

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/types.h>
#include <linux/inotify.h>
#include <signal.h>

#define EVENT_SIZE  ( sizeof (struct inotify_event) )
#define EVENT_BUF_LEN     ( 1024 * ( EVENT_SIZE + 16 ) )