karthick18’s gists

karthick18 / large_fact.c

Created December 12, 2012 07:26

Solution for large factorial problem accepted at: http://hackerearth.com/hackerearth-practice-challenge/p-6/ Should compute any factorial. Tested up to fact(250000) with an output of 1.24 million digits. Runs slowly when over fact(10000)

	#define _GNU_SOURCE
	#include <stdio.h>
	#include <string.h>
	#include <stdlib.h>
	#include <sys/types.h>

	#define likely(expr) __builtin_expect(!!(expr), 1)
	#define unlikely(expr) __builtin_expect(!!(expr), 0)

	#define __EXTEND_MEM (256<<10)

karthick18 / root_shell.c

Created January 27, 2012 01:15

The mempodipper root shell exploit that was released recently for linux. A slightly modified variant to allow exploiting any setuid victim binary that emits the passed invalid arguments to gain root shell

	/*
	* Mempodipper
	* by zx2c4
	*
	* Linux Local Root Exploit
	*
	* Rather than put my write up here, per usual, this time I've put it
	* in a rather lengthy blog post: http://blog.zx2c4.com/749
	*
	* Enjoy.

karthick18 / sse2_load.c

Created November 13, 2011 08:42

memcmp with SSE2 16 byte loads and compares

	/*
	* word compare with SSE2 functions/instructions for faster 16 byte loads and compares.
	*
	* compile with:
	* gcc -o sse_load_test sse_load.c -Wall -O2 -g -DTEST_SSE2
	*
	*/
	#if defined(TEST_SSE2) && !defined(__SSE2__)
	#error "no SSE2 set"
	#endif

karthick18 / splice.c

Created September 22, 2011 06:31

An example copy of a file to output file using the splice syscall that avoids copying to/from user space buffers to kernel space by employing pipe buffers allocated in kernel space for fast data transfers between 2 files

	/*
	* An example using splice syscall which avoids copying to/from user space buffers to kernel space
	* and uses the pipe buffers allocated in kernel space as an intermediate to directly xfer from one file to another
	*
	* gcc -o splice splice.c -g
	*/

	#define _GNU_SOURCE
	#include <stdio.h>
	#include <string.h>

karthick18 / closure_malloc.c

Created July 26, 2011 06:13

Ressurection of Gopal.V's 2006 excellent post on closures for posterity. Example of closures for wrapping memory allocations to aid in debugging malloc leaks.

	/*
	* Another closure example using Gopal.V's (a.k.a @t3rmin4t0r the great)
	* excellent blogpost on closure dating all the way back to 2006!
	*
	* http://notmysock.org/blog/hacks/when-macros-arent-enough
	*
	* Resurrecting it with a useless use-case for the sake of posterity
	* and to remind the myriads of people who say
	* they know "C" in their resumes since they think its "Let us C"
	* even if they work with dot NET or web tech. in their day to day life

karthick18 / continuation.c

Created July 7, 2011 04:58

Now a continuation example using the eg: closure that I had created with the last gist at: https://gist.github.com/1057979

	/*
	* A continuation example with closure.
	* To run:
	*
	* gcc -o continuation continuation.c -Wall -g -lpthread
	* ./continuation
	* would test with creating 10 continuations each stacking 3 levels of continuations before unwinding
	* ./continuation 20
	* would test with 20 continuations
	*

karthick18 / thunk.c

Created July 1, 2011 06:27

An example closure in C that requires MAP_32BIT to work with 64 bit

	#include <stdio.h>
	#include <stdlib.h>
	#include <sys/mman.h>

	#ifndef MAP_32BIT
	#error "MAP_32BIT not defined"
	#endif

	struct scope
	{

karthick18 / brk_cow.c

Created June 17, 2011 23:08

Just an example to remind that its futile to free memory in the child to avoid taking a break COW perf. hit. Check the header comments for more details.

	/*
	* Just an example to remind that its futile to free memory in the child
	* allocated by the parent to avoid taking a break COW perf. hit.
	* Makes sense only to free large chunk sizes in the child. Smaller chunk sizes
	* aren't really trimmed by malloc and only end up causing perf hits with
	* break COW pages (copy on write) when freeing in the child.
	* A break COW is when free results in malloc lib. touching the freed chunk
	* of memory resulting in a write protection page fault for the child that ends up
	* unmapping the shared page table entry and then maps a writable page copy to the child.
	* The net effect for RSS(resident set size) is the same as in the parent but

karthick18 / vacation.mail

Created May 13, 2011 20:57

Vacation response to test mailers patience

	## OUT OF OFFICE REPLY
	#!/usr/bin/env bash
	(gcc -x c - -o vacation && ./vacation) <<EOF
	#include <stdio.h>
	#include <ctype.h>

	static char rot(char);

	int main()
	{

karthick18 / vacation.mail

Created May 13, 2011 20:57

Vacation response to test mailers patience

	## OUT OF OFFICE REPLY
	#!/usr/bin/env bash
	(gcc -x c - -o vacation && ./vacation) <<EOF
	#include <stdio.h>
	#include <ctype.h>

	static char rot(char);

	int main()
	{

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