"Some" about the box

Tuesday, March 2, 2021

perf

How perf works: good link: http://sandsoftwaresound.net/perf/perf-tutorial-hot-spots/

Saturday, February 27, 2021

GDB - How it works?

https://blog.0x972.info/?d=2014/11/13/10/40/50-how-does-a-debugger-work

Friday, December 4, 2020

DOS Attack (Denial Of Service)

https://www.cloudflare.com/learning/ddos/what-is-a-ddos-attack/

A distributed denial-of-service (DDoS) attack is a malicious attempt to disrupt the normal traffic of a targeted server, service or network by overwhelming the target or its surrounding infrastructure with a flood of Internet traffic

From a high level, a DDoS attack is like an unexpected traffic jam clogging up the highway, preventing regular traffic from arriving at its destination.

Thursday, November 5, 2020

Red Zone - Stack Frame (x86-64)

https://devblogs.microsoft.com/oldnewthing/20190111-00/?p=100685

https://eli.thegreenplace.net/2011/09/06/stack-frame-layout-on-x86-64

Kernel Threads

kthreadd (pid = 2) created by kernel (pid = 0) during boot
kthreadd helps in creating other kernel threads which are required to run periodically/asynchronously
"ps" shows kernel threads
Everything under [square bracket] are kernel threads

sw0:FID128:root> ps -eaf

UID PID PPID C STIME TTY TIME CMD

root 1 0 0 01:21 ? 00:00:00 init [5]

root 2 0 0 01:21 ? 00:00:00 [kthreadd]

root 3 2 0 01:21 ? 00:00:00 [ksoftirqd/0]

root 4 2 0 01:21 ? 00:00:00 [kworker/0:0]

All calls from user-space to create a new process (including "create_thread" in kthreadd), will end up in do_fork call which internally calls copy_process

Source: https://subscription.packtpub.com/book/application_development/9781785883057/1/ch01lvl1sec13/kernel-threads

Thursday, August 27, 2020

High Mem vs Low Mem

https://linux-kernel-labs.github.io/refs/heads/master/labs/memory_mapping.html

kmalloc: uses low-memory

vmalloc: uses high-memory

Thursday, May 28, 2020

CSS (Cascading Style Sheets)

https://classroom.udacity.com/courses/ud001/lessons/7473321627/concepts/74276264120923

CSS Tricks: https://css-tricks.com/almanac/

CSS: how the content should look in the webpage (layouts, colors etc)
HTML: the actual contents
[Without CSS, HTML allows basic formatting such as bold, italic etc, but nothing more. To use various layouts, use CSS]
NOTE: without CSS, browser also can apply default styling settings.
Youtube without CSS is something that would look like when the internet connection is slow.

CSS has rule-sets.
And a rule-set is nothing but rules on how to render the tags
For ex: div : {color: blue} => would mean, render everything under 'division' in body in blue color
Hence it has 2 parts: tags and the declarations.
CSS rule-sets are written inside <style></style> tags inside <head> tags
Comments inside CSS is same as C or C++: /* CSS comments */
NOTE: Comments inside html is different
attributes and classes:

p { colors: red }; => will change all the paragraph colors to red.
but if we want to change a particular paragraph (id) or a group of paragraphs (classes) to a color, we need id and classes.
while declaring a tag in <body> include the id (id is similar to a variable in C) or classes (group of tags marked to apply a particular setting)
<p id="site-description">check out my site description</p>
<p class="book-summary another-class">Algorithms</p>

NOTE: an html tag can belong to multiple classes (multiple groups/selectors)

And in CSS styles,

<style>

.book-summary { => classes starts with '.'

colors:red
}

#site-description { => id (variables/attributes) starts with #

colors:pink;
}

Colors:

.sidebars {

color: rgb(0, 0, 225) => blue
color: blue => blue
color: #0000ff => blue
color: #00f => blue (short-hand representation of 0000ff)

Selectors:

Basics: Tags, classes and IDs.
More complex selectors: https://developer.mozilla.org/en-US/docs/Learn/CSS/Building_blocks/Selectors

HTML tags (trees)

Elements Link: https://developer.mozilla.org/en-US/docs/Web/HTML/Element

Each page should contain: head + body
head elements are not displayed; mainly used for title, references, meta-data, CSS-styles etc
Body elements are displayed.
Each page should have only one body
Inside body we can have: divisions, header strings, links, images, buttons, paragraphs, sub-strings, super-strings, spans etc.

divisions: <div></div>: Inside divisions, you can organize header strings, buttons etc. A body can have multiple divisions
header strings: <h1-6> </h1-6>: h1 is the highest
links: <a href="https://www.gmail.com">GMAIL</a>: a means anchor here
images: <img src="https://page-containing-image" alt="some description"> [NOTE: images are similar to links: instead of href, we have src. But images dont have end tags </img>; hence, they are one of type called "void elements"
<figure>and <figcaption>=> can be used along with image to provide figure section
For ex:

<figure>
<img src="local_file.jpg" alt="description">
<figurecaption>Caption for the image which will be displayed below the image</figurecaption>
</figure>

<em></em> => for italic
<strong></strong> => for bold
<ul><li>option1</li><li>option2</li></ul> => unordered list
<ol> with numbers by default
Comments inside html:
NOTE: Comments inside CSS is same as C: /* CSS comment */

Monday, October 7, 2019

Fetching Price of a product online

import requests
from bs4 import BeautifulSoup
import smtplib
import getpass

def get_price():
    ''' the url from which u need the product details '''
    URL = 'https://www.amazon.in/JBL-Splash-Proof-Portable-Wireless-Bluetooth/dp/B0125QA4IO?ref_=Oct_DLandingS_PC_a25847b7_13'
    ''' user-agent involved: search for 'my user agent' in your browser to get this info '''
    headers = {'User-Agent' : 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/75.0.3770.80 Safari/537.36'}

    ''' get the whole page; if u print 'page' it will be nasty and big '''
    page = requests.get(URL, headers = headers)

    ''' parse the page (using html parser) '''
    soup = BeautifulSoup(page.content, 'html.parser')

    ''' find the id (aka variable) used in browser that holds product info '''
    product = soup.find(id = 'productTitle').get_text().strip()

    ''' similarly get the price '''
    price = soup.find(id = 'priceblock_ourprice').get_text().strip()
    print (product)
    print (price)

    ''' some manipulation needed to get the price in value (instead of string) '''
    converted_price = price.strip('₹').strip()
    converted_price = float(converted_price.replace(',', ''))
    print (converted_price)
    return converted_price

def send_mail(mailid, password, current_price):
    ''' get the SMTP object '''
    server = smtplib.SMTP('smtp.gmail.com', 587)

    ''' extended hello '''
    server.ehlo()

    ''' put the smtp connection in tls mode; this to get encrypted connection '''
    server.starttls()
    server.ehlo()

    ''' login using your credentials '''
    server.login(mailid, password)

    #subject = 'Hey, the price fell down to ₹ {}/-'.format(current_price).encode('utf-8')
    #subject = 'Hey, the price fell down to ₹ %s' % (str(current_price)).encode('utf-8')
    subject = 'Hey, the price fell down'
    body = 'Check the amazon link for more details: https://www.amazon.in/JBL-Splash-Proof-Portable-Wireless-Bluetooth/dp/B0125QA4IO?ref_=Oct_DLandingS_PC_a25847b7_13'    msg = f"Subject: {subject}\n\n{body}"    server.sendmail('hkumar.sekar@gmail.com', 'harish.sekar@broadcom.com', msg)

    ''' don't forget to delete the smtp object aka. close connection '''
    server.quit()

    print ("Hey, the price dropped. Mail is sent")

def main():
    mailid = input('Enter your email ID: ')
    p = getpass.getpass()
    current_price = get_price()

    if current_price < 6000:
        send_mail(mailid, p, current_price)

if __name__ == '__main__':
    main()

PROGRAM OUTPUT:
C:\Users\hs411053\PycharmProjects\scraper\venv\Scripts\python.exe C:/Users/hs411053/PycharmProjects/scraper/scraper
Enter your email ID: hkumar.sekar@gmail.com
Password:
JBL Flip 3 Portable Wireless Speaker with Powerful Sound & Mic (Blue)
₹ 5,599.00
5599.0
Hey, the price dropped. Mail is sent

Process finished with exit code 0








And the Mail would have been sent.

Sunday, October 6, 2019

How to Print in Makefile

Source: https://stackoverflow.com/questions/11775733/how-can-i-print-message-in-makefile/11776179

15 # for TRACEGEN
16 include $(MAKEDIR)/Tools.make
17
18 ifeq ($(CONFIG_SOMETHING),y)
19 EXTRA_CFLAGS += -fsanitize=kernel-address
20 $(info ************ TEST VERSION ************)
21 else
22 $(info ************ ELSE VERSION ************)
23 endif

$(info your_text) : Information. This doesn't stop the execution.

$(warning your_text) : Warning. This shows the text as a warning.

$(error your_text) : Fatal Error. This will stop the execution.

To print a variable in Makefile:

18 $(info $$CONFIG_VAR1 is [${CONFIG_VAR1}])

19 $(info $$CONFIG_VAR2 is [${CONFIG_VAR2}])