SHN_ABS by Ciro Santilli 35 Updated +Created
hello_world_len points to the special st_shndx == SHN_ABS == 0xF1FF.
0xF1FF is chosen so as to not conflict with other sections.
st_value == 0xD == 13 which is the value we have stored there on the assembly: the length of the string Hello World!.
This means that relocation will not affect this value: it is a constant.
This is small optimization that our assembler does for us and which has ELF support.
If we had used the address of hello_world_len anywhere, the assembler would not have been able to mark it as SHN_ABS, and the linker would have extra relocation work on it later.
Executable and Linkable Format by Ciro Santilli 35 Updated +Created
For a quick and dirty introduction to the format, see: ELF Hello World Tutorial.
How to report Ubuntu crashes by Ciro Santilli 35 Updated +Created
Their crash system does not have an amazing user interface.
Tested on Ubuntu 21.10.
After something crashes, look under /var/crash for a crash file, which helps to determine which package to report under on Launchpad.
E.g. a file /var/crash/_usr_sbin_gdm3.0.crash makes you want to file the bug under gdm at: bugs.launchpad.net/ubuntu/+source/gdm/+filebug
Then, while reporting the bug, you want to give the developpers access to that .crash file. But you can't publicly upload it because it contains memory dumps and could contain secret information. The way to do it is to look at the ID under:
sudo cat /var/crash/_usr_sbin_gdm3.0.uploaded
Ubuntu's crash report system has already uploaded the .crash for you, so you just have to confirm it and give the ID on the ticket.
You can view a list of all your uploaded errors at:
xdg-open https://errors.ubuntu.com/user/$(sudo cat /var/lib/whoopsie/whoopsie-id)
and each of those contain a link to:
https://errors.ubuntu.com/oops/<.uloaded error id>
which you yourself cannot see.
Running:
sudo apport-unpack /var/crash/_usr_sbin_gdm3.0.crash /tmp/app
splits it up into a few files, but does not make any major improvements.
apport-retrace
sudo apt install apport-retrace
sudo chmod 666 /var/crash/_usr_sbin_gdm3.0.crash
apport-retrace -g /var/crash/_usr_sbin_gdm3.0.crash
opens GDB with the core dump. Debug symbols are supplied as separate packages, which is a really cool idea: so you should be able to download them after the crash to see symbols. askubuntu.com/questions/487222/how-to-install-debug-symbols-for-installed-packages mentions how to install them. Official docs at: wiki.ubuntu.com/DebuggingProgramCrash#Debug_Symbol_Packages
Tried:
echo "deb http://ddebs.ubuntu.com $(lsb_release -cs) main restricted universe multiverse" | sudo tee -a /etc/apt/sources.list.d/ddebs.list
echo -e "deb http://ddebs.ubuntu.com $(lsb_release -cs)-updates main restricted universe multiverse\ndeb http://ddebs.ubuntu.com $(lsb_release -cs)-proposed main restricted universe multiverse" | sudo tee -a /etc/apt/sources.list.d/ddebs.list
sudo apt install ubuntu-dbgsym-keyring
but then sudo apt update fails with:
E: The repository 'http://ddebs.ubuntu.com impish-security Release' does not have a Release file.
Sporadic group by Ciro Santilli 35 Updated +Created
Software engineering by Ciro Santilli 35 Updated +Created
Software engineer by Ciro Santilli 35 Updated +Created
Poet warriors monkeys? Or Code peasants (码农) according to the Chinese.
Ciro Santilli claims to be one of them.
Much like a pianist plays his piano, a software engineer plays his computer.
Differential geometry by Ciro Santilli 35 Updated +Created
Bibliography:
Linux by Ciro Santilli 35 Updated +Created
It ain't perfect, but it's decent enough.
From a technical point of view, it can do anything that Microsoft Windows can. Except being forcefully installed on every non-MacOS 2019 computer you can buy.
Ciro Santilli's conversion to Linux happened around 2012, and was a central part of Ciro Santilli's Open Source Enlightenment, since it fundamentally enables the discovery and contribution to open source software. Because what awesome open source person would waste time porting their amazing projects to closed source OSes?
Ciro's modest nature can be seen as he likes to compare this event Buddha's Great Renunciation.
Particularly interesting in the history of Linux is how it won out over the open competitors that were coming up in the time: MINIX (see the chat) and BSD Operating System that got legally bogged down at the critical growth moment.
Figure 1.
xkcd 619: Supported Features
. Source. This perfectly illustrates Linux development. First features that matter. Then useless features.
Video 1. Source. Just stop whatever you are doing, and watch this right now. "I'm on Linux, bitch, I thought you GNU". Fandom explanations. It is just a shame that the Bill Gates actor looks absolutely nothing like the real gates. Actually, the entire Gates/Jobs parts are good, but not genial. But the Linux one is.
Education level by Ciro Santilli 35 Updated +Created
Linux distribution by Ciro Santilli 35 Updated +Created
Hogwarts by Ciro Santilli 35 Updated +Created
R (programming language) by Ciro Santilli 35 Updated +Created
Ubuntu 23.04 install:
sudo apt install rbase
Hello world:
R -e 'print("hello world")'
Install a package, e.g. Bookdown:
sudo R -e 'install.packages("bookdown")'
Python classes by Ciro Santilli 35 Updated +Created
Austria by Ciro Santilli 35 Updated +Created
Pinned article: ourbigbook/introduction-to-the-ourbigbook-project
Welcome to the OurBigBook Project! Our goal is to create the perfect publishing platform for STEM subjects, and get university-level students to write the best free STEM tutorials ever.
Everyone is welcome to create an account and play with the site: ourbigbook.com/go/register. We belive that students themselves can write amazing tutorials, but teachers are welcome too. You can write about anything you want, it doesn't have to be STEM or even educational. Silly test content is very welcome and you won't be penalized in any way. Just keep it legal!
Video 1.
Intro to OurBigBook
. Source.
We have two killer features:
  1. topics: topics group articles by different users with the same title, e.g. here is the topic for the "Fundamental Theorem of Calculus" ourbigbook.com/go/topic/fundamental-theorem-of-calculus
    Articles of different users are sorted by upvote within each article page. This feature is a bit like:
    • a Wikipedia where each user can have their own version of each article
    • a Q&A website like Stack Overflow, where multiple people can give their views on a given topic, and the best ones are sorted by upvote. Except you don't need to wait for someone to ask first, and any topic goes, no matter how narrow or broad
    This feature makes it possible for readers to find better explanations of any topic created by other writers. And it allows writers to create an explanation in a place that readers might actually find it.
    Figure 1.
    Screenshot of the "Derivative" topic page
    . View it live at: ourbigbook.com/go/topic/derivative
    Video 2.
    OurBigBook Web topics demo
    . Source.
  2. local editing: you can store all your personal knowledge base content locally in a plaintext markup format that can be edited locally and published either:
    • to OurBigBook.com to get awesome multi-user features like topics and likes
    • as HTML files to a static website, which you can host yourself for free on many external providers like GitHub Pages, and remain in full control
    This way you can be sure that even if OurBigBook.com were to go down one day (which we have no plans to do as it is quite cheap to host!), your content will still be perfectly readable as a static site.
    Figure 5. . You can also edit articles on the Web editor without installing anything locally.
    Video 3.
    Edit locally and publish demo
    . Source. This shows editing OurBigBook Markup and publishing it using the Visual Studio Code extension.
    Video 4.
    OurBigBook Visual Studio Code extension editing and navigation demo
    . Source.
  3. https://raw.githubusercontent.com/ourbigbook/ourbigbook-media/master/feature/x/hilbert-space-arrow.png
  4. Infinitely deep tables of contents:
    Figure 6.
    Dynamic article tree with infinitely deep table of contents
    .
    Descendant pages can also show up as toplevel e.g.: ourbigbook.com/cirosantilli/chordate-subclade
All our software is open source and hosted at: github.com/ourbigbook/ourbigbook
Further documentation can be found at: docs.ourbigbook.com
Feel free to reach our to us for any help or suggestions: docs.ourbigbook.com/#contact