Conflict resolution tool by Ciro Santilli 35 Updated +Created
g4ad.xlarge by Ciro Santilli 35 Updated +Created
It's not a tree, it's actually a DAG by Ciro Santilli 35 Updated +Created
But not every directed acyclic graph is a tree.
Example of a tree (and therefore also a DAG):
5
|
4 7
| |
3 6
|/
2
|
1
Convention in this presentation: arrows implicitly point up, just like in a git log, i.e.:
  • 1 is parent of 2
  • 2 is parent of 3 and 6
  • 3 is parent of 4
and so on.
Example of a DAG that is not a tree:
7
|\
4 6
| |
3 5
|/
2
|
1
This is not a tree because there are two ways to reach 7:
  • 2, 3, 4, 7
  • 2, 5, 6, 7
But we often say "tree" intead of "DAG" in the context of Git because DAG sounds ugly.
Example of a graph that is not a DAG:
6
^
|
3->4
^  |
|  v
2<-5
^
|
1
This one is not acyclic because there is a cycle 2, 3, 4, 5, 2.
Git command by Ciro Santilli 35 Updated +Created
Carbohydrate loading by Ciro Santilli 35 Updated +Created
QEMU.js by Ciro Santilli 35 Updated +Created
Stopped 2019 apparently. Shame. We need something to be upstreamed!
Materials science by Ciro Santilli 35 Updated +Created
SHT_NULL by Ciro Santilli 35 Updated +Created
In index 0, SHT_NULL is mandatory. Are there any other uses for it: stackoverflow.com/questions/26812142/what-is-the-use-of-the-sht-null-section-in-elf ?
Global file structure by Ciro Santilli 35 Updated +Created
An ELF file contains the following parts:
  • ELF header. Points to the position of the section header table and the program header table.
  • Section header table (optional on executable). Each has e_shnum section headers, each pointing to the position of a section.
  • N sections, with N <= e_shnum (optional on executable)
  • Program header table (only on executable). Each has e_phnum program headers, each pointing to the position of a segment.
  • N segments, with N <= e_phnum (only on executable)
The order of those parts is not fixed: the only fixed thing is the ELF header that must be the first thing on the file: Generic docs say:
Although the figure shows the program header table immediately after the ELF header, and the section header table following the sections, actual files may differ. Moreover, sections and segments have no specified order. Only the ELF header has a fixed position in the file.
In pictures: sample object file with three sections:
            +-------------------+
            | ELF header        |---+
+---------> +-------------------+   | e_shoff
|           |                   |<--+
| Section   | Section header 0  |
|           |                   |---+ sh_offset
| Header    +-------------------+   |
|           | Section header 1  |---|--+ sh_offset
| Table     +-------------------+   |  |
|           | Section header 2  |---|--|--+
+---------> +-------------------+   |  |  |
            | Section 0         |<--+  |  |
            +-------------------+      |  | sh_offset
            | Section 1         |<-----+  |
            +-------------------+         |
            | Section 2         |<--------+
            +-------------------+
But nothing (except sanity) prevents the following topology:
            +-------------------+
            | ELF header        |---+ e_shoff
            +-------------------+   |
            | Section 1         |<--|--+
+---------> +-------------------+   |  |
|           |                   |<--+  | sh_offset
| Section   | Section header 0  |      |
|           |                   |------|---------+
| Header    +-------------------+      |         |
|           | Section header 1  |------+         |
| Table     +-------------------+                |
|           | Section header 2  |---+            | sh_offset
+---------> +-------------------+   | sh_offset  |
            | Section 2         |<--+            |
            +-------------------+                |
            | Section 0         |<---------------+
            +-------------------+
But some newbies may prefer PNGs :-)
Figure 1.
ELF Executable and Linkable Format diagram by Ange Albertini
. Source.
Implementations by Ciro Santilli 35 Updated +Created
  • Compiler toolchains generate and read ELF files.
    Sane compilers should use a separate standalone library to do the dirty work. E.g., Binutils uses BFD (in-tree and canonical source).
  • Operating systems read and run ELF files.
    Kernels cannot link to a library nor use the C stlib, so they are more likely to implement it themselves.
    This is the case of the Linux kernel 4.2 which implements it in th file fs/binfmt_elf.c.
Standard output by Ciro Santilli 35 Updated +Created
Ubuntu 20.04 by Ciro Santilli 35 Updated +Created
Ubuntu 24.04 by Ciro Santilli 35 Updated +Created
Tim O'Reilly 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