Good animation explaining it: Video "Electron transport chain by HarvardX (2017)".
Experiments to measure it:
The 2019 redefinition of the SI base units defines it precisely and uses it as a measure of charge: en.wikipedia.org/wiki/2019_redefinition_of_the_SI_base_units#Ampere
Extracted from this Stack Overflow answer.
ELF Hello World Tutorial
Ciro Santilli 37 Updated 2025-07-01 +Created 1970-01-01
.data
section by .data
is section 1:00000080 01 00 00 00 01 00 00 00 03 00 00 00 00 00 00 00 |................|
00000090 00 00 00 00 00 00 00 00 00 02 00 00 00 00 00 00 |................|
000000a0 0d 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
000000b0 04 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
- 80 4:
sh_type
=01 00 00 00
:SHT_PROGBITS
: the section content is not specified by ELF, only by how the program interprets it. Normal since a.data
section. - 80 8:
sh_flags
=03
7x00
:SHF_WRITE
andSHF_ALLOC
: www.sco.com/developers/gabi/2003-12-17/ch4.sheader.html#sh_flags, as required from a.data
section - 90 0:
sh_addr
= 8x00
: TODO: standard says:but I don't understand it very well yet.If the section will appear in the memory image of a process, this member gives the address at which the section's first byte should reside. Otherwise, the member contains 0.
- 90 8:
sh_offset
=00 02 00 00 00 00 00 00
=0x200
: number of bytes from the start of the program to the first byte in this section 00000200 48 65 6c 6c 6f 20 77 6f 72 6c 64 21 0a 00 |Hello world!.. |
readelf -x .data hello_world.o
which outputs:Hex dump of section '.data': 0x00000000 48656c6c 6f20776f 726c6421 0a Hello world!.
NASM sets decent properties for that section because it treats.data
magically: www.nasm.us/doc/nasmdoc7.html#section-7.9.2Also note that this was a bad section choice: a good C compiler would put the string in.rodata
instead, because it is read-only and it would allow for further OS optimizations.- a0 8:
sh_link
andsh_info
= 8x 0: do not apply to this section type. www.sco.com/developers/gabi/2003-12-17/ch4.sheader.html#special_sections - b0 0:
sh_addralign
=04
= TODO: why is this alignment necessary? Is it only forsh_addr
, or also for symbols insidesh_addr
? - b0 8:
sh_entsize
=00
= the section does not contain a table. If != 0, it means that the section contains a table of fixed size entries. In this file, we see from thereadelf
output that this is the case for the.symtab
and.rela.text
sections.
- a0 8:
ELF Hello World Tutorial Dynamic linking sections by
Ciro Santilli 37 Updated 2025-07-01 +Created 1970-01-01
ELF Hello World Tutorial Global file structure by
Ciro Santilli 37 Updated 2025-07-01 +Created 1970-01-01
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:
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 :-)
"Specula Melitensis Encyclica," or more simply the "Encyclical of Malta," refers to a document issued by the Catholic Church, specifically related to Malta. However, it is important to clarify that there doesn't seem to be a widely recognized or well-documented encyclical by that precise title that is known in the broader context of Catholic doctrine or encyclical literature.
ELF Hello World Tutorial Index 0 section by
Ciro Santilli 37 Updated 2025-07-01 +Created 1970-01-01
Contained in bytes 0x40 to 0x7F.
The first section is always magic: www.sco.com/developers/gabi/2003-12-17/ch4.sheader.html says:
If the number of sections is greater than or equal to SHN_LORESERVE (0xff00), e_shnum has the value SHN_UNDEF (0) and the actual number of section header table entries is contained in the sh_size field of the section header at index 0 (otherwise, the sh_size member of the initial entry contains 0).
There are also other magic sections detailed in
Figure 4-7: Special Section Indexes
.Florence van Straten is known for her work as a Dutch actress and television presenter. She has appeared in various television shows and films, gaining recognition in the entertainment industry. Additionally, she may have made contributions to Dutch culture through her performances and public appearances. For the most accurate and up-to-date information, it would be best to check recent sources or news articles.
The Glasgow Haskell Compiler (GHC) is a state-of-the-art open-source compiler for the Haskell programming language. Developed primarily by the Glasgow Haskell Compiler team at the University of Glasgow, GHC is the most widely used Haskell compiler and is known for its performance, advanced features, and extensive libraries.
ELF Hello World Tutorial Minimal ELF file by
Ciro Santilli 37 Updated 2025-07-01 +Created 1970-01-01
It is non-trivial to determine what is the smallest legal ELF file, or the smaller one that will do something trivial in Linux.
Some impressive attempts:
Fred Singer (1924–2020) was an American theoretical physicist and a prominent figure in climate change debates. He was known for his work in various fields, including atmospheric physics and environmental science. Singer was a professor emeritus at the University of Virginia and held various positions in academia and government throughout his career. Singer is perhaps best known for his skepticism about the extent and causes of global warming, advocating for a more cautious interpretation of climate data.
Garth Paltridge is an Australian atmospheric scientist known for his work in climate science and his critical views on the prevailing consensus regarding climate change. He has contributed to the field through research, publications, and public commentary. Paltridge has been a vocal advocate for skepticism regarding certain climate change models and policies, and he often emphasizes the complexity of climate systems and the uncertainties that exist in climate projections. His views have sparked discussions and debates within the scientific community and among the public regarding climate change discourse.
Running:gives:
hd hello_world.o
00000000 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 |.ELF............|
00000010 01 00 3e 00 01 00 00 00 00 00 00 00 00 00 00 00 |..>.............|
00000020 00 00 00 00 00 00 00 00 40 00 00 00 00 00 00 00 |........@.......|
00000030 00 00 00 00 40 00 00 00 00 00 40 00 07 00 03 00 |....@.....@.....|
00000040 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
00000080 01 00 00 00 01 00 00 00 03 00 00 00 00 00 00 00 |................|
00000090 00 00 00 00 00 00 00 00 00 02 00 00 00 00 00 00 |................|
000000a0 0d 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
000000b0 04 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
000000c0 07 00 00 00 01 00 00 00 06 00 00 00 00 00 00 00 |................|
000000d0 00 00 00 00 00 00 00 00 10 02 00 00 00 00 00 00 |................|
000000e0 27 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |'...............|
000000f0 10 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
00000100 0d 00 00 00 03 00 00 00 00 00 00 00 00 00 00 00 |................|
00000110 00 00 00 00 00 00 00 00 40 02 00 00 00 00 00 00 |........@.......|
00000120 32 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |2...............|
00000130 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
00000140 17 00 00 00 02 00 00 00 00 00 00 00 00 00 00 00 |................|
00000150 00 00 00 00 00 00 00 00 80 02 00 00 00 00 00 00 |................|
00000160 a8 00 00 00 00 00 00 00 05 00 00 00 06 00 00 00 |................|
00000170 04 00 00 00 00 00 00 00 18 00 00 00 00 00 00 00 |................|
00000180 1f 00 00 00 03 00 00 00 00 00 00 00 00 00 00 00 |................|
00000190 00 00 00 00 00 00 00 00 30 03 00 00 00 00 00 00 |........0.......|
000001a0 34 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |4...............|
000001b0 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
000001c0 27 00 00 00 04 00 00 00 00 00 00 00 00 00 00 00 |'...............|
000001d0 00 00 00 00 00 00 00 00 70 03 00 00 00 00 00 00 |........p.......|
000001e0 18 00 00 00 00 00 00 00 04 00 00 00 02 00 00 00 |................|
000001f0 04 00 00 00 00 00 00 00 18 00 00 00 00 00 00 00 |................|
00000200 48 65 6c 6c 6f 20 77 6f 72 6c 64 21 0a 00 00 00 |Hello world!....|
00000210 b8 01 00 00 00 bf 01 00 00 00 48 be 00 00 00 00 |..........H.....|
00000220 00 00 00 00 ba 0d 00 00 00 0f 05 b8 3c 00 00 00 |............<...|
00000230 bf 00 00 00 00 0f 05 00 00 00 00 00 00 00 00 00 |................|
00000240 00 2e 64 61 74 61 00 2e 74 65 78 74 00 2e 73 68 |..data..text..sh|
00000250 73 74 72 74 61 62 00 2e 73 79 6d 74 61 62 00 2e |strtab..symtab..|
00000260 73 74 72 74 61 62 00 2e 72 65 6c 61 2e 74 65 78 |strtab..rela.tex|
00000270 74 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |t...............|
00000280 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
00000290 00 00 00 00 00 00 00 00 01 00 00 00 04 00 f1 ff |................|
000002a0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
000002b0 00 00 00 00 03 00 01 00 00 00 00 00 00 00 00 00 |................|
000002c0 00 00 00 00 00 00 00 00 00 00 00 00 03 00 02 00 |................|
000002d0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
000002e0 11 00 00 00 00 00 01 00 00 00 00 00 00 00 00 00 |................|
000002f0 00 00 00 00 00 00 00 00 1d 00 00 00 00 00 f1 ff |................|
00000300 0d 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
00000310 2d 00 00 00 10 00 02 00 00 00 00 00 00 00 00 00 |-...............|
00000320 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
00000330 00 68 65 6c 6c 6f 5f 77 6f 72 6c 64 2e 61 73 6d |.hello_world.asm|
00000340 00 68 65 6c 6c 6f 5f 77 6f 72 6c 64 00 68 65 6c |.hello_world.hel|
00000350 6c 6f 5f 77 6f 72 6c 64 5f 6c 65 6e 00 5f 73 74 |lo_world_len._st|
00000360 61 72 74 00 00 00 00 00 00 00 00 00 00 00 00 00 |art.............|
00000370 0c 00 00 00 00 00 00 00 01 00 00 00 02 00 00 00 |................|
00000380 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
00000390
Contains the path to the dynamic loader, i.e.
/lib64/ld-linux-x86-64.so.2
in Ubuntu 18.10. Explained at: stackoverflow.com/questions/8040631/checking-if-a-binary-compiled-with-static/55664341#55664341Gavin Schmidt is a prominent climate scientist known for his work in climate modeling and research. He is the director of the NASA Goddard Institute for Space Studies (GISS) and has contributed significantly to understanding climate change and its impacts. Schmidt is also involved in public communication about climate science, helping to bridge the gap between scientific research and public understanding. He regularly engages in discussions regarding climate policy, predictions, and the importance of addressing climate change.
ELF Hello World Tutorial Section header table by
Ciro Santilli 37 Updated 2025-07-01 +Created 1970-01-01
Array of
Elf64_Shdr
structs.Each entry contains metadata about a given section.
e_shoff
of the ELF header gives the starting position, 0x40 here.So the table takes bytes from 0x40 to
0x40 + 7 + 0x40 - 1
= 0x1FF.Some section names are reserved for certain section types: www.sco.com/developers/gabi/2003-12-17/ch4.sheader.html#special_sections e.g.
.text
requires a SHT_PROGBITS
type and SHF_ALLOC
+ SHF_EXECINSTR
Running:outputs:
readelf -S hello_world.o
There are 7 section headers, starting at offset 0x40:
Section Headers:
[Nr] Name Type Address Offset
Size EntSize Flags Link Info Align
[ 0] NULL 0000000000000000 00000000
0000000000000000 0000000000000000 0 0 0
[ 1] .data PROGBITS 0000000000000000 00000200
000000000000000d 0000000000000000 WA 0 0 4
[ 2] .text PROGBITS 0000000000000000 00000210
0000000000000027 0000000000000000 AX 0 0 16
[ 3] .shstrtab STRTAB 0000000000000000 00000240
0000000000000032 0000000000000000 0 0 1
[ 4] .symtab SYMTAB 0000000000000000 00000280
00000000000000a8 0000000000000018 5 6 4
[ 5] .strtab STRTAB 0000000000000000 00000330
0000000000000034 0000000000000000 0 0 1
[ 6] .rela.text RELA 0000000000000000 00000370
0000000000000018 0000000000000018 4 2 4
Key to Flags:
W (write), A (alloc), X (execute), M (merge), S (strings), l (large)
I (info), L (link order), G (group), T (TLS), E (exclude), x (unknown)
O (extra OS processing required) o (OS specific), p (processor specific)
The
struct
represented by each entry is:typedef struct {
Elf64_Word sh_name;
Elf64_Word sh_type;
Elf64_Xword sh_flags;
Elf64_Addr sh_addr;
Elf64_Off sh_offset;
Elf64_Xword sh_size;
Elf64_Word sh_link;
Elf64_Word sh_info;
Elf64_Xword sh_addralign;
Elf64_Xword sh_entsize;
} Elf64_Shdr;
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!
Intro to OurBigBook
. Source. We have two killer features:
- 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-calculusArticles 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/derivativeVideo 2. OurBigBook Web topics demo. Source. - 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: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.
- 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
Figure 2. You can publish local OurBigBook lightweight markup files to either OurBigBook.com or as a static website.Figure 3. Visual Studio Code extension installation.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. - Infinitely deep tables of contents:
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