Ciro Santilli @cirosantilli 37

 Articles (11k) Discussions (26) Comments (64) Follows  Received likes Files

New Updated  Top  Announced  A-Z  Liked  Followed

ELF Hello World Tutorial / .strtab Updated 2025-07-16

Holds strings for the symbol table.

This section has sh_type == SHT_STRTAB.

It is pointed to by sh_link == 5 of the .symtab section.

readelf -x .strtab hello_world.o

outputs:

Hex dump of section '.strtab':
  0x00000000 0068656c 6c6f5f77 6f726c64 2e61736d .hello_world.asm
  0x00000010 0068656c 6c6f5f77 6f726c64 0068656c .hello_world.hel
  0x00000020 6c6f5f77 6f726c64 5f6c656e 005f7374 lo_world_len._st
  0x00000030 61727400                            art.

This implies that it is an ELF level limitation that global variables cannot contain NUL characters.

 Read the full article

ELF Hello World Tutorial / STT_NOTYPE Updated 2025-07-16

 View more

Then come the most important symbols:

Num:    Value          Size Type    Bind   Vis      Ndx Name
  4: 0000000000000000     0 NOTYPE  LOCAL  DEFAULT    1 hello_world
  5: 000000000000000d     0 NOTYPE  LOCAL  DEFAULT  ABS hello_world_len
  6: 0000000000000000     0 NOTYPE  GLOBAL DEFAULT    2 _start

hello_world string is in the .data section (index 1). It's value is 0: it points to the first byte of that section.

_start is marked with GLOBAL visibility since we wrote:

global _start

in NASM. This is necessary since it must be seen as the entry point. Unlike in C, by default NASM labels are local.

 Read the full article

ELF Hello World Tutorial / .text section Updated 2025-07-16

 View more

Now that we've done one section manually, let's graduate and use the readelf -S of the other sections:

  [Nr] Name              Type             Address           Offset
       Size              EntSize          Flags  Link  Info  Align
  [ 2] .text             PROGBITS         0000000000000000  00000210
       0000000000000027  0000000000000000  AX       0     0     16

.text is executable but not writable: if we try to write to it Linux segfaults. Let's see if we really have some code there:

objdump -d hello_world.o

gives:

hello_world.o:     file format elf64-x86-64


Disassembly of section .text:

0000000000000000 <_start>:
   0:       b8 01 00 00 00          mov    $0x1,%eax
   5:       bf 01 00 00 00          mov    $0x1,%edi
   a:       48 be 00 00 00 00 00    movabs $0x0,%rsi
  11:       00 00 00
  14:       ba 0d 00 00 00          mov    $0xd,%edx
  19:       0f 05                   syscall
  1b:       b8 3c 00 00 00          mov    $0x3c,%eax
  20:       bf 00 00 00 00          mov    $0x0,%edi
  25:       0f 05                   syscall

If we grep b8 01 00 00 on the hd, we see that this only occurs at 00000210, which is what the section says. And the Size is 27, which matches as well. So we must be talking about the right section.

This looks like the right code: a write followed by an exit.

The most interesting part is line a which does:

movabs $0x0,%rsi

to pass the address of the string to the system call. Currently, the 0x0 is just a placeholder. After linking happens, it will be modified to contain:

4000ba: 48 be d8 00 60 00 00    movabs $0x6000d8,%rsi

This modification is possible because of the data of the .rela.text section.

 Read the full article

Elliptic geometry Updated 2025-07-16

 Read the full article

Elliptic partial differential equation Updated 2025-07-16

 Read the full article

EMBII Updated 2025-07-16

 View more

One of the dudes from the AtomSea & EMBII Bitcoin-based file upload system.

github.com/embiimob
Real name: likely "Eric Bobby" according to:
- LinkedIn: www.linkedin.com/in/eric-bobby-0ab1b935/
- bitfossil.org/affbac1bfde690c1fabd60812d046c911b2882038a42b18a4d2e7cb50e989604/
According to Figure "Loraine.jpg" however, his mother's name was "Loraine Elizabeth White", so there's some chance his real family name is Mr. White.
However according to bitfossil.org/937f70bf641ccabaf623772367df64bd867ad44c53fd227d01f2662e74aeacbf/ his daughter is Maddy Bobby, so maybe he is actually Bobby.
twitter.com/EMBII4U
- twitter.com/TheAtomSea/status/990318090738196481 sample link
- x.com/EMBII4U/status/1901769408453718146 possibly retired in 2021 after working as a barista
he seems to have been quite interested in natural science at around high school before he decided to waste his life as a crypto artist
- x.com/EMBII4U/status/1936278732760666236:
  I was science student of the year 1992 all because of molecular biology for real
  It's not hard to be Science student of the year in Aberdeen SD
- x.com/EMBII4U/status/1727331097447428199 a love declaration to Marie Curie

Figure 1.

EMBII's usual profile image

. Source.

 Read the full article

Emission theory (vision) Updated 2025-07-16

 View more

It is so mind blowing that people believed in this theory. How can you think that, when you turn on a lamp and then you see? Obviously, the lamp must be emitting something!!!

Then comes along this epic 2002 paper: pubmed.ncbi.nlm.nih.gov/12094435/ "Fundamentally misunderstanding visual perception. Adults' belief in visual emissions". TODO review methods...

 Read the full article

Empty circle control qubit notation Updated 2025-07-16

 View more

Some authors use the convention of:

filled black circle: conventional controlled quantum gate, i.e. operate if control qubit is active
empty (White) circle: operate if control qubit is inactive

 Read the full article

Endosymbiont Updated 2025-07-16

 Read the full article

EngineerGuy Updated 2025-07-16

 View more

www.youtube.com/c/engineerguyvideo

en.wikipedia.org/wiki/William_S._Hammack

Does deliver good concise ideas. Now we need something on the less concise side of it.

 Read the full article

Epistle to the Romans Updated 2025-07-16

 Read the full article

Eppendorf tube Updated 2025-07-16

 Read the full article

Erase SSD securely Updated 2025-07-16

 View more

You can't just shred individual sSD files because SSD writes only at large granularities, so hardware/drivers have to copy stuff around all the time to compact it. This means that leftover copies are left around everywhere.

What you can do however is to erase the entire thing with vendor support, which most hardware has support for. On hardware encrypted disks, you can even just erase the keys:

TODO does shredding the

 Read the full article

Ernest Lawrence Updated 2025-07-16

 View more

1932 Nobel Prize in Physics for cyclotron.

 Read the full article

Esalen Institute Updated 2025-07-16

 Read the full article

Escherichia coli Updated 2025-07-16

 View more

www.cell.com/cell/fulltext/S0092-8674(15)00568-1 2015. Using Genome-scale Models to Predict Biological Capabilities. Edward J. O'Brien, Jonathan M. Monk, Bernhard O. Palsson.
www.quora.com/What-are-some-good-books-on-Escherichia-Coli-E-Coli

Size: 1-2 micrometers long and about 0.25 micrometer in diameter, so: 2 * 0.5 * 0.5 * 10e-18 and thus 0.5 micrometer square.

Reference strain: E. Coli K-12 MG1655.

Genome:

4k genes
5 Mbps
www.ncbi.nlm.nih.gov/genome/167
wget ftp://ftp.ncbi.nlm.nih.gov/genomes/all/GCF/000/005/845/GCF_000005845.2_ASM584v2/GCF_000005845.2_ASM584v2_genomic.fna.gz
wget -O NC_000913.3.fasta 'https://www.ncbi.nlm.nih.gov/search/api/sequence/NC_000913.3/?report=fasta'

Synthesis project: www.sciencemag.org/news/2016/08/biologists-are-close-reinventing-genetic-code-life

Omics modeling: www.ncbi.nlm.nih.gov/pmc/articles/PMC5611438/ Tools for Genomic and Transcriptomic Analysis of Microbes at Single-Cell Level Zixi Chen, Lei Chen, Weiwen Zhang.

Bibliography: