Inner source Updated 2025-07-16
If you are going to do closed source, at least do it like this.
Basically the opposite of need to know for software.
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Stack Overflow maximum 200 daily reputation limit Updated 2025-07-16
Why. Why. Why is there no limit to how much I can help, but there is a limit to how many thanks I can get?
At most, limit it to a single answer to avoid highly publicized events, e.g. an answer being shared on Reddit. But across answers? It makes no sense.
The two ways main ways to overcome this limit are the 15 point answer accept reputation and bounties.
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Forsyth-Edwards Notation Updated 2025-07-16
The cool thing about this notation is that is showed to Ciro Santilli that there is more state to a chess game than just the board itself! Notably:plus some other boring draw rules counters.
- whose move it is next
- castling availability
- en passant availability
Linux CLI HOWTO Updated 2025-07-16
Two-photon excitation microscopy Updated 2025-07-16
Two Photon Microscopy by Nemonic NeuroNex (2019)
Source. Shows a prototype of a two-photon electron microscope on an optical table, and describes it in good detail, well done. Erhu piece Updated 2025-07-16
Galilean moons Updated 2025-07-16
Can you imagine when those guys started to see moons in other planets? They must have shat bricks. What better evidence can you have that the geocentric model could be wrong?
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www.nature.com/articles/206757a0 on Nature 181, 662-666. Paywalled as of 2022. Has some nice pictures in it.
Sun Erniang Updated 2025-07-16
Erniang is way more popular than her ranking in the 108 Stars of Destiny.
This is of course in part because she is one of the only 3 108 Stars of Destiny women. But her story about making human mantou is particularly fun!
She's also quite seductive, which gives directors a good opportunity for a bit of fan service. See e.g. kknews.cc/history/6epp2pp.html for a still from The Water Margin showing some good cleavage for example.
ELF Hello World Tutorial ELF header Updated 2025-07-16
Running:outputs:
readelf -h hello_world.oMagic: 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00
Class: ELF64
Data: 2's complement, little endian
Version: 1 (current)
OS/ABI: UNIX - System V
ABI Version: 0
Type: REL (Relocatable file)
Machine: Advanced Micro Devices X86-64
Version: 0x1
Entry point address: 0x0
Start of program headers: 0 (bytes into file)
Start of section headers: 64 (bytes into file)
Flags: 0x0
Size of this header: 64 (bytes)
Size of program headers: 0 (bytes)
Number of program headers: 0
Size of section headers: 64 (bytes)
Number of section headers: 7
Section header string table index: 3Running:outputs:
readelf -h hello_world.outMagic: 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00
Class: ELF64
Data: 2's complement, little endian
Version: 1 (current)
OS/ABI: UNIX - System V
ABI Version: 0
Type: EXEC (Executable file)
Machine: Advanced Micro Devices X86-64
Version: 0x1
Entry point address: 0x4000b0
Start of program headers: 64 (bytes into file)
Start of section headers: 272 (bytes into file)
Flags: 0x0
Size of this header: 64 (bytes)
Size of program headers: 56 (bytes)
Number of program headers: 2
Size of section headers: 64 (bytes)
Number of section headers: 6
Section header string table index: 3Bytes in the object file:
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 |....@.....@.....|Executable:
00000000 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 |.ELF............|
00000010 02 00 3e 00 01 00 00 00 b0 00 40 00 00 00 00 00 |..>.......@.....|
00000020 40 00 00 00 00 00 00 00 10 01 00 00 00 00 00 00 |@...............|
00000030 00 00 00 00 40 00 38 00 02 00 40 00 06 00 03 00 |....@.8...@.....|Structure represented:
# define EI_NIDENT 16
typedef struct {
unsigned char e_ident[EI_NIDENT];
Elf64_Half e_type;
Elf64_Half e_machine;
Elf64_Word e_version;
Elf64_Addr e_entry;
Elf64_Off e_phoff;
Elf64_Off e_shoff;
Elf64_Word e_flags;
Elf64_Half e_ehsize;
Elf64_Half e_phentsize;
Elf64_Half e_phnum;
Elf64_Half e_shentsize;
Elf64_Half e_shnum;
Elf64_Half e_shstrndx;
} Elf64_Ehdr;Manual breakdown:
- 0 0:
EI_MAG=7f 45 4c 46=0x7f 'E', 'L', 'F': ELF magic number - 0 4:
EI_CLASS=02=ELFCLASS64: 64 bit elf - 0 5:
EI_DATA=01=ELFDATA2LSB: little endian data - 0 6:
EI_VERSION=01: format version - 0 7:
EI_OSABI(only in 2003 Update) =00=ELFOSABI_NONE: no extensions. - 0 8:
EI_PAD= 8x00: reserved bytes. Must be set to 0. - On the executable it is
02 00forET_EXEC.Another important possibility for the executable isET_DYNfor PIE executables and shared libraries.ET_DYNtells the Linux kernel that the code is position independent, and can loaded at a random memory location with ASLR. - 1 2:
e_machine=3e 00=62=EM_X86_64: AMD64 architecture - 1 4:
e_version=01 00 00 00: must be 1 - 1 8:
e_entry= 8x00: execution address entry point, or 0 if not applicable like for the object file since there is no entry point.On the executable, it isb0 00 40 00 00 00 00 00. The kernel puts the RIP directly on that value when executing. It can be configured by the linker script or-e. But it will segfault if you set it too low: stackoverflow.com/questions/2187484/why-is-the-elf-execution-entry-point-virtual-address-of-the-form-0x80xxxxx-and-n 40 00 00 00on the executable, i.e. it starts immediately after the ELF header.- 2 8:
e_shoff=407x00=0x40: section header table file offset, 0 if not present. The Intel386 architecture defines no flags; so this member contains zero.
- 3 4:
e_ehsize=40 00: size of this elf header. TODO why this field needed? Isn't the size fixed? 38 00on executable: it is 56 bytes long02 00on executable: there are 2 entries.- 3 A:
e_shentsizeande_shnum=40 00 07 00: section header size and number of entries - 3 E:
e_shstrndx(Section Header STRing iNDeX) =03 00: index of the.shstrtabsection.
Microwave transmission Updated 2025-07-16
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