Computer Olympiad Updated +Created
Ah, shame, they are a bit weak.
Gospel of Matthew Updated +Created
The first chapter of the New Testament.
Ben Goertzel Updated +Created
www.reddit.com/r/artificial/comments/b38hbk/what_do_my_fellow_ai_researchers_think_of_ben/ What do my fellow AI researchers think of Ben Goertzel and his research?
.text section Updated +Created
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.
.strtab Updated +Created
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.
.rela.text Updated +Created
Section type: sh_type == SHT_RELA.
Common name: "relocation section".
.rela.text holds relocation data which says how the address should be modified when the final executable is linked. This points to bytes of the text area that must be modified when linking happens to point to the correct memory locations.
Basically, it translates the object text containing the placeholder 0x0 address:
   a:       48 be 00 00 00 00 00    movabs $0x0,%rsi
  11:       00 00 00
to the actual executable code containing the final 0x6000d8:
4000ba: 48 be d8 00 60 00 00    movabs $0x6000d8,%rsi
4000c1: 00 00 00
It was pointed to by sh_info = 6 of the .symtab section.
readelf -r hello_world.o outputs:
Relocation section '.rela.text' at offset 0x3b0 contains 1 entries:
  Offset          Info           Type           Sym. Value    Sym. Name + Addend
00000000000c  000200000001 R_X86_64_64       0000000000000000 .data + 0
The section does not exist in the executable.
The actual bytes are:
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  |................|
The struct represented is:
typedef struct {
    Elf64_Addr  r_offset;
    Elf64_Xword r_info;
    Elf64_Sxword    r_addend;
} Elf64_Rela;
So:
  • 370 0: r_offset = 0xC: address into the .text whose address this relocation will modify
  • 370 8: r_info = 0x200000001. Contains 2 fields:
    • ELF64_R_TYPE = 0x1: meaning depends on the exact architecture.
    • ELF64_R_SYM = 0x2: index of the section to which the address points, so .data which is at index 2.
    The AMD64 ABI says that type 1 is called R_X86_64_64 and that it represents the operation S + A where:
    • S: the value of the symbol on the object file, here 0 because we point to the 00 00 00 00 00 00 00 00 of movabs $0x0,%rsi
    • A: the addend, present in field r_added
    This address is added to the section on which the relocation operates.
    This relocation operation acts on a total 8 bytes.
  • 380 0: r_addend = 0
So in our example we conclude that the new address will be: S + A = .data + 0, and thus the first thing in the data section.
Dynamic linking sections Updated +Created
This program did not have certain dynamic linking related sections because we linked it minimally with ld.
However, if you compile a C hello world with GCC 8.2:
gcc -o main.out main.c
some other interesting sections would appear.
GitLab Updated +Created
GitLab was very important to Ciro because he wanted to base Booktree on it.
Prokaryotic elongation factor Updated +Created
Stanford Research Park Updated +Created
University of Stanford spinout company Updated +Created
University of Cambridge spinout company Updated +Created
Epoch (deep learning) Updated +Created
Batch size (deep learning) Updated +Created
Eukaryotic small ribosome subunit Updated +Created
Eukaryotic large ribosome subunit Updated +Created
University of Oxford exam dates Updated +Created
And translating from their arcane vocabulary:
  • Prelims: first year undergrad
  • Honour school; other years of undergrad, sometimes it includes masters others not which is confusing
  • MPhil, MSc, MSt: masters
Andrew Wiles Updated +Created
Video 1.
Beauty Is Suffering
. Source.
Anyon Updated +Created
The name actually comes from "any". Amazing.
Can only exist in 2D surfaces, not 3D, where fermions and bosons are the only options.
All known anyons are quasiparticles.

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