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The ELF standard specifies multiple file formats:
- Object files (
.o
).Intermediate step to generating executables and other formats:Source code | | Compilation | v Object file | | Linking | v Executable
Object files exist to make compilation faster: withmake
, we only have to recompile the modified source files based on timestamps.
- Executable files (no standard Linux extension).This is what the Linux kernel can actually run.
- Archive files (
.a
).Libraries meant to be embedded into executables during the Linking step.
- Shared object files (
.so
).Libraries meant to be loaded when the executable starts running.
- Core dumps.Such files may be generated by the Linux kernel when the program does naughty things, e.g. segfault.They exist to help debugging the program.
In this tutorial, we consider only object and executable files.
This is likely the easiest one to produce as the frequencies are lower, which is why it was discovered first. TODO original setup.
Also because it is transparent to brick and glass, (though not metal) it becomes good for telecommunication.
Some notable subranges:
420 to 680 nm for sure, but larger ranges are observable in laboratory conditions.
Some mechanics:
- inter agent communication
- compute power is limited by limiting Java bytecode count execution per bot per cycle
Battlecode Final Tournament 2023
. Source. Introduction to Battlecode by MIT OpenCourseWare (2014)
Source. 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?
Schematic of the Davisson-Germer experiment
. Source. The first chapter of the New Testament.
Direct consequence of Euclid's formula.
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:to the actual executable code containing the final 0x6000d8:
a: 48 be 00 00 00 00 00 movabs $0x0,%rsi
11: 00 00 00
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 type1
is calledR_X86_64_64
and that it represents the operationS + A
where:This address is added to the section on which the relocation operates. - 380 0:
r_addend
= 0
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