I was curious about what exactly our executables contain and why it is not just an executable code itself, but complex, well designed format.
I think explaining every single line in my code with comments would be rather distracting than useful. You can just look at raw bytes and not to dive into details, but if you want to, you can always read the specification.
Each python script creates an ELF object byte-by-byte, either executable or
relocatable. To build relocatable objects at once you can use build-rel.sh
script.
It was not intended to be well-written x86 assembly programs, consider
them as inevitable payload so we can see the result, besides looking at
readelf and objdump output.
Smallest possible (excluding ways in which some structures overlap) executable that just does exit(0).
Simple yet complete hello world program.
Relocatable objects that should be linked together by the linker. Here
rel-swap-n-print uses functions swapcase from rel-swapcase and println
from rel-println. It prints a string, swaps the letter case in it and prints it
again.
- System V ABI (common): https://www.sco.com/developers/gabi/latest/contents.html
- System V ABI (x86-64 specific): https://www.uclibc.org/docs/psABI-x86_64.pdf