Elves

.gitignore

elf
object-replacement.char
new-elf

README.md

Evaluate

I preffer to manage my stuff using Guix, see: Installation.

Then:

[env]$ guix shell --container
[env]$ ./elf.sh
[env]$ make new-elf
[env]$ hexdump -C new-elf

Try to copy it to clipboard:

$ xsel -b < new-elf
$ xsel -b | hexdump -C

elf.S

; source: https://nathanotterness.com/2021/10/tiny_elf_modernized.html

[bits 64]
file_load_va: equ 4096 * 40

db 0x7f, 'E', 'L', 'F'
db 2
db 1
db 1
db 0
entry_point:
  xor eax, eax
  inc eax
  mov edi, eax
  jmp code_chunk_2
dw 2
dw 0x3e
dd 1
dq entry_point + file_load_va
dq program_headers_start
code_chunk_2:
  mov esi, file_load_va + message
  xor edx, edx
  mov dl, message_length
  jmp code_chunk_3
db 0
dw 64
dw 0x38
dw 1
; We simply deleted the three two-byte fields that used to be here. The only
; one that mattered, the number of section headers, will still be zero due to
; the upper two bytes of the field at the start of the program header being
; zero.

program_headers_start:
; These next two fields also serve as the final six bytes of the ELF header.
dd 1
dd 5
dq 0
dq file_load_va
code_chunk_3:
  syscall
  mov al, 60
  xor edi, edi
  syscall
dq file_end
dq file_end

message: db `Hello, world!\n`
message_length: equ $ - message

file_end:

elf.sh

#!/bin/sh

make elf
chmod +x elf
exec ./elf

Makefile

elf: elf.S
	nasm -f bin -o elf elf.S

object-replacement.char:
	printf '\xef\xbf\xbc' > object-replacement.char # is U+FFFC in UTF-8

new-elf: elf object-replacement.char
	cat object-replacement.char elf > new-elf

.PHONY: clean
clean:
	rm -f elf object-replacement.char new-elf

manifest.scm

(use-modules
  (guix profiles)
  (guix config)
  (gnu packages base)
  (gnu packages assembly)
  (gnu packages linux))

(packages->manifest
  (list
    gnu-make
    nasm
    util-linux   ; printf
    coreutils))  ; rm