# >>>>>>>>>>>>> ELF FILE HEADER <<<<<<<<<<<<<
# All numbers (except in names) are in base sixteen (hexadecimal)
# 00 <- number of bytes listed so far
7F 45 4C 46 # 04 e_ident[EI_MAG]: ELF magic number
01 # 05 e_ident[EI_CLASS]: 1: 32-bit, 2: 64-bit
01 # 06 e_ident[EI_DATA]: 1: little-endian, 2: big-endian
01 # 07 e_ident[EI_VERSION]: ELF header version; must be 1
00 # 08 e_ident[EI_OSABI]: Target OS ABI; should be 0
00 # 09 e_ident[EI_ABIVERSION]: ABI version; 0 is ok for Linux
00 00 00 # 0C e_ident[EI_PAD]: unused, should be 0
00 00 00 00 # 10
02 00 # 12 e_type: object file type; 2: executable
03 00 # 14 e_machine: instruction set architecture; 3: x86, 3E: amd64
01 00 00 00 # 18 e_version: ELF identification version; must be 1
54 80 04 08 # 1C e_entry: memory address of entry point (where process starts)
34 00 00 00 # 20 e_phoff: file offset where program headers begin
00 00 00 00 # 24 e_shoff: file offset where section headers begin
00 00 00 00 # 28 e_flags: 0 for x86
34 00 # 2A e_ehsize: size of this header (34: 32-bit, 40: 64-bit)
20 00 # 2C e_phentsize: size of each program header (20: 32-bit, 38: 64-bit)
01 00 # 2E e_phnum: #program headers
28 00 # 30 e_shentsize: size of each section header (28: 32-bit, 40: 64-bit)
00 00 # 32 e_shnum: #section headers
00 00 # 34 e_shstrndx: index of section header containing section names
# >>>>>>>>>>>>> ELF PROGRAM HEADER <<<<<<<<<<<<<
01 00 00 00 # 38 p_type: segment type; 1: loadable
54 00 00 00 # 3C p_offset: file offset where segment begins
54 80 04 08 # 40 p_vaddr: virtual address of segment in memory (x86: 08048054)
00 00 00 00 # 44 p_paddr: physical address of segment, unspecified by 386 supplement
34 00 00 00 # 48 p_filesz: size in bytes of the segment in the file image ############
34 00 00 00 # 4C p_memsz: size in bytes of the segment in memory; p_filesz <= p_memsz
05 00 00 00 # 50 p_flags: segment-dependent flags (1: X, 2: W, 4: R)
00 10 00 00 # 54 p_align: 1000 for x86
# >>>>>>>>>>>>> PROGRAM SEGMENT <<<<<<<<<<<<<
# Print "Hello, world" repeatedly.
# Linux system calls: man 2 syscalls; man 2 write
# Instructions: Intel Vol 2 Chs 3..5
# Values +rd: Intel Vol 2 Table 3-1
# Opcode map: Intel Vol 2 Table A-2
# 54 INTENTION INSTRUCTION OPCODE
BB 01 00 00 00 # ebx <- 1 (stdout)
B9 7E 80 04 08 # ecx <- buf
BA 0A 00 00 00 # edx <- count
BF 03 00 00 00 # 68 edi <- 5 (loop count)
# Begin
B8 04 00 00 00 # eax <- 4 (write) mov r32, imm32 B8+rd id
CD 80 # syscall int imm8 CD ib
4F # edi <- edi - 1 dec r32 48+rd
75 F6 # 72 jump Begin if nonzero jnz rel8 75 cb
B8 01 00 00 00 # eax <- 1 (exit)
BB 00 00 00 00 # ebx <- 0 (param)
CD 80 # 7E syscall
48 45 4C 4F 20 # "HELO "
57 52 4C 44 0A # 88 "WRLD\n"