# >>>>>>>>>>>>> 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
7D 00 00 00     # 48 p_filesz: size in bytes of the segment in the file image ############

00 80 FB 77     # 4C p_memsz: size in bytes of the segment in memory; p_filesz <= p_memsz
07 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 <<<<<<<<<<<<<

# String instructions
# 08048000 Head
# 08048100 ibuf
# 08048200 obuf
# 80000000 end process segments
                # INTENTION             INSTRUCTION         OPCODE          NOTE
# Read:                              54
B8 03 00 00 00  # eax = 3 (read)        mov r32, imm32      B8+rd id
31 DB           # ebx = 0 (stdin)       xor r/m32, r32      31 /r           11 011 011
B9 00 81 04 08  # ecx = ibuf            mov r32, imm32      B8+rd id
BA 00 01 00 00  # edx = count           mov r32, imm32      B8+rd id
CD 80           # syscall               int imm8            CD ib

# Dots:         #                    67
FC              # forward               cld                 FC
89 CE           # esi = ecx (ibuf)      mov r/m32, r32      89 /r           11 001 110
B0 2E           # al = '.'              mov r8, imm8        B0+rb ib
B9 20 00 00 00  # ecx = 20              mov r32, imm32      B8+rd id
BF 00 82 04 08  # edi = obuf            mov r32, imm32      B8+rd id
F3 AA           # write many            rep stos m8         F3 AA       Fill al @edi (ecx)
C6 07 0A        # [edi] = '\n'          mov r/m8, imm8      C6 /0 ib        00 000 111
83 EF 20        # edi -= 20             sub r/m32, imm8     83 /5 ib        11 101 111
B0 20           # al = ' '              mov r8, imm8        B0+rb ib

# esi: ibuf (input pointer)
# edi: obuf (output pointer)

# SkipSpace1:   #                    80
87 FE           # swap esi, edi         xchg r/m32, r32     87 /r           11 111 110
B1 FF           # ecx = FF              mov r8, imm8        B0+rb ib
F3 AE           # skip while ==         repe scas m8        F3 AE       Find non-al @edi
4F              # edi--                 dec r32             48+rb
87 FE           # swap esi, edi         xchg r/m32, r32     87 /r           11 111 110

# esi: ibuf + S01
# edi: obuf

# WordLen1:     #                    89
87 FE           # swap esi, edi         xchg r/m32, r32     87 /r           11 111 110
89 FB           # ebx = edi             mov r/m32, r32      89 /r           11 111 011
F2 AE           # skip while !=         repne scas m8       F2 AE       Find al @edi
4F              # edi--                 dec r32             48+rb
89 F9           # ecx = edi             mov r/m32, r32      89 /r           11 111 001
29 D9           # ecx -= ebx            sub r/m32, r32      29 /r           11 011 001
87 FE           # swap esi, edi         xchg r/m32, r32     87 /r           11 111 110
89 DE           # esi = ebx             mov r/m32, r32      89 /r           11 011 110

# ecx: T1
# esi: ibuf + S01
# edi: obuf

# CopyWord1:    #                    98
F3 A4           # copy                  rep movs m8, m8     F3 A4       esi -> edi (ecx)

# esi: ibuf + S01 + T1
# edi: obuf + T1

# SkipSpace2:   #                    9A
87 FE           # swap esi, edi         xchg r/m32, r32     87 /r           11 111 110
B1 FF           # ecx = FF              mov r8, imm8        B0+rb ib
F3 AE           # skip while ==         repe scas m8        F3 AE       Find non-al @edi
4F              # edi--                 dec r32             48+rb
87 FE           # swap esi, edi         xchg r/m32, r32     87 /r           11 111 110

# esi: ibuf + S01 + T1 + S12
# edi: obuf + T1

# WordLen2:     #                    A3
87 FE           # swap esi, edi         xchg r/m32, r32     87 /r           11 111 110
89 FB           # ebx = edi             mov r/m32, r32      89 /r           11 111 011
F2 AE           # skip while !=         repne scas m8       F2 AE       Find al @edi
4F              # edi--                 dec r32             48+rb
89 F9           # ecx = edi             mov r/m32, r32      89 /r           11 111 001
29 D9           # ecx -= ebx            sub r/m32, r32      29 /r           11 011 001
87 FE           # swap esi, edi         xchg r/m32, r32     87 /r           11 111 110

# ecx: T2
# esi: ibuf + S01 + T1 + S12 + T2
# edi: obuf + T1

4E              # esi--                 dec r32             48+rd
BF 1F 82 04 08  # edi = obuf + 1F       mov r32, imm32      B8+rd id
FD              # backward              std                 FD

# ecx: T2
# esi: ibuf + S01 + T1 + S12 + T2 - 1
# edi: obuf + 20 - 1

# CopyWord2:    #                    B7
F3 A4           # copy                  rep movs m8, m8     F3 A4       esi -> edi (ecx)

# Write:        #                    B9
B8 04 00 00 00  # eax = 4 (write)       mov r32, imm32      B8+rd id
BB 01 00 00 00  # ebx = 1 (stdout)      mov r32, imm32      B8+rd id
B9 00 82 04 08  # ecx = obuf            mov r32, imm32      B8+rd id
BA 21 00 00 00  # edx = count           mov r32, imm32      B8+rd id
CD 80           # syscall               int imm8            CD ib
EB 83           # jump Read          D1 jmp rel8            EB cb