$ gcc -o hex hex.s
$ ./hex
Usage: ./hex [file]

File: hex.s
# a simple hex viewer for linux

.section .rodata

file_mode:
  .asciz "rb"

ErrorMsg0:
  .asciz "fopen is failed!"

ErrorMsg1:
  .asciz "fseek is failed!"

ErrorMsg2:
  .asciz "malloc is failed!"

ErrorMsg3:
  .asciz "fread is failed!"

ErrUsageMsg:
  .asciz "Usage: ./hex <file>\n"

Print_newline:
  .asciz "\n"

Print_hex:
  .asciz "%02x "

Print_line:
  .asciz "%07x "

.section .text
.globl main
main:
        pushl %ebp
        pushl %esi
        pushl %edi

        cmpl $2, 16(%esp)
        jne ErrUsage

        movl 20(%esp), %eax
        movl 4(%eax), %eax

        subl $16, %esp

        movl $file_mode, 4(%esp)
        pushl %eax
        popl (%esp)
        call fopen
        testl %eax, %eax
        jz Error0
        movl %eax, %ebp

        movl %ebp, (%esp)
        movl $0, 4(%esp)
        movl $2, 8(%esp)
        call fseek
        testl %eax, %eax
        jnz Error1 #on error -1

        movl %ebp, (%esp)
        call ftell
        movl %eax, %ebx
        incl %eax
        movl %eax, (%esp)
        call malloc
        testl %eax, %eax
        jz Error2
        movl %eax, %esi

        movb $0, (%ebx, %esi, 1) # adding string termination NULL

        movl %ebp, (%esp)
        call rewind

        movl %ebp, 12(%esp)
        movl $1, 8(%esp)
        movl %ebx, 4(%esp)
        movl %esi, (%esp)
        call fread
        testl %eax, %eax
        js Error3

# %ebx -> bufsize
# %esi -> buffer
# %edi -> counter

        xorl %edi, %edi

        movl %edi, 4(%esp)
        movl $Print_line, (%esp)
        call printf
        movl %edi, 8(%esp)

loop:   movzbl (%esi, %edi, 1), %eax
        movl %eax, 4(%esp)
        movl $Print_hex, (%esp)
        call printf
        incl %edi

        testl $0xf, %edi
        jnz NoNewline
        movl $Print_newline, (%esp)
        call printf

        addl $0x10, 8(%esp)
        pushl 8(%esp)
        popl 4(%esp)
        movl $Print_line, (%esp)
        call printf

NoNewline:
        cmpl %edi, %ebx
        jnz loop

End0:   movl $Print_newline, (%esp)
        call printf

        movl %ebp, (%esp)
        call fclose

Exit:   movl $0, (%esp)
        call exit

Error0: movl $ErrorMsg0, (%esp)
        call puts
        jmp Exit

Error1: movl $ErrorMsg1, (%esp)
        call puts
        jmp Exit

Error2: movl $ErrorMsg2, (%esp)
        call puts
        jmp Exit

Error3: movl $ErrorMsg3, (%esp)
        call puts
        jmp Exit

ErrUsage:
        movl $ErrUsageMsg, (%esp)
        call printf
        jmp Exit