_aplusb

aplusb

compile.sh

#! /bin/sh

as sort_exec.s -o sort_exec.o
ld --oformat binary sort_exec.o -o sort_exec.bin

info

~/small žœ ls -al ./sort_exec.bin
-rwxrwxr-x 1 shyo shyo 120 Mar  8 20:19 ./sort_exec.bin*

~/small žœ ./sort_exec.bin list
1
2
2
2
3
5
5
10
28
48
2921
9999
10000
10283

~/small žœ cat list
5
2
3
5
10
28
2
1
48
2
10000
9999
2921
10283

~/small žœ strace ./sort_exec.bin list 2>&1 >/dev/null | head
execve("./sort_exec.bin", ["./sort_exec.bin", "list"], [/* 34 vars */]) = 0
execve("/usr/bin/sort", ["-n", "-n", "list"], NULL) = 0
brk(NULL)                               = 0x24ad000
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
access("/etc/ld.so.preload", R_OK)      = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=163472, ...}) = 0
mmap(NULL, 163472, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f56d4135000
close(3)                                = 0
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)

sort_exec.original.s

    .globl  _start
_start:
    popq    %rbx
    popq    %rbx
    pushq   %rbx
    pushq   %rbx

    movl    $28205, (%rbx)   # "-n"
    movb    $59, %al         # sys_exec
    movl    $.LC0, %edi
    movq    %rsp, %rsi
    syscall

.LC0:
    .string "/usr/bin/sort"

sort_exec.s

	.org 0x000000
 
ehdr:           # Elf64_Ehdr
  	.byte 0x7f
  	.ascii "ELF"

###########################################
start1:
 	popq	%rbx
 	popq	%rbx
 	pushq	%rbx
 	pushq	%rbx
	movl	$28205, (%rbx)

	jmp start4

  	.org 0x10
start1end:
##########################################

  	.word  2         # e_type
  	.word  0x3e      # e_machine

##########################################
start4:
 	movb	$59, %al

	jmp		start5

	.org 0x18
start4end:
##########################################

  	# .long  0x90###1         # e_version
  	.quad  start1    #; e_entry
  	.quad  phdr - ehdr  #; e_phoff


##########################################

start5:
 	movl	$.LC0, %edi
 	movq	%rsp, %rsi
 	syscall

  	.org 0x36
start5end:
##########################################

  	.word  phdrsize  # e_phentsize
  	.word  1         # e_phnum
  	.org 0x40
  	ehdrsize = (. - ehdr)

phdr:           # Elf64_Phdr
	.long  1      # p_type
	.long  5      # p_flags
	.quad  0         # p_offset
	.quad  ehdr        #  p_vaddr

##########################################
start2:
.LC0:
 	.ascii	"/usr/bin"
 

	.org 0x60

start2end:
##########################################
	
	.byte '/', 's', 'o', 'r', 't', 0x0, 0x0, 0x0
	.byte '/', 's', 'o', 'r', 't', 0x0, 0x0, 0x0
	.org 0x70
	phdrsize = 0x38 

	.org 0x78

filesize  = (. - 0x78)