Reverse Engineering for Beginners

CHAPTER 21. STRUCTURES CHAPTER 21. STRUCTURES

ARM + Optimizing Xcode 4.6.3 (LLVM) (Thumb-2 mode)

Listing 21.22: Optimizing Xcode 4.6.3 (LLVM) (Thumb-2 mode)

var_C = -0xC

PUSH {R7,LR}

MOV R7, SP

SUB SP, SP, #4

MOV R9, R1 ; b

MOV R1, R0 ; a

MOVW R0, #0xF10 ; "a=%d; b=%d; c=%d; d=%d\n"

SXTB R1, R1 ; prepare a

MOVT.W R0, #0

STR R3, [SP,#0xC+var_C] ; place d to stack for printf()

ADD R0, PC ; format-string

SXTB R3, R2 ; prepare c

MOV R2, R9 ; b

BLX _printf

ADD SP, SP, #4

POP {R7,PC}

SXTB(Signed Extend Byte) is analogous toMOVSXin x86. All the rest —just the same.

21.4.3 MIPS.

Listing 21.23: Optimizing GCC 4.4.5 (IDA)
1 f:
2
3 var_18 = -0x18
4 var_10 = -0x10
5 var_4 = -4
6 arg_0 = 0
7 arg_4 = 4
8 arg_8 = 8
9 arg_C = 0xC
10
11 ; $a0=s.a
12 ; $a1=s.b
13 ; $a2=s.c
14 ; $a3=s.d
15 lui $gp, (gnu_local_gp >> 16)
16 addiu $sp, -0x28
17 la $gp, (gnu_local_gp & 0xFFFF)
18 sw $ra, 0x28+var_4($sp)
19 sw $gp, 0x28+var_10($sp)
20 ; prepare byte from 32-bit big-endian integer:
21 sra $t0, $a0, 24
22 move $v1, $a1
23 ; prepare byte from 32-bit big-endian integer:
24 sra $v0, $a2, 24
25 lw $t9, (printf & 0xFFFF)($gp)
26 sw $a0, 0x28+arg_0($sp)
27 lui $a0, ($LC0 >> 16) # "a=%d; b=%d; c=%d; d=%d\n"
28 sw $a3, 0x28+var_18($sp)
29 sw $a1, 0x28+arg_4($sp)
30 sw $a2, 0x28+arg_8($sp)
31 sw $a3, 0x28+arg_C($sp)
32 la $a0, ($LC0 & 0xFFFF) # "a=%d; b=%d; c=%d; d=%d\n"
33 move $a1, $t0
34 move $a2, $v1
35 jalr $t9
36 move $a3, $v0 ; branch delay slot
37 lw $ra, 0x28+var_4($sp)
38 or $at, $zero ; load delay slot, NOP
39 jr $ra
40 addiu $sp, 0x28 ; branch delay slot
41