Quick introduction to reverse engineering for beginners

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GCC In all other cases, non-SSE2 code will be executed. GCC may also vectorize in some simple cases 72 , if to use -O3 option and to turn on SSE2 support: -msse2. What we got (GCC 4.4.1): ; f(int, int *, int *, int *) public _Z1fiPiS_S_ _Z1fiPiS_S_ proc near var_18 = dword ptr -18h var_14 = dword ptr -14h var_10 = dword ptr -10h arg_0 = dword ptr 8 arg_4 = dword ptr 0Ch arg_8 = dword ptr 10h arg_C = dword ptr 14h push ebp mov ebp, esp push edi push esi push ebx sub esp, 0Ch mov ecx, [ebp+arg_0] mov esi, [ebp+arg_4] mov edi, [ebp+arg_8] mov ebx, [ebp+arg_C] test ecx, ecx jle short loc_80484D8 cmp ecx, 6 lea eax, [ebx+10h] ja short loc_80484E8 loc_80484C1: ; CODE XREF: f(int,int *,int *,int *)+4B ; f(int,int *,int *,int *)+61 ... xor eax, eax nop lea esi, [esi+0] loc_80484C8: ; CODE XREF: f(int,int *,int *,int *)+36 mov edx, [edi+eax*4] add edx, [esi+eax*4] mov [ebx+eax*4], edx add eax, 1 cmp eax, ecx jnz short loc_80484C8 loc_80484D8: ; CODE XREF: f(int,int *,int *,int *)+17 ; f(int,int *,int *,int *)+A5 add esp, 0Ch xor eax, eax 72 More about GCC vectorization support: http://gcc.gnu.org/projects/tree-ssa/vectorization.html 97
pop ebx pop esi pop edi pop ebp retn ; --------------------------------------------------------------------------align 8 loc_80484E8: ; CODE XREF: f(int,int *,int *,int *)+1F test bl, 0Fh jnz short loc_80484C1 lea edx, [esi+10h] cmp ebx, edx jbe loc_8048578 loc_80484F8: ; CODE XREF: f(int,int *,int *,int *)+E0 lea edx, [edi+10h] cmp ebx, edx ja short loc_8048503 cmp edi, eax jbe short loc_80484C1 loc_8048503: ; CODE XREF: f(int,int *,int *,int *)+5D mov eax, ecx shr eax, 2 mov [ebp+var_14], eax shl eax, 2 test eax, eax mov [ebp+var_10], eax jz short loc_8048547 mov [ebp+var_18], ecx mov ecx, [ebp+var_14] xor eax, eax xor edx, edx nop loc_8048520: ; CODE XREF: f(int,int *,int *,int *)+9B movdqu xmm1, xmmword ptr [edi+eax] movdqu xmm0, xmmword ptr [esi+eax] add edx, 1 paddd xmm0, xmm1 movdqa xmmword ptr [ebx+eax], xmm0 add eax, 10h cmp edx, ecx jb short loc_8048520 mov ecx, [ebp+var_18] mov eax, [ebp+var_10] cmp ecx, eax jz short loc_80484D8 loc_8048547: ; CODE XREF: f(int,int *,int *,int *)+73 lea edx, ds:0[eax*4] add esi, edx add edi, edx 98
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Quick introduction to reverse engin
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1.16 C++ classes . . . . . . . . .
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Preface Here (will be) some of my n
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1.1 Hello, world! Let’s start wit
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1.2 Stack Stack — is one of the m
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(_snprintf() function works just li
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1.3 printf() with several arguments
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1.4 scanf() Now let’s use scanf()
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GCC replaced first printf() call to
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}; return 0; printf ("What you ente
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1.5 Passing arguments via stack Now
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1.6 One more word about results ret
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push OFFSET $SG741 ; ’a
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1.8 switch()/case/default 1.8.1 Few
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1.8.2 A lot of cases If switch() st
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loc_804840C: ; DATA XREF: .rodata:0
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et 0 _main ENDP Nothing very specia
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add esp, 1Ch xor eax, eax ; return
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C/C++ standard defines char type as
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eax=eax+ecx return eax ... and this
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mov eax, ecx imul edx sar edx, 1 mo
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; current stack state: ST(0) = resu
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; in local stack here 8 bytes still
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fld QWORD PTR _a$[esp-4] ; current
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In other words, fnstsw ax / sahf in
Page 51 and 52: 1.13 Arrays Array is just a set of
Page 53 and 54: mov [esp+70h+var_70], eax call _pri
Page 55 and 56: jge SHORT $LN1@main mov ecx, DWORD
Page 57 and 58: ebp 0x15 0x15 esi 0x0 0 edi 0x0 0 e
Page 59 and 60: 1.14 Bit fields A lot of functions
Page 61 and 62: So, let’s download Linux Kernel 2
Page 63: There are some redundant code prese
Page 66 and 67: y 10 just by dropping last digit (3
Page 68 and 69: _key$ = 8 ; size = 4 _len$ = 12 ; s
Page 70 and 71: 1.15 Structures It can be defined t
Page 72 and 73: call DWORD PTR __imp__GetSystemTime
Page 74 and 75: 1.15.4 Fields packing in structure
Page 76 and 77: }; int b; struct outer_struct { cha
Page 78 and 79: }; printf ("stepping=%d\n", tmp->st
Page 80 and 81: call ___printf_chk mov eax, esi shr
Page 82 and 83: mov edx, DWORD PTR _t$[ebp] or edx,
Page 84 and 85: 1.16 C++ classes I placed a C++ cla
Page 86 and 87: push ecx mov DWORD PTR _this$[ebp],
Page 88 and 89: call _ZN1c4dumpEv lea eax, [esp+20h
Page 90 and 91: 1.17 Unions 1.17.1 Pseudo-random nu
Page 92 and 93: xor eax, eax pop esi mov esp, ebp p
Page 94 and 95: Let’s compile it in MSVC 2010 (I
Page 96 and 97: comp() function: public comp comp p
Page 98 and 99: Some compilers can do vectorization
Page 100 and 101: mov ecx, [esp+10h+var_10] mov edx,
Page 104 and 105: add ebx, edx lea esi, [esi+0] loc_8
Page 106 and 107: movdqa xmm1, XMMWORD PTR [ecx+16] a
Page 108 and 109: 1.20 x86-64 It’s a 64-bit extensi
Page 110 and 111: } x40 = a3 | x31; x41 = x24 & ~x37;
Page 112 and 113: or ebx, DWORD PTR _x6$[esp+36] mov
Page 114 and 115: and r11, r8 and rsi, r8 and r10, r1
Page 116 and 117: pop rdi pop rsi ret 0 s1 ENDP Nothi
Page 118 and 119: 2.1 LEA instruction LEA (Load Effec
Page 120 and 121: 2.3 npad It’s an assembler macro
Page 122 and 123: 2.4 Signed number representations T
Page 124 and 125: call function function: .. do somet
Page 126 and 127: 3.2 String Debugging messages are o
Page 128 and 129: .text:3011E91B DD 1E fstp qword ptr
Page 130 and 131: loc_80483F2: pop ebp retn _f endp 4
Page 132 and 133: loc_8048444: loc_8048448: loc_80484
Page 134 and 135: public f2 f2 proc near push ebp mov
Page 136 and 137: loc_804840A: loc_804842E: loc_80484
Page 138 and 139: mov esi, DWORD PTR _k$[esp+16] push
Page 140 and 141: or eax, edx retn f endp 4.1.8 Task
Page 142 and 143: 4.2 Middle level 4.2.1 Task 2.1 Wel
Page 144 and 145: mov [edx+eax], bl mov ebx, edi mov
Page 146 and 147: loc_80485AB: ; CODE XREF: f+1E0 ; f
Page 148 and 149: mov [ecx+eax], dl inc eax cmp ebx,
Page 150 and 151: Chapter 5 Tools ∙ IDA as disassem
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Chapter 7 More examples 147
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.text:00541050 arg_0 = dword ptr 4
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.text:005410F3 .text:005410F3 loc_5
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.text:005411A9 pop ebx .text:005411
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.text:00541249 .text:00541249 next_
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.text:005412FC mov esi, offset cube
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.text:005413DC call _fwrite ; write
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.text:005414A7 push ecx ; Filename
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.text:005413A3 mov ecx, [esp+44h+pa
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.text:00541408 push offset aRb ; "r
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}; }; return; fseek (f, 0, SEEK_END
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.text:005411B5 mov ebp, eax Check f
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.text:0054124C inc ebp .text:005412
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This instruction clears bit, in oth
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.text:005410CD add esp, 40h .text:0
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}; for (i=0; i
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}; tmp[y][z]=get_bit (row, y, z); f
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}; fread (buf, flen, 1, f); fclose
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7.2 SAP client network traffic comp
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.text:64413F68 .text:64413F68 loc_6
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.text:64405171 call dbg .text:64405
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.text:64404FF7 push offset aLogging
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.text:64405113 loc_64405113: .text:
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Now let’s dig deeper and find con
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.text:64411E0B .text:64411E0B loc_6
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Chapter 8 Other things 8.1 Compiler
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Chapter 9 Tasks solutions 9.1 Easy
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9.1.5 Task 1.5 Hint #1: Keep in min
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} 9.1.8 Task 1.8 Solution: two 100*
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#define PUSH(low, high) ((void) ((t
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} } ignore one or both. Otherwise,
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