Binary Analysis Patterns

Function Prologue/Epilogue

; Standard prologue
push rbp           ; Save base pointer
mov rbp, rsp       ; Set up stack frame
sub rsp, 0x20      ; Allocate local variables

; Leaf function (no calls)
; May skip frame pointer setup
sub rsp, 0x18      ; Just allocate locals

; Standard epilogue
mov rsp, rbp       ; Restore stack pointer
pop rbp            ; Restore base pointer
ret

; Leave instruction (equivalent)
leave              ; mov rsp, rbp; pop rbp
ret

Calling Conventions

System V AMD64 (Linux, macOS)

; Arguments: RDI, RSI, RDX, RCX, R8, R9, then stack
; Return: RAX (and RDX for 128-bit)
; Caller-saved: RAX, RCX, RDX, RSI, RDI, R8-R11
; Callee-saved: RBX, RBP, R12-R15

; Example: func(a, b, c, d, e, f, g)
mov rdi, [a]       ; 1st arg
mov rsi, [b]       ; 2nd arg
mov rdx, [c]       ; 3rd arg
mov rcx, [d]       ; 4th arg
mov r8, [e]        ; 5th arg
mov r9, [f]        ; 6th arg
push [g]           ; 7th arg on stack
call func

Microsoft x64 (Windows)

; Arguments: RCX, RDX, R8, R9, then stack
; Shadow space: 32 bytes reserved on stack
; Return: RAX

; Example: func(a, b, c, d, e)
sub rsp, 0x28      ; Shadow space + alignment
mov rcx, [a]       ; 1st arg
mov rdx, [b]       ; 2nd arg
mov r8, [c]        ; 3rd arg
mov r9, [d]        ; 4th arg
mov [rsp+0x20], [e] ; 5th arg on stack
call func
add rsp, 0x28

ARM Assembly Patterns

ARM64 (AArch64) Calling Convention

; Arguments: X0-X7
; Return: X0 (and X1 for 128-bit)
; Frame pointer: X29
; Link register: X30

; Function prologue
stp x29, x30, [sp, #-16]!  ; Save FP and LR
mov x29, sp                 ; Set frame pointer

; Function epilogue
ldp x29, x30, [sp], #16    ; Restore FP and LR
ret

ARM32 Calling Convention

; Arguments: R0-R3, then stack
; Return: R0 (and R1 for 64-bit)
; Link register: LR (R14)

; Function prologue
push {fp, lr}
add fp, sp, #4

; Function epilogue
pop {fp, pc}    ; Return by popping PC

Control Flow Patterns

Conditional Branches

; if (a == b)
cmp eax, ebx
jne skip_block
; ... if body ...
skip_block:

; if (a < b) - signed
cmp eax, ebx
jge skip_block    ; Jump if greater or equal
; ... if body ...
skip_block:

; if (a < b) - unsigned
cmp eax, ebx
jae skip_block    ; Jump if above or equal
; ... if body ...
skip_block:

Loop Patterns

; for (int i = 0; i < n; i++)
xor ecx, ecx           ; i = 0
loop_start:
cmp ecx, [n]           ; i < n
jge loop_end
; ... loop body ...
inc ecx                ; i++
jmp loop_start
loop_end:

; while (condition)
jmp loop_check
loop_body:
; ... body ...
loop_check:
cmp eax, ebx
jl loop_body

; do-while
loop_body:
; ... body ...
cmp eax, ebx
jl loop_body

Switch Statement Patterns

; Jump table pattern
mov eax, [switch_var]
cmp eax, max_case
ja default_case
jmp [jump_table + eax*8]

; Sequential comparison (small switch)
cmp eax, 1
je case_1
cmp eax, 2
je case_2
cmp eax, 3
je case_3
jmp default_case

Data Structure Patterns

Array Access

; array[i] - 4-byte elements
mov eax, [rbx + rcx*4]        ; rbx=base, rcx=index

; array[i] - 8-byte elements
mov rax, [rbx + rcx*8]

; Multi-dimensional array[i][j]
; arr[i][j] = base + (i * cols + j) * element_size
imul eax, [cols]
add eax, [j]
mov edx, [rbx + rax*4]

Structure Access

struct Example {
    int a;      // offset 0
    char b;     // offset 4
    // padding  // offset 5-7
    long c;     // offset 8
    short d;    // offset 16
};

; Accessing struct fields
mov rdi, [struct_ptr]
mov eax, [rdi]         ; s->a (offset 0)
movzx eax, byte [rdi+4] ; s->b (offset 4)
mov rax, [rdi+8]       ; s->c (offset 8)
movzx eax, word [rdi+16] ; s->d (offset 16)

Linked List Traversal

; while (node != NULL)
list_loop:
test rdi, rdi          ; node == NULL?
jz list_done
; ... process node ...
mov rdi, [rdi+8]       ; node = node->next (assuming next at offset 8)
jmp list_loop
list_done:

Common Code Patterns

String Operations

; strlen pattern
xor ecx, ecx
strlen_loop:
cmp byte [rdi + rcx], 0
je strlen_done
inc ecx
jmp strlen_loop
strlen_done:
; ecx contains length

; strcpy pattern
strcpy_loop:
mov al, [rsi]
mov [rdi], al
test al, al
jz strcpy_done
inc rsi
inc rdi
jmp strcpy_loop
strcpy_done:

; memcpy using rep movsb
mov rdi, dest
mov rsi, src
mov rcx, count
rep movsb

Arithmetic Patterns

; Multiplication by constant
; x * 3
lea eax, [rax + rax*2]

; x * 5
lea eax, [rax + rax*4]

; x * 10
lea eax, [rax + rax*4]  ; x * 5
add eax, eax            ; * 2

; Division by power of 2 (signed)
mov eax, [x]
cdq                     ; Sign extend to EDX:EAX
and edx, 7              ; For divide by 8
add eax, edx            ; Adjust for negative
sar eax, 3              ; Arithmetic shift right

; Modulo power of 2
and eax, 7              ; x % 8

Bit Manipulation

; Test specific bit
test eax, 0x80          ; Test bit 7
jnz bit_set

; Set bit
or eax, 0x10            ; Set bit 4

; Clear bit
and eax, ~0x10          ; Clear bit 4

; Toggle bit
xor eax, 0x10           ; Toggle bit 4

; Count leading zeros
bsr eax, ecx            ; Bit scan reverse
xor eax, 31             ; Convert to leading zeros

; Population count (popcnt)
popcnt eax, ecx         ; Count set bits

Decompilation Patterns

Variable Recovery

; Local variable at rbp-8
mov qword [rbp-8], rax  ; Store to local
mov rax, [rbp-8]        ; Load from local

; Stack-allocated array
lea rax, [rbp-0x40]     ; Array starts at rbp-0x40
mov [rax], edx          ; array[0] = value
mov [rax+4], ecx        ; array[1] = value

Function Signature Recovery

; Identify parameters by register usage