230 lines
12 KiB
Markdown
230 lines
12 KiB
Markdown
# Registers
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## General Purpose
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| Register | Usage |
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|----------|--------------------------------------------|
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| rax | Accumulator for general use and syscall number |
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| eax | Lower 32 bits of rax |
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| ax | Lower 16 bits of rax |
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| al | Lower 8 bits of ax |
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| rbx | Base register |
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| ebx | Lower 32 bits of rbx |
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| bx | Lower 16 bits of rbx |
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| bl | Lower 8 bits of bx |
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| rcx | Counter register (loops) |
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| ecx | Lower 32 bits of rcx |
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| cx | Lower 16 bits of rcx |
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| cl | Lower 8 bits of cx |
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| rdx | Data register |
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| edx | Lower 32 bits of rdx |
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| dx | Lower 16 bits of rdx |
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| dl | Lower 8 bits of dx |
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## Index and Pointer
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| Register | Usage |
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|----------|--------------------------------------------|
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| rsi | Source for data (string operations) |
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| esi | Lower 32 bits of rsi |
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| si | Lower 16 bits of rsi |
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| sil | Lower 8 bits of si |
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| rdi | Destination for data |
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| edi | Lower 32 bits of rdi |
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| di | Lower 16 bits of rdi |
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| dil | Lower 8 bits of di |
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| rsp | Stack pointer |
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| esp | Lower 32 bits of rsp |
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| sp | Lower 16 bits of rsp |
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| spl | Lower 8 bits of sp |
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| rbp | Base pointer for stack frames |
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| ebp | Lower 32 bits of rbp |
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| bp | Lower 16 bits of rbp |
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| bpl | Lower 8 bits of bp |
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## Extended
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| Register | Usage |
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|----------|--------------------------------------------|
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| r8–r15 | Extra general-purpose registers |
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| r8d–r15d | Lower 32 bits of r8–r15 |
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| r8w–r15w | Lower 16 bits of r8–r15 |
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| r8b–r15b | Lower 8 bits of r8–r15 |
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# Data Movement
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| Command | Description |
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|-------------------|------------------------------------------|
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| mov dest, src | Copy data from src to dest |
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| movzx dest, src | Zero-extend src into dest |
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| movsx dest, src | Sign-extend src into dest |
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| lea dest, [addr] | Load effective address into dest |
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| rel addr | Relative address |
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| push src | Push value of src onto the stack |
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| pop dest | Pop value from the stack into dest |
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| pusa | Pushes all registers to the stack |
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| popa | Pops all registers from the stack |
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| xchg dest, src | Exchange values of dest and src |
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| cmovcc dest, src | Conditional move |
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| movs dest, src | Move string |
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| movsb | Move byte from [rsi] to [rdi] |
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| movsw | Move word from [rsi] to [rdi] |
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| movsd | Move doubleword from [rsi] to [rdi] |
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| movsq | Move quadword from [rsi] to [rdi] |
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# Arithmetic
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| Command | Description |
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|-------------------|------------------------------------------|
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| add dest, src | Add src to dest |
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| sub dest, src | Subtract src from dest |
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| imul dest, src | Multiply dest by src (signed) |
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| mul src | Multiply rax by src (result in rdx:rax) |
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| idiv src | Divide rdx:rax by src (quotient in rax, remainder in rdx) |
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| xor dest, src | XOR (useful for clearing, e.g., xor rax, rax) |
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| inc reg | Increment reg by 1 |
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| dec reg | Decrement reg by 1 |
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| adc dest, src | Add with carry |
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| sbb dest, src | Subtract with borrow |
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| neg dest | Negate (two's complement) |
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| div src | Unsigned divide rdx:rax by src |
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| cbw | Convert byte to word |
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| cwd | Convert word to doubleword |
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| cdq | Convert doubleword to quadword |
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| cqo | Convert quadword to octword |
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# Logical
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| Command | Description |
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|-------------------|------------------------------------------|
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| and dest, src | Bitwise AND |
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| or dest, src | Bitwise OR |
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| xor dest, src | Bitwise XOR |
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| not dest | Bitwise NOT |
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| shl dest, imm | Shift bits in dest left by imm |
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| shr dest, imm | Shift bits in dest right by imm |
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| sal dest, imm | Arithmetic shift left |
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| sar dest, imm | Arithmetic shift right |
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| rol dest, imm | Rotate bits left |
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| ror dest, imm | Rotate bits right |
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| rcl dest, imm | Rotate through carry left |
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| rcr dest, imm | Rotate through carry right |
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| test dest, src | Test bits (AND without storing result) |
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# Control Flow
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| Command | Description |
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|-------------------|------------------------------------------|
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| jmp label | Unconditional jump to label |
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| cmp op1, op2 | Compare op1 and op2 |
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| je label | Jump if equal |
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| jne label | Jump if not equal |
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| jg label | Jump if greater (signed) |
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| jl label | Jump if less (signed) |
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| jge label | Jump if greater or equal (signed) |
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| jle label | Jump if less or equal (signed) |
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| ja label | Jump if above (unsigned) |
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| jb label | Jump if below (unsigned) |
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| jae label | Jump if above or equal (unsigned) |
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| jbe label | Jump if below or equal (unsigned) |
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| call label | Call a function at label |
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| ret | Return from a function |
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| loop label | Loop to label |
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| loope label | Loop while equal |
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| loopne label | Loop while not equal |
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| jecxz label | Jump if ecx is zero |
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| jrcxz label | Jump if rcx is zero |
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# Syscall Interface (Linux/macOS)
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| Register | Description |
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|----------|--------------------------------------------------|
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| rax | Syscall number |
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| rdi | First argument |
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| rsi | Second argument |
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| rdx | Third argument |
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| r10 | Fourth argument |
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| r8 | Fifth argument |
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| r9 | Sixth argument |
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# Common Syscall Numbers
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| Syscall | rax | Description |
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|-----------|-----------|--------------------------------------|
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| sys_exit | 0x2000001 | Exit program |
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| sys_write | 0x2000004 | Write to file descriptor |
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| sys_read | 0x2000003 | Read from file descriptor |
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# Stack Manipulation
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| Command | Description |
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|-----------|--------------------------------------------------|
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| push reg | Push register value onto the stack |
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| pop reg | Pop top of stack into register |
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| call addr | Call a subroutine at addr |
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| ret | Return from subroutine |
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| enter imm, imm | Create stack frame |
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| leave | Destroy stack frame |
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# String Operations
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| Command | Description |
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|-----------|--------------------------------------------------|
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| movsb | Move byte from [rsi] to [rdi] |
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| movsw | Move word from [rsi] to [rdi] |
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| movsd | Move doubleword from [rsi] to [rdi] |
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| movsq | Move quadword from [rsi] to [rdi] |
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| stosb | Store byte from al to [rdi] |
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| stosw | Store word from ax to [rdi] |
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| stosd | Store doubleword from eax to [rdi] |
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| stosq | Store quadword from rax to [rdi] |
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| lodsb | Load byte from [rsi] into al |
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| lodsw | Load word from [rsi] into ax |
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| lodsd | Load doubleword from [rsi] into eax |
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| lodsq | Load quadword from [rsi] into rax |
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| scasb | Scan byte in al against [rdi] |
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| scasw | Scan word in ax against [rdi] |
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| scasd | Scan doubleword in eax against [rdi] |
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| scasq | Scan quadword in rax against [rdi] |
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| cmpsb | Compare byte at [rsi] with byte at [rdi] |
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| cmpsw | Compare word at [rsi] with word at [rdi] |
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| cmpsd | Compare doubleword at [rsi] with doubleword at [rdi] |
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| cmpsq | Compare quadword at [rsi] with quadword at [rdi] |
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# Data Definition
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| Command | Description |
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|-----------|--------------------------------------------------|
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| db value | Define byte (1 byte) |
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| dw value | Define word (2 bytes) |
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| dd value | Define doubleword (4 bytes) |
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| dq value | Define quadword (8 bytes) |
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| dt value | Define ten bytes (80 bits) |
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# Examples:
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assembly:
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section .data
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byteVar db 0x1 ; Define a byte variable
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wordVar dw 0x1234 ; Define a word variable
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dwordVar dd 0x12345678 ; Define a doubleword variable
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qwordVar dq 0x123456789ABCDEF0 ; Define a quadword variable
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section .text
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global main
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main:
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mov al, [byteVar] ; Move byteVar into al
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mov ax, [wordVar] ; Move wordVar into ax
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mov eax, [dwordVar] ; Move dwordVar into eax
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mov rax, [qwordVar] ; Move qwordVar into rax
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# Tips for Debugging
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- Use xor rax, rax or mov rax, 0 to zero out rax.
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- Use comments liberally to track which registers hold what values!
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- Step through your code with gdb or an equivalent debugger to watch registers change.
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- If things seem off, double-check your mov, cmp, and syscall logic.
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