General RegistersEAX | Accumulator | EBX | Base | ECX | Counter | EDX | Data |
General Registers: specific values are expected when calling the kernel. Pointer-RegistersESP | Stackpointer | EBP | Basepointer | EIP | Instructionpointer |
Index-RegistersESI | Source Index | EDI | Destination Index |
Segment- RegistersECS | Code-Segment | EDS | Data-Segment | ESS | Stack-Segment | EES | Extra-Segment |
NASM Basics-f | filesystem | -g | debugginfos | -o | output |
Compiling a Codenasm -f elf32 -g -o filename.o filename.nasm
ld -o filename filename.o
|
in 64bit Architecture use -f elf64 | | Syscall-Numbers LinuxEAX | Name(EBX, ECX, EDX) | 1 | exit( int) | 2 | fork( pointer) | 3 | read( uint, char*, int) | 4 | write( uint, char*, int) | 5 | open( char *, int, int) |
NASM Code-Sections.text | Code | .data | initialized Data | .bss | uninitialized Data |
Exampleglobal _start
.data
msg db "Hello World",0xa
len equ $-msg
.text
_start:
mov eax, 0x4
mov ebx, 0x1
mov ecx, msg
mov edx, len
int 0x80
exit:
mov eax, 0x1
mov ebx, 0x1
int 0x80
|
Miscint Nr
| call Interrup Nr | call label
| jumps to label | ret
| returns to call | nop
| no operation | lea dest,src
| load effective addr. to dest |
int 0x80 calls the Kernel in Linux
Logical Operationsneg op
| two-Complement | not op
| invert each bit | and dest,source
| dest= dest source | or dest,source
| dest=dest source | xor dest, surce
| dest = dest XOR source |
| | Control / Jumps (signed Int)cmp op1,op2
| Compare op1 with op2 | test op1,op2
| bitwise comparison | jmp dest
| unconditional Jump | je dest
| Jump if equal | jne dest
| Jump if not equal | jz dest
| Jump if zero | jnz dest
| Jump if not zero | jg dest
| Jump if greater | jge dest
| Jump if greater or equal | jl dest
| Jump if less | jle dest
| Jump if less or equal |
For unsigned Integer use ja, jae (above) or jb, jbe (below) Mnemonics Intelmov dest, source
| Moves Data | add dest, value
| Add value to dest | sub dest,value
| Subtract value3 from dest* | inc dest
| Increment dest | dec dest
| Decrement dest | mul src
| Multiply EAX and src | imul dest, source
| dest = dest * source |
General Structure:
[label] mnemonic [operands] [;comment] Stack Operationspush source | Insert Value onto the stack | pop dest | Remove value from stack |
Stack is a LIFO-Storage (Last In First Out) |
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