Assembly
Intel Syntax
- Assembler detects type of symbols (no need to add sigil)
mnemonic destination, source
Arithmetic expressions in square brackets
AT&T Syntax
- Register names have a % prefix
- Literal values have a $ prefix
mnemonic source, destination
The mnemonic has a suffix indicating the size
| suffix | desc |
|---|---|
| q | qword |
| l | lword |
| w | word |
| b | byte |
VASM assembler
http://sun.hasenbraten.de/vasm/
Building
# Build assembler for 68000 with motorola syntax
make CPU=m68k SYNTAX=mot
nasm
# Valid output formats
nasm -hf
# don't preprocess (assemble only)
nasm -a ...
# assemble to raw binary
nasm -f bin
# assemble to ELF64 (Linux)
nasm -f elf64 example.asm
# assemble to macho64 (macOS)
nasm -f macho64 example.asm
; Set to 32-bit
BITS 32
shellcode
Dealing with null bytes
Since strcpy stops at a null byte, you’ll need to adjust your instructions to avoid it
; moving zero into a register
; null byte
mov eax, 0
; no null byte
xor eax, eax