Constraint 1: Position Independence

• The attacker rarely knows the exact address where the payload lands — stack addresses shift with environment and ASLR.
• Shellcode must run correctly wherever it is placed: it must be position-independent code (PIC).
• Practical rules:
• No hardcoded absolute addresses.
• Use relative addressing and register-relative references.
• Common trick: compute needed data on the stack at runtime rather than referencing a fixed data section.