The Red Zone

• System V reserves a 128-byte red zone just below RSP ([rsp-128] .. [rsp-1]).
• Leaf functions (that call nothing) may use it for scratch data without adjusting RSP.
• Signal handlers and interrupts must not clobber it.
• Relevance: affects exact offsets when crafting stack payloads for small/leaf functions; do not assume everything above RSP is untouched.