• sig_overwrite_sp.c Overwrite ss_sp, ss_size directly from sigframe during signal handler from userspace.

Below demo how sigaltstack can be nested, hence why restore_altstack is needed inside rt_sigreturn.

• sigaltstack_from_sighandler.c Call sigaltstack inside signal handler
• sigaltstack_twice_from_sighandler.c Calling sigaltstack inside signal hanlder and where altstack is in use by the sighandler. Note: in order for this to be successful, the altstack must be created with SS_AUTODISARM.