Examine and change blocked signals
long sys_sigprocmask(int how, old_sigset_t __user * nset, old_sigset_t __user * oset);
how
whether to add, remove, or set signals
nset
signals to add or remove (if non-null)
oset
previous value of signal mask if non-null
Some platforms have their own version with special arguments; others support only sys_rt_sigprocmask.