possible issue of sigcontext alignment on user stack

Hi, guys.

I think there is a possible structure alignment issue around
sigcontext store built on user stack

In sendsig()::sig_machdep.c, the pointer value "struct
sigcontext *scp"  made from cast is wind up "scp--" to
have sigcontext structure storage.  Then, structure alignment
would matter in the case of 64bit register_t.

    scp--;

I guess the above should be like as;

    scp = (struct sigcontext *)(((unsigned long)(scp - 1)) &~ ALIGNBYTES);

Your thoughts?  Donno what the most sane cast should be for LP64 case.

Toru Nishimura/ALKYL Technology