Re: [PATCH] sha: prevent removal of memset as dead store in sha1_update()

Mikael Pettersson
2010-02-25T17:09:43Z

Brian Gerst wrote:
> Would barrier() (which is a simple memory clobber) after the memset work?

I don't know. It's implemented as an asm with a "memory" clobber,
but I wouldn't bet on that forcing previous writes to a dying object
to actally be performed (it would have to have a data-dependency on
the dying object, but I don't think there is one).

void secure_bzero(void *p, size_t n)
{
memset(p, 0, n);
asm("" : : "m"(*(char*)p));
}

seems to work, but as the object in general will be larger than a
single byte, I'd like to see some confirmation from the gcc folks
first that this will in fact work.