[Cryptography] Making sure memory erasure is not optimized away

[Salz, Rich]

>    I don't see how you're going to do any better than using qualifiers
    like "volatile" in C and C#.

OpenSSL we had to drop into assembler in places where we could.  Look up `OPENSSL_cleanse`  The C function had to use an indirect call to prevent it being optimized away:
	typedef void *(*memset_t)(void *, int, size_t);
	static volatile memset_t memset_func = memset;

	void OPENSSL_cleanse(void *ptr, size_t len)
	{
	    memset_func(ptr, 0, len);
	}       

>    PS: Every operating system I know zeros storage before adding it to
    a process, so I'm kind of wondering what the threat model is here.

Bugs within a program may allow an adversary to read memory that the program was expecting to be cleared.