Re: Cleanup for cryptographic algorithms vs. compiler optimizations

On Fri, 11.06.2010 at 21:37:29 +0200, Dag-Erling Smørgrav wrote:
Ulrich Spörlein <uqs@xxxxxxxxxxxxx> writes:
optimizing compilers have a tendency to remove assignments that have
no side effects. The code in sys/crypto/sha2/sha2.c is doing a lot of
zeroing variables, which is however optimized away. [...] Is there a
canonical way to zero those variables and should we use them (memset
perhaps? what are the performance implications?)

If you stick these variables in a struct, you can memset the struct to
zero them; if there are many of them, it may be faster than zeroing them
individually.

Alternatively, you can use something like this:

#define FORCE_ASSIGN(type, var, value) \
*(volatile type *)&(var) = (value)

Interesting trick, thanks. I'll try this ...

Uli
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