Date: Mon, 14 Jun 2010 19:38:15 +0200 From: Tijl Coosemans <tijl@coosemans.org> To: freebsd-current@freebsd.org Subject: Re: Cleanup for cryptographic algorithms vs. compiler optimizations Message-ID: <201006141938.15200.tijl@coosemans.org> In-Reply-To: <86y6els1bm.fsf@ds4.des.no> References: <20100611162118.GR39829@acme.spoerlein.net> <201006112304.10952.tijl@coosemans.org> <86y6els1bm.fsf@ds4.des.no>
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On Friday 11 June 2010 23:31:57 Dag-Erling Sm=C3=B8rgrav wrote:
> Tijl Coosemans <tijl@coosemans.org> writes:
>> Dag-Erling Sm=C3=B8rgrav <des@des.no> writes:
>>> #define FORCE_ASSIGN(type, var, value) \
>>> *(volatile type *)&(var) =3D (value)
>> memset can be optimised away as well. The only way is to declare
>> those variables volatile.
>=20
> Assigning through a volatile pointer, as in FORCE_ASSIGN(), also
> works, even if the variable itself is not volatile.
Just thought of problem with this macro when var is a pointer. Then
volatile applies to the referenced memory and not the variable. So
you should move the volatile keyword, like so:
#define FORCE_ASSIGN(type, var, value) \
*(type volatile *)&(var) =3D (value)
And if you can use GNU extensions this can be simplified to:
#define FORCE_ASSIGN(var, value) \
*(typeof(var) volatile *)&(var) =3D (value)
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