RE: [PATCH] crypto: caam - Avoid GCC memset bug warning

[David Laight <David.Laight@ACULAB.COM>]

From: Herbert Xu
> Sent: 29 December 2022 01:49
> 
> On Wed, Dec 28, 2022 at 12:30:35PM +0100, Uwe Kleine-König wrote:
> >
> > > -	if (len) /* avoid sparse warning: memcpy with byte count of 0 */
> > > +	/* Avoid gcc warning: memcpy with data == NULL */
> > > +	if (!IS_ENABLED(CONFIG_CRYPTO_DEV_FSL_CAAM_DEBUG) || data)
> >
> > I just tried: For me a plain
> >
> > 	if (data)
> >
> > is also enough to make both gcc and sparse happy.
> 
> Of course it is.  The point of the extra condition is to remove
> the unnecessary check on data unless we are in debugging mode
> (as it is only needed in debugging mode to work around the buggy
> compiler).

IIRC the 'problematic' case is one where 'len' and 'data'
are actually compile-time zeros - in which case you don't
want to call memcpy() at all.
In all other cases I think there is something to copy so you
don't really want the check (or the one in memcpy() will do).

Whether (builtin_constant_p(data) && !data) is good enough is
another matter.
It might need the (sizeof *(1 ? (void *)(data) : (int *)0) == 1)
test.

	David

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