Re: [Question] Alignment requirement for readX() and writeX()

Boqun Feng
2021-07-31T01:51:39Z

On Fri, Jul 30, 2021 at 10:24:53PM +0200, Arnd Bergmann wrote:
> On Fri, Jul 30, 2021 at 7:31 PM Boqun Feng <boqun.feng@gmail.com> wrote:
> > On Fri, Jul 30, 2021 at 06:58:30PM +0200, Arnd Bergmann wrote:
> >
> > If we want to check, I'd expect we do the checks inside
> > readX()/writeX(), for example, readl() could be implemented as:
> >
> > #define readl(c) \
> > ({ \
> > u32 __v; \
> > \
> > /* alignment checking */ \
> > BUG_ON(c & (sizeof(__v) - 1)); \
> > __v = readl_relaxed(c); \
> > __iormb(__v); \
> > __v; \
> > })
> >
> > It's a runtime check, so if anyone hates it I can understand ;-)
>
> Right, I really don't think that adds any value, this just replaces one
> oops message with a more different oops message, while adding
> some overhead.
>

Agreed. I wasn't planning to propose this kind of checks for C code.
Just want to understand better on the alignment requirement of these
APIs. Thanks ;-)

Regards,
Boqun

> Arnd