RE: AW: [PATCH] soc: aspeed: fix a ternary sign expansion bug

David Laight
2021-04-23T14:55:38Z

From: Sergey Organov
> Sent: 23 April 2021 15:40
>
> Walter Harms <wharms@bfs.de> writes:
>
> > as indepentent observer,
> > i would go for Dans solution:
> >
> > ret = kfifo_to_user();
> > /* if an error occurs just return */
> > if (ret)
> > return ret;
> >
> > /* otherwise return the copied number of bytes */
> >
> > return copied;
> >
> > there is no need for any deeper language knowledge,
>
> Yep, but this is not idiomatic C, so one looking at this code would
> tend to convert it back to ternary, and the actual problem here is that
> the type of 'copied' does not match the return type of the function.

Actually changing the type of 'ret' to ssize_t is probably
the safest change.

That works until someone tries to optimise out 'ret' by doing:

return kfifo_to_user(...) ?: count;

Or rattle through and remove the 'pass by reference' 'count'
parameter from kfifo_to_user() in favour of returning the
value the callers want.

I need to stop looking at this code :-)

David

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