Re: [PATCH] uapi/asm/termbits: Use the U integer suffix for bit fields

[Greg KH <gregkh@linuxfoundation.org>]

On Wed, Jun 12, 2024 at 04:00:18PM +0200, Alejandro Colomar wrote:
> Hi Greg,
> 
> On Wed, Jun 12, 2024 at 03:35:20PM GMT, Greg KH wrote:
> > On Wed, Jun 12, 2024 at 03:16:58PM +0200, Alejandro Colomar wrote:
> > > Constants that are to be used in bitwise operations should be unsigned,
> > > or a user could easily trigger Undefined Behavior.
> > 
> > Wait, do we really have such broken compilers out there?
> 
> I meant this as a generic statement that signed integers on bitwise ops
> are bad, not as a specific statement that these values would trigger UB.
> 
> I expect that these specific values and the operations done on them
> probably don't trigger UB, since the shifts are done by a controlled
> amount, and there are justa few operations done on them.

These, for the most part, are NOT used as shifts.

> For example, a left shift where a set bit overflows the type (e.g.,
> 1<<32), causes UB.

Sure, but that's not in play here.

> The reason why it's better to avoid this at all even if we know these
> values work fine, is that programs using <asm/termbits.h> would need to
> disable those compiler warnings, which could silence warnings on other
> code which might be broken.

But again, you aren't using these as bit shifts, they are bit masks, or
values, only.

> TL;DR: The kernel isn't broken, but improving this would allow users to
> enable stricter warnings, which is a good thing.

Enable it where?

thanks,

greg k-h