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:

quoted

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.

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

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.

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

With this change, can the glibc versions then be dropped to just rely on
these instead?

I don't know.  glibc is CCd, so they can answer that.

Have a lovely day!
Alex

-- 
<https://www.alejandro-colomar.es/>