Re: linux-next: Tree for Oct 18 (objtool)

[Peter Zijlstra]

On Mon, Oct 21, 2019 at 03:19:48PM +0200, Christian Brauner wrote:
> On Mon, Oct 21, 2019 at 03:11:49PM +0200, Peter Zijlstra wrote:

> > By popular request; here's that alternative. Completely untested :-)
> 
> Am I not getting some mails? :)

You're not on the 'right' IRC channels :-)

> I prefer this one as it allows us to avoid working around this in
> usercopy.c. Should especially make if this potentially helps in other
> cases as well?

That was Josh's argument too.

Personally I think GCC is being a moron here, because with value range
analysis it should be able to prove the shift-UB cannot happen (the <
sizeof(unsigned long) conditions on both), but alas, it emits the UBSAN
calls anyway.