Re: [GIT PULL] x86/build changes for v4.17

[Josh Poimboeuf]

On Wed, Apr 04, 2018 at 04:53:52PM +0000, Nick Desaulniers wrote:
> (re-sending as plain text)
> 
> On Wed, Apr 4, 2018 at 2:38 AM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
> > There are known-bugs with building a kernel with clang right now (I
> > pointed one out a few days ago about NULL checks being deleted from the
> > clang output for no good reason, which really is scary for obvious
> > reasons).
> 
> Is this the thread you are referring to?
> https://lkml.org/lkml/2018/3/27/1286
> 
> It's definitely something curious that I'll need to sit down and
> investigate more.  If there are other known instances, it would be good to
> let me know.

As Matthias mentioned elsewhere, it sounds like they're planning to
implement -fno-delete-null-pointer-checks, which would presumably fix
the above issue.

Aside from the above-mentioned debugfs NULL checks, there was also
another (seemingly valid) objtool warning:

  arch/x86/mm/pti.o: warning: objtool: pti_init() falls through to next function pti_user_pagetable_walk_pmd()

I don't know if that one was also caused by removed NULL checks, but
it's worth investigating.

More details (and the .o file) here:

  https://lkml.kernel.org/r/20180319232255.GF37438@xxxxxxxxxx

-- 
Josh