Re: x86 - clang / objtool status

[Josh Poimboeuf]

On Wed, Jul 24, 2019 at 09:47:32AM +0200, Peter Zijlstra wrote:
> On Tue, Jul 23, 2019 at 09:43:24PM -0500, Josh Poimboeuf wrote:
> > On Thu, Jul 18, 2019 at 10:40:09PM +0200, Thomas Gleixner wrote:
> > 
> > >   drivers/gpu/drm/i915/gem/i915_gem_execbuffer.o: warning: objtool: .altinstr_replacement+0x86: redundant UACCESS disable
> > 
> > Looking at this one, I think I agree with objtool.
> > 
> > PeterZ, Linus, I know y'all discussed this code a few months ago.
> > 
> > __copy_from_user() already does a CLAC in its error path.  So isn't the
> > user_access_end() redundant for the __copy_from_user() error path?
> 
> Hmm, is this a result of your c705cecc8431 ("objtool: Track original function across branches") ?
> 
> I'm thinking it might've 'overlooked' the CLAC in the error path before
> (because it didn't have a related function) and now it sees it and
> worries about it.
> 
> Then again, I'm not seeing this warning on my GCC builds; so what's
> happening?

According to the github issue[1] my patch doesn't fix the warning with
Clang.  So questions remain:

a) what is objtool actually warning about?

b) why doesn't objtool detect the case I found?


I can look at it later, post-meetings.


[1] https://github.com/ClangBuiltLinux/linux/issues/617

-- 
Josh