Re: [Ksummit-discuss] [CORE TOPIC] [TECH TOPIC] Support (or move towards to) LLVM

[David Woodhouse <dwmw2@infradead.org>]

[-- Attachment #1: Type: text/plain, Size: 2663 bytes --]

On Thu, 2016-07-21 at 07:41 -0600, Shuah Khan wrote:
> On Thu, Jul 21, 2016 at 3:54 AM, David Woodhouse <dwmw2@infradead.org> wrote:
> > On Wed, 2016-07-20 at 19:04 +0200, Jiri Kosina wrote:
> > > On Wed, 20 Jul 2016, Mark Brown wrote:
> > > 
> > > > > > There's a push from certain quarters to move away from GCC to LLVM.
> > > > 
> > > > > This might actually be an interesting topic per se.
> > > > 
> > > > Yes, indeed.
> > > 
> > > Let's make this a real proposal then ... (subject changed). I am again a
> > > bit unsure about the core / tech division here.
> > > 
> > > People who should be invited: proponents of the push from the certain
> > > quarters mentioned by Mark above, and ideally some LLVM folks as well.
> > > 
> > > I've never actually used llvm to compile the kernel (which makes me rather
> > > poor contributor should any such discussion happen), but I've been on the
> > > "receiving side", debugging a crash that turned out to be llvm messing up
> > > with IF in a way that interfers with local_irq_save(), and also suffered
> > > from the followup frustration when I found out that this has been reported
> > > to llvm folks ages ago, and they haven't bothered to fix it (it's now at
> > > least worked around, in a very sub-optimal way (lahf/sahf)).
> > 
> > I got involved in building the kernel with LLVM a little while ago,
> > after accidentally implementing .code16 support in LLVM — for other
> > reasons, but it allowed the arch/x86/boot/ bits to be built with LLVM.
> > 
> > Apart from resolutely not wanting to implement variable length arrays
> > on the stack, the LLVM folks actually seem quite keen to make things
> > work. I'm interested in the problem you report above.. and note the
> > absence of a bug number. Can you provide it?
> > 
> > You're right that it does take a while to get some things fixed, but
> > people *are* doing a fairly good job of identifying them, filing bugs,
> > and implementing workarounds until the bugs can be fixed.
> > 
> > Building with LLVM has also helped to find some real kernel bugs. I'd
> > be keen to get this working more widely.
> > 
> 
> Would you be willing to share your experiences and the nature of bugs
> you were able to find using LLVM. Maybe that could be folded into this
> discussion as a real life experience.

http://llvm.linuxfoundation.org/index.php/Bugs

Probably horrifically out of date. Behan is the best person to ask for
a current status, I suspect...

-- 
David Woodhouse                            Open Source Technology Centre
David.Woodhouse@intel.com                              Intel Corporation

[-- Attachment #2: smime.p7s --]
[-- Type: application/x-pkcs7-signature, Size: 5760 bytes --]