linux-kernel - Re: [llvmlinux] percpu | bitmap issue? (Cannot boot on bare metal due to a kernel NULL pointer dereference)

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Message-ID: <CA+icZUXYyxPZH8+a_oaU-Zznshm=peagY3YWEAOSdzKbV2dWzg@mail.gmail.com>
Date:	Mon, 14 Sep 2015 11:55:52 +0200
From:	Sedat Dilek <sedat.dilek@...il.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Peter Zijlstra <peterz@...radead.org>, Baoquan He <bhe@...hat.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Tejun Heo <tj@...nel.org>, Christoph Lameter <cl@...ux.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Thomas Graf <tgraf@...g.ch>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	llvmlinux@...ts.linuxfoundation.org
Subject: Re: [llvmlinux] percpu | bitmap issue? (Cannot boot on bare metal due
 to a kernel NULL pointer dereference)

On Mon, Sep 14, 2015 at 11:35 AM, Ingo Molnar <mingo@...nel.org> wrote:
>
> * Peter Zijlstra <peterz@...radead.org> wrote:
>
>> > I invite you to join the discussion at LLVMLinux... As I know... "YES, you
>> > can." Linux x86/x86_64 (assembler) Kung-Fu. ( I admit I have not these skillz.
>> > )
>>
>> Its a matter of time for me; I simply do not have enough time as it is so I have
>> to make choices.
>
> We are also willing to apply clean, sensible patches.
>
> Alas that collection of llvm patches quoted in this thread:
>
>   30 files changed, 188 insertions(+), 161 deletions(-)
>
> had quite a few objectionable hacks in them.
>

AFAICS LLVMLinux is still a work-in-progress project.

Three patches are labeled with "DO-NOT-UPSTREAM"...

      DO-NOT-UPSTREAM scsi, osd, LLVMLinux: Remove __weak attribute
      WORKAROUND DO-NOT-UPSTREAM x86, boot: Work around clang PR18415.
      DO-NOT-UPSTREAM xen, LLVMLinux: Remove VLAIS from xen mmu

I cannot say much to the other patches - what status they have -
"reported to BTS and have no feedback" or "still discussed" or
whatever.

Some bug-reports are very old - especially in the LLLVM and CLANG BTS.

Can you be concrete on the patches which have in your eyes "a few
objectionable hacks in"?

>From my side... How can the correbolation be improved...?

Linux kernel development <-> LLVMLinux development <-> LLVM/CLANG development

BTW, LLVMLinux is a project hosted at Linux Foundation.

I also remember the interview with Linus and c't magazine (German, I
bought this edition) where he talks about compiler and especially
using LLVM for compiling a Linux-kernel.

If you look at the git-logs, there are people found bugs using
LLVM/CLANG and fixed them.
Personally, I like the "verbose" output of LLVM/CLANG more than GCC v4.9.
I did not try any GCC v5.x.

Thanks.

- Sedat -

[1] http://www.heise.de/ct/ausgabe/2014-25-Linus-Torvalds-im-Interview-2449660.html
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