linux-kernel - Re: Use (two) different compilers at build-time?

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Message-ID: <CA+icZUVhqpCDXB_zswRiQ4zviNKh=Zb6Yw2jJUts89XkMtV=8A@mail.gmail.com>
Date:	Sun, 13 Sep 2015 17:21:41 +0200
From:	Sedat Dilek <sedat.dilek@...il.com>
To:	Fengguang Wu <fengguang.wu@...el.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Use (two) different compilers at build-time?

On Thu, Sep 10, 2015 at 2:25 AM, Fengguang Wu <fengguang.wu@...el.com> wrote:
> On Mon, Sep 07, 2015 at 09:12:58PM +0200, Sedat Dilek wrote:
>> Hi,
>>
>> is it possible to use a different compiler at build-time?
>
> btw, it'd be great if clang can just work on mainline kernel.
>

I am not a member of that LLVMLinux team, but they upstreamed a lot of patches.

> I tried to run clang in 0day kbuild tests, however make aborts
> quickly in seconds. There are dozens of clang patches provided in
>
>     http://llvm.linuxfoundation.org/index.php/Main_Page
>
> however such our-of-tree patches are not bisect friendly.
>

I agree, there is a high potential for improvements in LLVMLinux :-).

Unfortunately, I struggled here some days with $COMPILER's
inline-optimization (disable | force| noinline) and it turned out to
be a "known" x86-hweight issue (a patch was archived and thrown away
from the series of x86 patches).

Finally, I have a "buildable" and "running-on-bare-metal"
llvmlinux-patched Linux v4.2 here on Ubuntu/precise AMD64.

It is everytime interesting to see where the root cause sits.
It's like in everyday life - never assume - just ask - stay curious
and attentive :-).

- Sedat -

[1] http://lists.linuxfoundation.org/pipermail/llvmlinux/2015-September/001357.html
[2] http://lists.linuxfoundation.org/pipermail/llvmlinux/2015-September/001358.html
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