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

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Message-ID: <CA+icZUUq86Pr1jW9CLcsebC4otR8Y96dogoEi=ttZuAyx4=vjw@mail.gmail.com>
Date:	Mon, 7 Sep 2015 22:31:01 +0200
From:	Sedat Dilek <sedat.dilek@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Use (two) different compilers at build-time?

On Mon, Sep 7, 2015 at 10:15 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> On Mon, Sep 7, 2015 at 12:12 PM, Sedat Dilek <sedat.dilek@...il.com> wrote:
>>
>> is it possible to use a different compiler at build-time?
>>
>> I have here a problem with mm/percpu.c and wanted to build everything
>> with LLVM/Clang but this single file with GCC.
>>
>> Is that possible?
>
> It should work fine. It's occasionally how people bisect compiler bugs
> in the kernel (although then it's usually just two different versions
> of the same compiler), and I think people have done that with llvm
> too. After all, llvm object files link to gcc-produced object files in
> user space (ie libraries are most often compiled with different
> compilers).
>
> So no _guarantees_ (especially since the kernel sometimes does odd
> things), but there's no overwhelming reason it shouldn't work, and
> there are several reasons it should be fine.
>

OK.

So, how do I do that conveniently?

In case of percpu.o - hack in the mm/Makefile?

So, I have a percpu.o compiled with clang in my build-dir and want to
recompile just that single file with gcc and create a new bzImage.

Hope I could explain it more exactly.

- Sedat -
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