linux-kernel - Re: [PATCH 3/8] x86/boot/64: Add support of additional page table level during early boot

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Date:   Tue, 11 Apr 2017 13:28:45 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Andi Kleen <ak@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Andy Lutomirski <luto@...capital.net>,
        linux-arch@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/8] x86/boot/64: Add support of additional page table
 level during early boot


* Kirill A. Shutemov <kirill@...temov.name> wrote:

> On Tue, Apr 11, 2017 at 09:02:03AM +0200, Ingo Molnar wrote:
> > I realize that you had difficulties converting this to C, but it's not going to 
> > get any easier in the future either, with one more paging mode/level added!
> > 
> > If you are stuck on where it breaks I'd suggest doing it gradually: first add a 
> > trivial .c, build and link it in and call it separately. Then once that works, 
> > move functionality from asm to C step by step and test it at every step.
> 
> I've described the specific issue with converting this code to C in cover
> letter: how to make compiler to generate 32-bit code for a specific
> function or translation unit, without breaking linking afterwards (-m32
> break it).

Have you tried putting it into a separate .c file, and building it 32-bit?

I think arch/x86/entry/vdso/Makefile contains an example of how to build 32-bit 
code even on 64-bit kernels.

Thanks,

	Ingo