linux-kernel - Re: [PATCH, RFC] byteorder: sanity check toolchain vs kernel endianess

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Date:   Wed, 15 May 2019 08:53:02 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Christoph Hellwig <hch@....de>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nick Kossifidis <mick@....forth.gr>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Andrew Donnellan <andrew.donnellan@....ibm.com>
Subject: Re: [PATCH, RFC] byteorder: sanity check toolchain vs kernel endianess

On Mon, May 13, 2019 at 2:04 PM Christoph Hellwig <hch@....de> wrote:
>
> On Mon, May 13, 2019 at 01:50:19PM +0200, Dmitry Vyukov wrote:
> > > We did have some bugs in the past (~1-2 y/ago) but AFAIK they are all
> > > fixed now. These days I build most of my kernels with a bi-endian 64-bit
> > > toolchain, and switching endian without running `make clean` also works.
> >
> > For the record, yes, it turn out to be a problem in our code (a latent
> > bug). We actually used host (x86) gcc to build as-if ppc code that can
> > run on the host, so it defined neither LE no BE macros. It just
> > happened to work in the past :)
>
> So Nick was right and these checks actually are useful..

Yes, definitely. I wonder if we should also bring back the word size check
from include/asm-generic/bitsperlong.h, which was disabled right
after I originally added that.

      Arnd