linux-kernel - Re: [PATCH v4 3/3] modversions: treat symbol CRCs as 32 bit quantities on 64 bit archs

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Message-ID: <CA+55aFzpCdSAP1ef9d+8SWByEa5ekP0V2T6feKPMZq_cOfiOUA@mail.gmail.com>
Date:   Wed, 18 Jan 2017 16:15:14 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Jessica Yu <jeyu@...hat.com>,
        Rusty Russell <rusty@...tcorp.com.au>,
        "Suzuki K. Poulose" <suzuki.poulose@....com>,
        Will Deacon <will.deacon@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Arnd Bergmann <arnd@...db.de>,
        Al Viro <viro@...iv.linux.org.uk>,
        ppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH v4 3/3] modversions: treat symbol CRCs as 32 bit
 quantities on 64 bit archs

On Wed, Jan 18, 2017 at 2:37 PM, Ard Biesheuvel
<ard.biesheuvel@...aro.org> wrote:
>
> For a ballpark number of 10,000 CRCs in the core kernel, this would
> increase the size of the image by 40 KB for 32-bit architectures (and
> if saving 40 KB is essential, chances are you won't be using
> modversions in the first place).

As you say, I don't think the space issue is much of a problem.

I'm more worried about the replacement of one crazy model that has
problems due to linker subtlety with _another_ one.

Your genksyms.c change is not exactly obvious. I looked at it, and my
brain just shut down. Why both the

  LONG(0x%08lx);

_and_ the

  "%s__crc_%s = 0x%08lx;\n"

in the linker script? I'm sure there's a good reason, but I'd like to
see a more explicit explanation fo what the generated linker script
does and what the rules are.

         Linus