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

From	Ard Biesheuvel <ard.biesheuvel@linaro.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH v4 3/3] modversions: treat symbol CRCs as 32 bit quantities on 64 bit archs
Date	2017-01-19 10:40 +0100
Message-ID	<t1hmj-8aB-29@gated-at.bofh.it> (permalink)
References	(4 earlier) <t0YWm-4Nd-29@gated-at.bofh.it> <t13jk-7zO-11@gated-at.bofh.it> <t13jk-7zO-9@gated-at.bofh.it> <t17dg-1CE-19@gated-at.bofh.it> <t18Cl-2D0-1@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On 19 January 2017 at 00:15, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> On Wed, Jan 18, 2017 at 2:37 PM, Ard Biesheuvel
> <ard.biesheuvel@linaro.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.
>

This is simply because modpost still uses the value of the symbol
rather than the value it points to to generate the /other/ side of the
comparison (i.e., Module.symvers etc)

I will look into updating modpost to dereference the symbol as well,
and update the RFC patch accordingly.

Thread

[PATCH v4 3/3] modversions: treat symbol CRCs as 32 bit quantities on 64 bit archs Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2017-01-17 20:30 +0100
  Re: [PATCH v4 3/3] modversions: treat symbol CRCs as 32 bit  quantities on 64 bit archs Linus Torvalds <torvalds@linux-foundation.org> - 2017-01-18 00:50 +0100
    Re: [PATCH v4 3/3] modversions: treat symbol CRCs as 32 bit  quantities on 64 bit archs Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2017-01-18 12:40 +0100
      Re: [PATCH v4 3/3] modversions: treat symbol CRCs as 32 bit  quantities on 64 bit archs Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2017-01-18 15:00 +0100
        Re: [PATCH v4 3/3] modversions: treat symbol CRCs as 32 bit  quantities on 64 bit archs Linus Torvalds <torvalds@linux-foundation.org> - 2017-01-18 19:40 +0100
          Re: [PATCH v4 3/3] modversions: treat symbol CRCs as 32 bit  quantities on 64 bit archs Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2017-01-18 23:50 +0100
            Re: [PATCH v4 3/3] modversions: treat symbol CRCs as 32 bit  quantities on 64 bit archs Linus Torvalds <torvalds@linux-foundation.org> - 2017-01-19 01:20 +0100
              Re: [PATCH v4 3/3] modversions: treat symbol CRCs as 32 bit  quantities on 64 bit archs Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2017-01-19 10:40 +0100
                Re: [PATCH v4 3/3] modversions: treat symbol CRCs as 32 bit  quantities on 64 bit archs Linus Torvalds <torvalds@linux-foundation.org> - 2017-01-19 18:30 +0100
                Re: [PATCH v4 3/3] modversions: treat symbol CRCs as 32 bit  quantities on 64 bit archs Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2017-01-20 13:30 +0100
        Re: [PATCH v4 3/3] modversions: treat symbol CRCs as 32 bit  quantities on 64 bit archs Linus Torvalds <torvalds@linux-foundation.org> - 2017-01-18 19:40 +0100
        RE: [PATCH v4 3/3] modversions: treat symbol CRCs as 32 bit  quantities on 64 bit archs David Laight <David.Laight@ACULAB.COM> - 2017-01-19 18:10 +0100

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