linux-kernel - Re: [PATCH 4/7] module: avoid code duplication in include/linux/export.h

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Message-ID: <20191031112602.GD2177@linux-8ccs>
Date:   Thu, 31 Oct 2019 12:26:03 +0100
From:   Jessica Yu <jeyu@...nel.org>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Matthias Maennich <maennich@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Martijn Coenen <maco@...roid.com>,
        Will Deacon <will.deacon@....com>,
        Will Deacon <will@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/7] module: avoid code duplication in
 include/linux/export.h

+++ Rasmus Villemoes [31/10/19 12:03 +0100]:
>On 31/10/2019 11.13, Jessica Yu wrote:
>> +++ Rasmus Villemoes [29/10/19 22:11 +0100]:
>>> On 29/10/2019 20.19, Jessica Yu wrote:
>
>>>> Apparently ld does not do the deduplication for SHF_MERGE|SHF_STRINGS
>>>> sections for relocatable files (ld -r), which kernel modules are. See:
>>>>
>>>>    https://sourceware.org/ml/binutils/2009-07/msg00291.html
>>>
>>> I know <https://patches-gcc.linaro.org/patch/5858/> :)
>>
>> That is exactly what we need! :)
>>
>>>> But, the strings do get deduplicated for vmlinux. Not sure if we can
>>>> find a workaround for modules or if the benefit is significant enough
>>>> if it only for vmlinux.
>>>
>>> I think it's definitely worth if, even if it "only" benefits vmlinux for
>>> now. And I still hope to revisit the --force-section-merge some day, but
>>> it's very far down my priority list.
>>
>> Yeah, I think it's worth having too.
>>
>> If you don't have any extra cycles at the moment, and it's far down
>> your priority list, do you mind if I take a look and maybe try to push
>> that patch of yours upstream again?
>
>Knock yourself out :) IIRC, it did actually work for the powerpc I was
>targeting, but I don't remember if that was just "readelf/objdump
>inspection of the ELF files looks reasonable" or if I actually tried
>loading the modules. I've pushed the patch to
>https://github.com/Villemoes/binutils-gdb/commit/107b9302858fc5fc1a1690f4a36e1f80808ab421
>so you don't have to copy-paste from a browser.

Thanks a bunch!

>I don't know how successful I'd
>> be, but now since it's especially relevant for namespaces, it's
>> definitely worth looking at again.
>
>Yeah, but even ignoring namespaces, it would be nice to have format
>strings etc. deduplicated. Please keep me cc'ed on any progress you make.

Thanks, I'll keep you posted if I manage to get somewhere with it :)