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From: Rasmus Villemoes <linux@rasmusvillemoes.dk>
To: Jessica Yu <jeyu@kernel.org>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>,
	Matthias Maennich <maennich@google.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Joel Fernandes <joel@joelfernandes.org>,
	Martijn Coenen <maco@android.com>,
	Will Deacon <will.deacon@arm.com>, Will Deacon <will@kernel.org>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 4/7] module: avoid code duplication in include/linux/export.h
Date: Tue, 29 Oct 2019 22:11:45 +0100	[thread overview]
Message-ID: <a2e6bdc2-3d35-a3dc-13ef-1ce32f77ef17@rasmusvillemoes.dk> (raw)
In-Reply-To: <20191029191925.GA19316@linux-8ccs>

On 29/10/2019 20.19, Jessica Yu wrote:
> +++ Rasmus Villemoes [27/09/19 13:07 +0200]:
>> On 27/09/2019 11.36, Masahiro Yamada wrote:
>>>
>>> A typical kernel configuration has 10K exported symbols, so it
>>> increases 10KB in rough estimation.
>>>
>>> I did not come up with a good idea to refactor it without increasing
>>> the code size.
>>
>> Can't we put the "aMS" flags on the __ksymtab_strings section? That
>> would make the empty strings free, and would also deduplicate the
>> USB_STORAGE string. And while almost per definition we don't have exact
>> duplicates among the names of exported symbols, we might have both a foo
>> and __foo, so that could save even more.
>>
>> I don't know if we have it already, but we'd need each arch to tell us
>> what symbol to use for @ in @progbits (e.g. % for arm). It seems most
>> are fine with @, so maybe a generic version could be
>>
>> #ifndef ARCH_SECTION_TYPE_CHAR
>> #define ARCH_SECTION_TYPE_CHAR "@"
>> #endif
>>
>> and then it would be
>> section("__ksymtab_strings,\"aMS\","ARCH_SECTION_TYPE_CHAR"progbits,1")
> 
> FWIW, I've just tinkered with this, and unfortunately the strings
> don't get deduplicated for kernel modules :-(
> 
> 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/> :)

> 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.

Rasmus



  reply	other threads:[~2019-10-29 21:11 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-27  9:35 [PATCH 0/7] module: various bug-fixes and clean-ups for module namespace Masahiro Yamada
2019-09-27  9:35 ` [PATCH 1/7] modpost: fix broken sym->namespace for external module builds Masahiro Yamada
2019-09-27  9:56   ` Masahiro Yamada
2019-09-27 11:46   ` Matthias Maennich
2019-09-27  9:35 ` [PATCH 2/7] module: swap the order of symbol.namespace Masahiro Yamada
2019-09-27 12:07   ` Matthias Maennich
2019-09-27  9:35 ` [PATCH 3/7] module: rename __kstrtab_ns_* to __kstrtabns_* to avoid symbol conflict Masahiro Yamada
2019-09-27 12:14   ` Matthias Maennich
2019-09-27  9:36 ` [PATCH 4/7] module: avoid code duplication in include/linux/export.h Masahiro Yamada
2019-09-27  9:58   ` Masahiro Yamada
2019-09-27 11:07   ` Rasmus Villemoes
2019-09-27 12:36     ` Matthias Maennich
2019-10-29 19:19     ` Jessica Yu
2019-10-29 21:11       ` Rasmus Villemoes [this message]
2019-10-31 10:13         ` Jessica Yu
2019-10-31 11:03           ` Rasmus Villemoes
2019-10-31 11:26             ` Jessica Yu
2019-09-27  9:36 ` [PATCH 5/7] kbuild: fix build error of 'make nsdeps' in clean tree Masahiro Yamada
2019-09-27 12:44   ` Matthias Maennich
2019-09-27  9:36 ` [PATCH 6/7] nsdeps: fix hashbang of scripts/nsdeps Masahiro Yamada
2019-09-27 13:10   ` Matthias Maennich
2019-09-27  9:36 ` [PATCH 7/7] nsdeps: make generated patches independent of locale Masahiro Yamada
2019-09-27 13:27   ` Matthias Maennich
2019-09-27 15:42     ` Masahiro Yamada
2019-09-27 18:14       ` Greg Kroah-Hartman
2019-09-29  1:18         ` Masahiro Yamada
2019-09-29  1:30           ` Masahiro Yamada
2019-10-01 11:46             ` Matthias Maennich
2019-09-29 10:14           ` Greg Kroah-Hartman
2019-09-27 13:41 ` [PATCH 0/7] module: various bug-fixes and clean-ups for module namespace Matthias Maennich
2019-09-27 15:43   ` Masahiro Yamada
2019-10-02 18:57   ` Jessica Yu
2019-10-02 20:43     ` Matthias Maennich
2019-10-03  1:26     ` Masahiro Yamada
2019-10-03  8:03     ` Masahiro Yamada

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