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From: Rasmus Villemoes <linux@rasmusvillemoes.dk>
To: Masahiro Yamada <yamada.masahiro@socionext.com>,
	Jessica Yu <jeyu@kernel.org>
Cc: 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: Fri, 27 Sep 2019 13:07:33 +0200
Message-ID: <f2e28d6b-77c5-5fe2-0bc4-b24955de9954@rasmusvillemoes.dk> (raw)
In-Reply-To: <20190927093603.9140-5-yamada.masahiro@socionext.com>

On 27/09/2019 11.36, Masahiro Yamada wrote:
> include/linux/export.h has lots of code duplication between
> EXPORT_SYMBOL and EXPORT_SYMBOL_NS.
> 
> To improve the maintainability and readability, unify the
> implementation.
> 
> When the symbol has no namespace, pass the empty string "" to
> the 'ns' parameter.
> 
> The drawback of this change is, it grows the code size.
> When the symbol has no namespace, sym->namespace was previously
> NULL, but it is now am empty string "". So, it increases 1 byte
> for every no namespace EXPORT_SYMBOL.
> 
> 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")

But I don't know if any tooling relies on the strings not being
deduplicated.

Rasmus

  parent reply index

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 [this message]
2019-09-27 12:36     ` Matthias Maennich
2019-10-29 19:19     ` Jessica Yu
2019-10-29 21:11       ` Rasmus Villemoes
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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