linux-kernel - Re: [PATCH v1 1/2] Add the initify gcc plugin

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Date:	Tue, 28 Jun 2016 23:05:56 +0200
From:	Rasmus Villemoes <linux@...musvillemoes.dk>
To:	Emese Revfy <re.emese@...il.com>
Cc:	kernel-hardening@...ts.openwall.com, pageexec@...email.hu,
	spender@...ecurity.net, mmarek@...e.com, keescook@...omium.org,
	linux-kernel@...r.kernel.org, yamada.masahiro@...ionext.com,
	linux-kbuild@...r.kernel.org, minipli@...linux.so,
	linux@...linux.org.uk, catalin.marinas@....com,
	david.brown@...aro.org, benh@...nel.crashing.org,
	tglx@...utronix.de, akpm@...ux-foundation.org,
	jlayton@...chiereds.net, arnd@...db.de
Subject: Re: [PATCH v1 1/2] Add the initify gcc plugin

On Tue, Jun 28 2016, Emese Revfy <re.emese@...il.com> wrote:

> The kernel already has a mechanism to free up code and data memory that
> is only used during kernel or module initialization.
> This plugin will teach the compiler to find more such code and data that
> can be freed after initialization.
> It has two passes. The first one tries to find all functions that
> can be become __init/__exit. The second one moves string constants
> (local variables and function string arguments marked by
> the nocapture attribute) only referenced in __init/__exit functions
> to the __initconst/__exitconst sections.
> It reduces memory usage. This plugin can be useful for embedded systems.

May I suggest, as a followup patch, a debug option/plugin parameter to
put the strings in a section which will not be reaped after init, but
just marked inaccessible, with graceful handling of bad accesses (print
a big fat warning, make the page(s) readable, continue)?

Rasmus