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Message-ID: <1467158049.24287.90.camel@perches.com>
Date: Tue, 28 Jun 2016 16:54:09 -0700
From: Joe Perches <joe@...ches.com>
To: Valdis.Kletnieks@...edu, kernel-hardening@...ts.openwall.com
Cc: Emese Revfy <re.emese@...il.com>, Matt Davis <mattdavis9@...il.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,
linux@...musvillemoes.dk, david.brown@...aro.org,
benh@...nel.crashing.org, tglx@...utronix.de, akpm@...ux-foundation.org,
jlayton@...chiereds.net, arnd@...db.de
Subject: Re: Re: [PATCH v1 0/2] Introduce the initify gcc
plugin
On Tue, 2016-06-28 at 18:07 -0400, Valdis.Kletnieks@...edu wrote:
> On Tue, 28 Jun 2016 14:49:15 -0700, Joe Perches said:
>
> >
> > Another potentially useful plugin, especially for embedded systems,
> > would be to compress any string literal marked with
> >
> > __attribute__((format(printf, string-index,)))
> >
> > and decompress the compressed format on the stack in lib/vsprintf.c
> > vsnprintf just before use.
> Are there enough such strings in the kernel to make it worth the effort?
> I'm assuming that the string literals in printk("some string here") are
> automatically so marked?
Yes, that's the concept.
> Is there a minimum length under which the compression overhead actually
> makes it larger?
No, compression would have to be possible, otherwise it'd
be stored directly. Compression would use a special
"compressed string" header with a 2 byte overhead and
then stored with no trailing \0.
Something like struct compressed_format_header {
u8 flag; /* Must be ASCII STX or "\b" */
u8 length;
}
Depends on the config of course, but it could reduce total
image size ~50k on an x86-32 defconfig
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