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Re: [kernel-hardening] Re: [PATCH v1 0/2] Introduce the initify gcc plugin

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On Tue, 2016-06-28 at 18:07 -0400, Valdis.Kletnieks@vt.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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[PATCH v1 0/2] Introduce the initify gcc plugin Emese Revfy <re.emese@gmail.com> - 2016-06-28 13:30 +0200
  [PATCH v1 2/2] Mark functions with the __nocapture attribute Emese Revfy <re.emese@gmail.com> - 2016-06-28 13:40 +0200
    Re: [PATCH v1 2/2] Mark functions with the __nocapture attribute Joe Perches <joe@perches.com> - 2016-06-28 18:50 +0200
      Re: [PATCH v1 2/2] Mark functions with the __nocapture attribute Emese Revfy <re.emese@gmail.com> - 2016-06-28 22:40 +0200
        Re: [PATCH v1 2/2] Mark functions with the __nocapture attribute Joe Perches <joe@perches.com> - 2016-06-28 23:10 +0200
          Re: [PATCH v1 2/2] Mark functions with the __nocapture attribute Emese Revfy <re.emese@gmail.com> - 2016-06-29 20:50 +0200
            Re: [PATCH v1 2/2] Mark functions with the __nocapture attribute Joe Perches <joe@perches.com> - 2016-06-30 02:20 +0200
              Re: [PATCH v1 2/2] Mark functions with the __nocapture attribute Emese Revfy <re.emese@gmail.com> - 2016-07-01 16:00 +0200
    Re: [PATCH v1 2/2] Mark functions with the __nocapture attribute Rasmus Villemoes <linux@rasmusvillemoes.dk> - 2016-06-28 23:00 +0200
      Re: [PATCH v1 2/2] Mark functions with the __nocapture attribute "PaX Team" <pageexec@freemail.hu> - 2016-06-28 23:50 +0200
        Re: [PATCH v1 2/2] Mark functions with the __nocapture attribute Rasmus Villemoes <linux@rasmusvillemoes.dk> - 2016-06-29 00:50 +0200
      Re: [PATCH v1 2/2] Mark functions with the __nocapture attribute Emese Revfy <re.emese@gmail.com> - 2016-06-29 20:40 +0200
  Re: [PATCH v1 0/2] Introduce the initify gcc plugin Emese Revfy <re.emese@gmail.com> - 2016-06-28 13:40 +0200
  [PATCH v1 1/2] Add the initify gcc plugin Emese Revfy <re.emese@gmail.com> - 2016-06-28 13:40 +0200
    Re: [PATCH v1 1/2] Add the initify gcc plugin Rasmus Villemoes <linux@rasmusvillemoes.dk> - 2016-06-28 23:10 +0200
      Re: [PATCH v1 1/2] Add the initify gcc plugin Kees Cook <keescook@chromium.org> - 2016-06-29 17:00 +0200
      Re: [PATCH v1 1/2] Add the initify gcc plugin Emese Revfy <re.emese@gmail.com> - 2016-06-29 21:10 +0200
  Re: [kernel-hardening] [PATCH v1 0/2] Introduce the initify gcc  plugin Mark Rutland <mark.rutland@arm.com> - 2016-06-28 15:00 +0200
    Re: [kernel-hardening] [PATCH v1 0/2] Introduce the initify gcc  plugin Emese Revfy <re.emese@gmail.com> - 2016-06-28 18:10 +0200
      Re: [kernel-hardening] [PATCH v1 0/2] Introduce the initify gcc plugin Kees Cook <keescook@chromium.org> - 2016-06-28 22:50 +0200
        Re: [kernel-hardening] [PATCH v1 0/2] Introduce the initify gcc  plugin Mark Rutland <mark.rutland@arm.com> - 2016-06-29 10:30 +0200
          Re: [kernel-hardening] [PATCH v1 0/2] Introduce the initify gcc  plugin Mark Rutland <mark.rutland@arm.com> - 2016-06-29 20:00 +0200
            Re: [kernel-hardening] [PATCH v1 0/2] Introduce the initify gcc  plugin Emese Revfy <re.emese@gmail.com> - 2016-06-29 20:30 +0200
  Re: [PATCH v1 0/2] Introduce the initify gcc plugin Joe Perches <joe@perches.com> - 2016-06-28 18:40 +0200
    Re: [PATCH v1 0/2] Introduce the initify gcc plugin Joe Perches <joe@perches.com> - 2016-06-28 20:50 +0200
      Re: [PATCH v1 0/2] Introduce the initify gcc plugin Rasmus Villemoes <linux@rasmusvillemoes.dk> - 2016-06-28 21:10 +0200
        Re: [PATCH v1 0/2] Introduce the initify gcc plugin Emese Revfy <re.emese@gmail.com> - 2016-06-28 22:30 +0200
  Re: [PATCH v1 0/2] Introduce the initify gcc plugin Mathias Krause <minipli@ld-linux.so> - 2016-06-28 19:10 +0200
    Re: [PATCH v1 0/2] Introduce the initify gcc plugin Emese Revfy <re.emese@gmail.com> - 2016-06-28 22:30 +0200
  Re: [PATCH v1 0/2] Introduce the initify gcc plugin Joe Perches <joe@perches.com> - 2016-06-29 00:00 +0200
    Re: [kernel-hardening] Re: [PATCH v1 0/2] Introduce the initify gcc plugin Valdis.Kletnieks@vt.edu - 2016-06-29 00:10 +0200
      Re: [kernel-hardening] Re: [PATCH v1 0/2] Introduce the initify gcc  plugin Joe Perches <joe@perches.com> - 2016-06-29 02:00 +0200

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