From: Dave Hansen <dave.hansen@linux.intel.com>
Date: Fri, 12 Dec 2014 18:38:35 +0000 (-0800)
Subject: x86, mpx: Update documentation
X-Git-Tag: omap-for-v3.19/fixes-rc1~26^2~1
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=010e593b140decdc16bb0c1c754b07b1fccb6999;p=pandora-kernel.git

x86, mpx: Update documentation

I was writing some MPX test programs and realized that the
current design makes it tricky.  I did something like:

	bndcfgu |= bnd_dir | BNDCFGU_ENABLE;
	xrstor();
	printf("xrstor done");
	// #BR bounds exception here
	prctl(MPX_ENABLE_MANAGEMENT);

and then compiled the app with "-fcheck-pointer-bounds -mmpx"
to enable MPX instrumentation.

The problem is that there is MPX instrumentation inserted in
to the area of the printf().  The kernel gets a bounds exception
and since management isn't yet enabled, it SIGSEGV's.

Add a bit to the documentation to explain a way around this and
where apps need to be careful.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Dave Hansen <dave@sr71.net>
Link: http://lkml.kernel.org/r/20141212183835.8C581B3E@viggo.jf.intel.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---

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