From: H.J. Lu <hjl.tools@gmail.com>
Date: Fri, 26 Jul 2013 16:11:56 +0000 (-0700)
Subject: x86, fpu: correct the asm constraints for fxsave, unbreak mxcsr.daz
X-Git-Tag: v3.11-rc5~33^2~2
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=eaa5a990191d204ba0f9d35dbe5505ec2cdd1460;p=pandora-kernel.git

x86, fpu: correct the asm constraints for fxsave, unbreak mxcsr.daz

GCC will optimize mxcsr_feature_mask_init in arch/x86/kernel/i387.c:

		memset(&fx_scratch, 0, sizeof(struct i387_fxsave_struct));
		asm volatile("fxsave %0" : : "m" (fx_scratch));
		mask = fx_scratch.mxcsr_mask;
		if (mask == 0)
			mask = 0x0000ffbf;

to

		memset(&fx_scratch, 0, sizeof(struct i387_fxsave_struct));
		asm volatile("fxsave %0" : : "m" (fx_scratch));
		mask = 0x0000ffbf;

since asm statement doesn’t say it will update fx_scratch.  As the
result, the DAZ bit will be cleared.  This patch fixes it. This bug
dates back to at least kernel 2.6.12.

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Cc: <stable@vger.kernel.org>
---

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