| Date | Wed, 11 Sep 2013 00:29:41 -0400 | From | Steven Rostedt <> | Subject | [154/251] x86, fpu: correct the asm constraints for fxsave, unbreak mxcsr.daz |
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3.6.11.9-rc1 stable review patch. If anyone has any objections, please let me know.
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From: "H.J. Lu" <hjl.tools@gmail.com>
[ Upstream commit eaa5a990191d204ba0f9d35dbe5505ec2cdd1460 ]
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 doesnât 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> Signed-off-by: Steven Rostedt <rostedt@goodmis.org> --- arch/x86/kernel/i387.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c index f250431..6c5a7dc 100644 --- a/arch/x86/kernel/i387.c +++ b/arch/x86/kernel/i387.c @@ -132,7 +132,7 @@ static void __cpuinit mxcsr_feature_mask_init(void) clts(); if (cpu_has_fxsr) { memset(&fx_scratch, 0, sizeof(struct i387_fxsave_struct)); - asm volatile("fxsave %0" : : "m" (fx_scratch)); + asm volatile("fxsave %0" : "+m" (fx_scratch)); mask = fx_scratch.mxcsr_mask; if (mask == 0) mask = 0x0000ffbf; -- 1.7.10.4
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