| From | Ben Hutchings <> | Date | Sun, 08 Sep 2013 03:52:01 +0100 | Subject | [037/121] x86, fpu: correct the asm constraints for fxsave, unbreak mxcsr.daz |
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3.2.51-rc1 review patch. If anyone has any objections, please let me know.
------------------
From: "H.J. Lu" <hjl.tools@gmail.com>
commit eaa5a990191d204ba0f9d35dbe5505ec2cdd1460 upstream.
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> Signed-off-by: Ben Hutchings <ben@decadent.org.uk> --- arch/x86/kernel/i387.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/arch/x86/kernel/i387.c +++ b/arch/x86/kernel/i387.c @@ -51,7 +51,7 @@ void __cpuinit mxcsr_feature_mask_init(v 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; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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