From eaa5a990191d204ba0f9d35dbe5505ec2cdd1460 Mon Sep 17 00:00:00 2001 From: "H.J. Lu" Date: Fri, 26 Jul 2013 09:11:56 -0700 Subject: [PATCH] x86, fpu: correct the asm constraints for fxsave, unbreak mxcsr.daz MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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 Cc: --- 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 202d24f..5d576ab 100644 --- a/arch/x86/kernel/i387.c +++ b/arch/x86/kernel/i387.c @@ -116,7 +116,7 @@ static void mxcsr_feature_mask_init(void) 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; -- 2.7.4