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authorH.J. Lu <hjl.tools@gmail.com>2013-07-26 09:11:56 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2013-08-11 18:35:24 -0700
commit62fda513d368032d8f6b0375004032d5c0c6060d (patch)
tree42bc0b0d92c6a722c20dce45ae73c3aee22bdc1f /arch
parent8ecbcde519f31f5ac76cfe34c99369da1c8a1d2c (diff)
x86, fpu: correct the asm constraints for fxsave, unbreak mxcsr.daz
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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'arch')
-rw-r--r--arch/x86/kernel/i387.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c
index cb339097b9e..f7ea30dce23 100644
--- a/arch/x86/kernel/i387.c
+++ b/arch/x86/kernel/i387.c
@@ -116,7 +116,7 @@ static void __cpuinit 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;