Commit-ID: eaa5a990191d204ba0f9d35dbe5505ec2cdd1460
Gitweb: http://git.kernel.org/tip/eaa5a990191d204ba0f9d35dbe5505ec2cdd1460
Author: H.J. Lu <[email protected]>
AuthorDate: Fri, 26 Jul 2013 09:11:56 -0700
Committer: H. Peter Anvin <[email protected]>
CommitDate: Fri, 26 Jul 2013 09:11:56 -0700
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 <[email protected]>
Cc: <[email protected]>
---
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;
--
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