Re: Linux Sparc FPU register corruption
From: David Miller <davem@davemloft.net>
Date: Tue, 09 Jun 2015 00:34:14 -0700 (PDT)
> Your test is faulty.
>
> You cannot use ASI_BLK_P loads or stores without appropriate memory
> barriers around them.
Um, but my test isn't testing what is being stored to memory at all. It is storing to memory and **never loading from the memory after**. Why would writing FROM fp registers TO memory corrupt the *registers* due to a missing memory barrier?
If problem 1 is due to a missing membar somewhere, I think it's surely gotta be the kernel that's missing it, not my test code. No?
> FWIW, you're probably hitting the bug fixed by the following commit in
> glibc:
>
> commit 834caf06f33d79be54cff63c274fba2845513593
> Author: Jose E. Marchesi <jose.marchesi@oracle.com>
> Date: Sat May 17 11:20:27 2014 -0700
>
> Fix sparc memcpy data corruption when using niagara2 optimized routines.
>
> * sysdeps/sparc/sparc64/multiarch/memcpy-niagara2.S: Add missing
> membar to avoid block loads/stores to overlap previous stores.
>
Debian glibc has multiarch support disabled (done a couple years ago to try to workaround the unreliability, not entirely successfully..), so it's not using that routine you mention. It's using sysdeps/sparc/sparc32/sparcv9/memcpy.S which points to sysdeps/sparc/sparc64/memcpy.S
[sorry for the duplicate post -- didn't realize vger.kernel.org doesn't accept emails sent by the android gmail client]
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