Re: [PATCH] arm64: mm: support instruction SETEND

From: Suzuki K. Poulose
Date: Wed Jan 07 2015 - 05:10:43 EST


On 07/01/15 05:52, Leo Yan wrote:
Currently kernel has set the bit SCTLR_EL1.SED, so the SETEND
instruction will be treated as UNALLOCATED; this error can be
reproduced when ARMv8 cpu runs with EL1/aarch64 and EL0/aarch32
mode, finally kernel will trap the exception if the userspace
libs use SETEND instruction.

So this patch clears bit SCTLR_EL1.SED to support SETEND instruction.

The best way to do this, is via the instruction emulation framework added by Punit, which handles the armv8 deprecated/obsoleted instructions. This is now queued for 3.19.
I have a patchset which adds the 'SETEND' emulation support to the framework. This will enable better handling of the feature, including finding out the users of the deprecated instruction (when we switch to the emulation mode).

Btw, there is one open question that I am seeking answer for.

What should be the endianness of the signal handlers ? Should we leave it to the application ? Or restore the 'default' endianness for the signal handler ?


Thanks
Suzuki


Signed-off-by: Leo Yan <leo.yan@xxxxxxxxxx>
Signed-off-by: Xiaolong Ye <yexl@xxxxxxxxxxx>
---
arch/arm64/mm/proc.S | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
index 4e778b1..66a7363 100644
--- a/arch/arm64/mm/proc.S
+++ b/arch/arm64/mm/proc.S
@@ -249,9 +249,9 @@ ENDPROC(__cpu_setup)
* CE0 XWHW CZ ME TEEA S
* .... .IEE .... NEAI TE.I ..AD DEN0 ACAM
* 0011 0... 1101 ..0. ..0. 10.. .... .... < hardware reserved
- * .... .1.. .... 01.1 11.1 ..01 0001 1101 < software settings
+ * .... .1.. .... 01.1 11.1 ..00 0001 1101 < software settings
*/
.type crval, #object
crval:
- .word 0x000802e2 // clear
- .word 0x0405d11d // set
+ .word 0x000803e2 // clear
+ .word 0x0405d01d // set



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