[3.16.y-ckt stable] Patch "xtensa: fix kernel register spilling" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    xtensa: fix kernel register spilling

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt18.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From a1668e168b90d192420cd54716a01dfaf737a911 Mon Sep 17 00:00:00 2001
From: Max Filippov <jcmvbkbc at gmail.com>
Date: Thu, 16 Jul 2015 10:41:02 +0300
Subject: xtensa: fix kernel register spilling

commit 77d6273e79e3a86552fcf10cdd31a69b46ed2ce6 upstream.

call12 can't be safely used as the first call in the inline function,
because the compiler does not extend the stack frame of the bounding
function accordingly, which may result in corruption of local variables.

If a call needs to be done, do call8 first followed by call12.

For pure assembly code in _switch_to increase stack frame size of the
bounding function.

Signed-off-by: Max Filippov <jcmvbkbc at gmail.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 arch/xtensa/include/asm/traps.h | 29 +++++++++++++++++++----------
 arch/xtensa/kernel/entry.S      |  4 ++--
 2 files changed, 21 insertions(+), 12 deletions(-)

diff --git a/arch/xtensa/include/asm/traps.h b/arch/xtensa/include/asm/traps.h
index 677bfcf4ee5d..28f33a8b7f5f 100644
--- a/arch/xtensa/include/asm/traps.h
+++ b/arch/xtensa/include/asm/traps.h
@@ -25,30 +25,39 @@ static inline void spill_registers(void)
 {
 #if XCHAL_NUM_AREGS > 16
 	__asm__ __volatile__ (
-		"	call12	1f\n"
+		"	call8	1f\n"
 		"	_j	2f\n"
 		"	retw\n"
 		"	.align	4\n"
 		"1:\n"
+#if XCHAL_NUM_AREGS == 32
+		"	_entry	a1, 32\n"
+		"	addi	a8, a0, 3\n"
+		"	_entry	a1, 16\n"
+		"	mov	a12, a12\n"
+		"	retw\n"
+#else
 		"	_entry	a1, 48\n"
-		"	addi	a12, a0, 3\n"
-#if XCHAL_NUM_AREGS > 32
-		"	.rept	(" __stringify(XCHAL_NUM_AREGS) " - 32) / 12\n"
+		"	call12	1f\n"
+		"	retw\n"
+		"	.align	4\n"
+		"1:\n"
+		"	.rept	(" __stringify(XCHAL_NUM_AREGS) " - 16) / 12\n"
 		"	_entry	a1, 48\n"
 		"	mov	a12, a0\n"
 		"	.endr\n"
-#endif
-		"	_entry	a1, 48\n"
+		"	_entry	a1, 16\n"
 #if XCHAL_NUM_AREGS % 12 == 0
-		"	mov	a8, a8\n"
-#elif XCHAL_NUM_AREGS % 12 == 4
 		"	mov	a12, a12\n"
-#elif XCHAL_NUM_AREGS % 12 == 8
+#elif XCHAL_NUM_AREGS % 12 == 4
 		"	mov	a4, a4\n"
+#elif XCHAL_NUM_AREGS % 12 == 8
+		"	mov	a8, a8\n"
 #endif
 		"	retw\n"
+#endif
 		"2:\n"
-		: : : "a12", "a13", "memory");
+		: : : "a8", "a9", "memory");
 #else
 	__asm__ __volatile__ (
 		"	mov	a12, a12\n"
diff --git a/arch/xtensa/kernel/entry.S b/arch/xtensa/kernel/entry.S
index 8a749f02d8d6..cf8a354fa628 100644
--- a/arch/xtensa/kernel/entry.S
+++ b/arch/xtensa/kernel/entry.S
@@ -1793,7 +1793,7 @@ ENDPROC(system_call)
 	mov	a12, a0
 	.endr
 #endif
-	_entry	a1, 48
+	_entry	a1, 16
 #if XCHAL_NUM_AREGS % 12 == 0
 	mov	a8, a8
 #elif XCHAL_NUM_AREGS % 12 == 4
@@ -1817,7 +1817,7 @@ ENDPROC(system_call)

 ENTRY(_switch_to)

-	entry	a1, 16
+	entry	a1, 48

 	mov	a11, a3			# and 'next' (a3)