This is a note to let you know that I have just added a patch titled
MIPS: math-emu: Fix jalr emulation when rd == $0
to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree
which can be found at:
https://git.launchpad.net/~canonical-kernel/linux/+git/linux-stable-ckt/log/?h=linux-4.2.y-queue
This patch is scheduled to be released in version 4.2.8-ckt12.
If you, or anyone else, feels it should not be added to this tree, please
reply to this email.
For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable
Thanks.
-Kamal
---8<------------------------------------------------------------
>From e4a68a824140f11f989e262c1929658b2b179e95 Mon Sep 17 00:00:00 2001
From: Paul Burton <paul.bur...@imgtec.com>
Date: Thu, 21 Apr 2016 14:04:55 +0100
Subject: MIPS: math-emu: Fix jalr emulation when rd == $0
commit ab4a92e66741b35ca12f8497896bafbe579c28a1 upstream.
When emulating a jalr instruction with rd == $0, the code in
isBranchInstr was incorrectly writing to GPR $0 which should actually
always remain zeroed. This would lead to any further instructions
emulated which use $0 operating on a bogus value until the task is next
context switched, at which point the value of $0 in the task context
would be restored to the correct zero by a store in SAVE_SOME. Fix this
by not writing to rd if it is $0.
Fixes: 102cedc32a6e ("MIPS: microMIPS: Floating point support.")
Signed-off-by: Paul Burton <paul.bur...@imgtec.com>
Cc: Maciej W. Rozycki <ma...@imgtec.com>
Cc: James Hogan <james.ho...@imgtec.com>
Cc: linux-m...@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/13160/
Signed-off-by: Ralf Baechle <r...@linux-mips.org>
Signed-off-by: Kamal Mostafa <ka...@canonical.com>
---
arch/mips/math-emu/cp1emu.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/arch/mips/math-emu/cp1emu.c b/arch/mips/math-emu/cp1emu.c
index f0f1b98..2bf9209 100644
--- a/arch/mips/math-emu/cp1emu.c
+++ b/arch/mips/math-emu/cp1emu.c
@@ -445,9 +445,11 @@ static int isBranchInstr(struct pt_regs *regs, struct
mm_decoded_insn dec_insn,
case spec_op:
switch (insn.r_format.func) {
case jalr_op:
- regs->regs[insn.r_format.rd] =
- regs->cp0_epc + dec_insn.pc_inc +
- dec_insn.next_pc_inc;
+ if (insn.r_format.rd != 0) {
+ regs->regs[insn.r_format.rd] =
+ regs->cp0_epc + dec_insn.pc_inc +
+ dec_insn.next_pc_inc;
+ }
/* Fall through */
case jr_op:
/* For R6, JR already emulated in jalr_op */
--
2.7.4
