Patch "MIPS: math-emu: Fix jalr emulation when rd == $0" has been added to the 3.14-stable tree

This is a note to let you know that I've just added the patch titled

    MIPS: math-emu: Fix jalr emulation when rd == $0

to the 3.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
mips-math-emu-fix-jalr-emulation-when-rd-0.patch
and it can be found in the queue-3.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Paul Burton <[email protected]>
Date: Thu, 21 Apr 2016 14:04:55 +0100
Subject: MIPS: math-emu: Fix jalr emulation when rd == $0

From: Paul Burton <[email protected]>

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.

Patchwork: https://patchwork.linux-mips.org/patch/13160/

---
 arch/mips/math-emu/cp1emu.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

@@ -676,9 +676,11 @@ static int isBranchInstr(struct pt_regs
 	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:
 			*contpc = regs->regs[insn.r_format.rs];

Patches currently in stable-queue which might be from [email protected] are

queue-3.14/mips-math-emu-fix-jalr-emulation-when-rd-0.patch