* MIPS: math-emu: Fix jalr emulation when rd == $0
@ 2016-04-21 13:04 Paul Burton
0 siblings, 0 replies; 2+ messages in thread
From: Paul Burton @ 2016-04-21 13:04 UTC (permalink / raw)
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.burton@imgtec.com>
Cc: Maciej W. Rozycki <macro@imgtec.com>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/13160/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Kamal Mostafa <kamal@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
^ permalink raw reply related [flat|nested] 2+ messages in thread
* MIPS: math-emu: Fix jalr emulation when rd == $0
@ 2016-04-21 13:04 Paul Burton
0 siblings, 0 replies; 2+ messages in thread
From: Paul Burton @ 2016-04-21 13:04 UTC (permalink / raw)
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.burton@imgtec.com>
Cc: Maciej W. Rozycki <macro@imgtec.com>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/13160/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Kamal Mostafa <kamal@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 9dfcd7f..862bc86 100644
--- a/arch/mips/math-emu/cp1emu.c
+++ b/arch/mips/math-emu/cp1emu.c
@@ -443,9 +443,11 @@ 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:
*contpc = regs->regs[insn.r_format.rs];
--
2.7.4
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