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

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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: 102cedc32a ("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
Cc: stable <stable@vger.kernel.org> # v3.10
Patchwork: https://patchwork.linux-mips.org/patch/13160/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
This commit is contained in:
Paul Burton 2016-04-21 14:04:55 +01:00 committed by Ralf Baechle
parent db57f29d50
commit ab4a92e667
1 changed files with 5 additions and 3 deletions
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8
arch/mips/math-emu/cp1emu.c
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@ -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 */