qemu-e2k/target/arm/m-nocp.decode
Peter Maydell 5d2555a1fe target/arm: Implement v8.1M NOCP handling
From v8.1M, disabled-coprocessor handling changes slightly:
 * coprocessors 8, 9, 14 and 15 are also governed by the
   cp10 enable bit, like cp11
 * an extra range of instruction patterns is considered
   to be inside the coprocessor space

We previously marked these up with TODO comments; implement the
correct behaviour.

Unfortunately there is no ID register field which indicates this
behaviour.  We could in theory test an unrelated ID register which
indicates guaranteed-to-be-in-v8.1M behaviour like ID_ISAR0.CmpBranch
>= 3 (low-overhead-loops), but it seems better to simply define a new
ARM_FEATURE_V8_1M feature flag and use it for this and other
new-in-v8.1M behaviour that isn't identifiable from the ID registers.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20201019151301.2046-3-peter.maydell@linaro.org
2020-10-20 16:12:01 +01:00

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# M-profile UserFault.NOCP exception handling
#
# Copyright (c) 2020 Linaro, Ltd
#
# This library is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
# License as published by the Free Software Foundation; either
# version 2.1 of the License, or (at your option) any later version.
#
# This library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
# Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public
# License along with this library; if not, see <http://www.gnu.org/licenses/>.
#
# This file is processed by scripts/decodetree.py
#
# For M-profile, the architecture specifies that NOCP UsageFaults
# should take precedence over UNDEF faults over the whole wide
# range of coprocessor-space encodings, with the exception of
# VLLDM and VLSTM. (Compare v8.1M IsCPInstruction() pseudocode and
# v8M Arm ARM rule R_QLGM.) This isn't mandatory for v8.0M but we choose
# to behave the same as v8.1M.
# This decode is handled before any others (and in particular before
# decoding FP instructions which are in the coprocessor space).
# If the coprocessor is not present or disabled then we will generate
# the NOCP exception; otherwise we let the insn through to the main decode.
&nocp cp
{
# Special cases which do not take an early NOCP: VLLDM and VLSTM
VLLDM_VLSTM 1110 1100 001 l:1 rn:4 0000 1010 0000 0000
# TODO: VSCCLRM (new in v8.1M) is similar:
#VSCCLRM 1110 1100 1-01 1111 ---- 1011 ---- ---0
NOCP 111- 1110 ---- ---- ---- cp:4 ---- ---- &nocp
NOCP 111- 110- ---- ---- ---- cp:4 ---- ---- &nocp
# From v8.1M onwards this range will also NOCP:
NOCP_8_1 111- 1111 ---- ---- ---- ---- ---- ---- &nocp cp=10
}