decoder.cc revision 13759:9941fca869a9 
1/*
2 * Copyright (c) 2012-2014,2018 ARM Limited
3 * All rights reserved
4 *
5 * The license below extends only to copyright in the software and shall
6 * not be construed as granting a license to any other intellectual
7 * property including but not limited to intellectual property relating
8 * to a hardware implementation of the functionality of the software
9 * licensed hereunder.  You may use the software subject to the license
10 * terms below provided that you ensure that this notice is replicated
11 * unmodified and in its entirety in all distributions of the software,
12 * modified or unmodified, in source code or in binary form.
13 *
14 * Copyright (c) 2012 Google
15 * All rights reserved.
16 *
17 * Redistribution and use in source and binary forms, with or without
18 * modification, are permitted provided that the following conditions are
19 * met: redistributions of source code must retain the above copyright
20 * notice, this list of conditions and the following disclaimer;
21 * redistributions in binary form must reproduce the above copyright
22 * notice, this list of conditions and the following disclaimer in the
23 * documentation and/or other materials provided with the distribution;
24 * neither the name of the copyright holders nor the names of its
25 * contributors may be used to endorse or promote products derived from
26 * this software without specific prior written permission.
27 *
28 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
29 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
30 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
31 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
32 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
33 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
34 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
35 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
36 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
37 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
38 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
39 *
40 * Authors: Gabe Black
41 */
42
43#include "arch/arm/decoder.hh"
44
45#include "arch/arm/isa.hh"
46#include "arch/arm/isa_traits.hh"
47#include "arch/arm/utility.hh"
48#include "base/trace.hh"
49#include "debug/Decoder.hh"
50#include "sim/full_system.hh"
51
52namespace ArmISA
53{
54
55GenericISA::BasicDecodeCache Decoder::defaultCache;
56
57Decoder::Decoder(ISA* isa)
58    : data(0), fpscrLen(0), fpscrStride(0),
59      decoderFlavour(isa->decoderFlavour())
60{
61    reset();
62
63    // Initialize SVE vector length
64    sveLen = (isa->getCurSveVecLenInBitsAtReset() >> 7) - 1;
65}
66
67void
68Decoder::reset()
69{
70    bigThumb = false;
71    offset = 0;
72    emi = 0;
73    instDone = false;
74    outOfBytes = true;
75    foundIt = false;
76}
77
78void
79Decoder::process()
80{
81    // emi is typically ready, with some caveats below...
82    instDone = true;
83
84    if (!emi.thumb) {
85        emi.instBits = data;
86        if (!emi.aarch64) {
87            emi.sevenAndFour = bits(data, 7) && bits(data, 4);
88            emi.isMisc = (bits(data, 24, 23) == 0x2 &&
89                          bits(data, 20) == 0);
90        }
91        consumeBytes(4);
92        DPRINTF(Decoder, "Arm inst: %#x.\n", (uint64_t)emi);
93    } else {
94        uint16_t word = (data >> (offset * 8));
95        if (bigThumb) {
96            // A 32 bit thumb inst is half collected.
97            emi.instBits = emi.instBits | word;
98            bigThumb = false;
99            consumeBytes(2);
100            DPRINTF(Decoder, "Second half of 32 bit Thumb: %#x.\n",
101                    emi.instBits);
102        } else {
103            uint16_t highBits = word & 0xF800;
104            if (highBits == 0xE800 || highBits == 0xF000 ||
105                    highBits == 0xF800) {
106                // The start of a 32 bit thumb inst.
107                emi.bigThumb = 1;
108                if (offset == 0) {
109                    // We've got the whole thing.
110                    emi.instBits = (data >> 16) | (data << 16);
111                    DPRINTF(Decoder, "All of 32 bit Thumb: %#x.\n",
112                            emi.instBits);
113                    consumeBytes(4);
114                } else {
115                    // We only have the first half word.
116                    DPRINTF(Decoder,
117                            "First half of 32 bit Thumb.\n");
118                    emi.instBits = (uint32_t)word << 16;
119                    bigThumb = true;
120                    consumeBytes(2);
121                    // emi not ready yet.
122                    instDone = false;
123                }
124            } else {
125                // A 16 bit thumb inst.
126                consumeBytes(2);
127                emi.instBits = word;
128                // Set the condition code field artificially.
129                emi.condCode = COND_UC;
130                DPRINTF(Decoder, "16 bit Thumb: %#x.\n",
131                        emi.instBits);
132                if (bits(word, 15, 8) == 0xbf &&
133                        bits(word, 3, 0) != 0x0) {
134                    foundIt = true;
135                    itBits = bits(word, 7, 0);
136                    DPRINTF(Decoder,
137                            "IT detected, cond = %#x, mask = %#x\n",
138                            itBits.cond, itBits.mask);
139                }
140            }
141        }
142    }
143}
144
145void
146Decoder::consumeBytes(int numBytes)
147{
148    offset += numBytes;
149    assert(offset <= sizeof(MachInst) || emi.decoderFault);
150    if (offset == sizeof(MachInst))
151        outOfBytes = true;
152}
153
154void
155Decoder::moreBytes(const PCState &pc, Addr fetchPC, MachInst inst)
156{
157    data = inst;
158    offset = (fetchPC >= pc.instAddr()) ? 0 : pc.instAddr() - fetchPC;
159    emi.thumb = pc.thumb();
160    emi.aarch64 = pc.aarch64();
161    emi.fpscrLen = fpscrLen;
162    emi.fpscrStride = fpscrStride;
163    emi.sveLen = sveLen;
164
165    const Addr alignment(pc.thumb() ? 0x1 : 0x3);
166    emi.decoderFault = static_cast<uint8_t>(
167        pc.instAddr() & alignment ? DecoderFault::UNALIGNED : DecoderFault::OK);
168
169    outOfBytes = false;
170    process();
171}
172
173StaticInstPtr
174Decoder::decode(ArmISA::PCState &pc)
175{
176    if (!instDone)
177        return NULL;
178
179    const int inst_size((!emi.thumb || emi.bigThumb) ? 4 : 2);
180    ExtMachInst this_emi(emi);
181
182    pc.npc(pc.pc() + inst_size);
183    if (foundIt)
184        pc.nextItstate(itBits);
185    this_emi.itstate = pc.itstate();
186    this_emi.illegalExecution = pc.illegalExec() ? 1 : 0;
187
188    pc.size(inst_size);
189
190    emi = 0;
191    instDone = false;
192    foundIt = false;
193
194    return decode(this_emi, pc.instAddr());
195}
196
197}
198