decoder.cc revision 11165:d90aec9435bd 
1/*
2 * Copyright (c) 2012-2014 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
51namespace ArmISA
52{
53
54GenericISA::BasicDecodeCache Decoder::defaultCache;
55
56Decoder::Decoder(ISA* isa)
57    : data(0), fpscrLen(0), fpscrStride(0), decoderFlavour(isa
58            ? isa->decoderFlavour()
59            : Enums::Generic)
60{
61    reset();
62}
63
64void
65Decoder::reset()
66{
67    bigThumb = false;
68    offset = 0;
69    emi = 0;
70    instDone = false;
71    outOfBytes = true;
72    foundIt = false;
73}
74
75void
76Decoder::process()
77{
78    // emi is typically ready, with some caveats below...
79    instDone = true;
80
81    if (!emi.thumb) {
82        emi.instBits = data;
83        if (!emi.aarch64) {
84            emi.sevenAndFour = bits(data, 7) && bits(data, 4);
85            emi.isMisc = (bits(data, 24, 23) == 0x2 &&
86                          bits(data, 20) == 0);
87        }
88        consumeBytes(4);
89        DPRINTF(Decoder, "Arm inst: %#x.\n", (uint64_t)emi);
90    } else {
91        uint16_t word = (data >> (offset * 8));
92        if (bigThumb) {
93            // A 32 bit thumb inst is half collected.
94            emi.instBits = emi.instBits | word;
95            bigThumb = false;
96            consumeBytes(2);
97            DPRINTF(Decoder, "Second half of 32 bit Thumb: %#x.\n",
98                    emi.instBits);
99        } else {
100            uint16_t highBits = word & 0xF800;
101            if (highBits == 0xE800 || highBits == 0xF000 ||
102                    highBits == 0xF800) {
103                // The start of a 32 bit thumb inst.
104                emi.bigThumb = 1;
105                if (offset == 0) {
106                    // We've got the whole thing.
107                    emi.instBits = (data >> 16) | (data << 16);
108                    DPRINTF(Decoder, "All of 32 bit Thumb: %#x.\n",
109                            emi.instBits);
110                    consumeBytes(4);
111                } else {
112                    // We only have the first half word.
113                    DPRINTF(Decoder,
114                            "First half of 32 bit Thumb.\n");
115                    emi.instBits = (uint32_t)word << 16;
116                    bigThumb = true;
117                    consumeBytes(2);
118                    // emi not ready yet.
119                    instDone = false;
120                }
121            } else {
122                // A 16 bit thumb inst.
123                consumeBytes(2);
124                emi.instBits = word;
125                // Set the condition code field artificially.
126                emi.condCode = COND_UC;
127                DPRINTF(Decoder, "16 bit Thumb: %#x.\n",
128                        emi.instBits);
129                if (bits(word, 15, 8) == 0xbf &&
130                        bits(word, 3, 0) != 0x0) {
131                    foundIt = true;
132                    itBits = bits(word, 7, 0);
133                    DPRINTF(Decoder,
134                            "IT detected, cond = %#x, mask = %#x\n",
135                            itBits.cond, itBits.mask);
136                }
137            }
138        }
139    }
140}
141
142void
143Decoder::consumeBytes(int numBytes)
144{
145    offset += numBytes;
146    assert(offset <= sizeof(MachInst) || emi.decoderFault);
147    if (offset == sizeof(MachInst))
148        outOfBytes = true;
149}
150
151void
152Decoder::moreBytes(const PCState &pc, Addr fetchPC, MachInst inst)
153{
154    data = inst;
155    offset = (fetchPC >= pc.instAddr()) ? 0 : pc.instAddr() - fetchPC;
156    emi.thumb = pc.thumb();
157    emi.aarch64 = pc.aarch64();
158    emi.fpscrLen = fpscrLen;
159    emi.fpscrStride = fpscrStride;
160
161    const Addr alignment(pc.thumb() ? 0x1 : 0x3);
162    emi.decoderFault = static_cast<uint8_t>(
163        pc.instAddr() & alignment ? DecoderFault::UNALIGNED : DecoderFault::OK);
164
165    outOfBytes = false;
166    process();
167}
168
169StaticInstPtr
170Decoder::decode(ArmISA::PCState &pc)
171{
172    if (!instDone)
173        return NULL;
174
175    const int inst_size((!emi.thumb || emi.bigThumb) ? 4 : 2);
176    ExtMachInst this_emi(emi);
177
178    pc.npc(pc.pc() + inst_size);
179    if (foundIt)
180        pc.nextItstate(itBits);
181    this_emi.itstate = pc.itstate();
182    pc.size(inst_size);
183
184    emi = 0;
185    instDone = false;
186    foundIt = false;
187
188    return decode(this_emi, pc.instAddr());
189}
190
191}
192