decoder.cc revision 9377:6f294e7a93d1 
1/*
2 * Copyright (c) 2012 Google
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions are
7 * met: redistributions of source code must retain the above copyright
8 * notice, this list of conditions and the following disclaimer;
9 * redistributions in binary form must reproduce the above copyright
10 * notice, this list of conditions and the following disclaimer in the
11 * documentation and/or other materials provided with the distribution;
12 * neither the name of the copyright holders nor the names of its
13 * contributors may be used to endorse or promote products derived from
14 * this software without specific prior written permission.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
17 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
18 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
19 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
20 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
21 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
22 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
23 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
24 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
25 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
26 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27 *
28 * Authors: Gabe Black
29 */
30
31#include "arch/arm/decoder.hh"
32#include "arch/arm/isa_traits.hh"
33#include "arch/arm/utility.hh"
34#include "base/trace.hh"
35#include "debug/Decoder.hh"
36
37namespace ArmISA
38{
39
40GenericISA::BasicDecodeCache Decoder::defaultCache;
41
42void
43Decoder::process()
44{
45    // emi is typically ready, with some caveats below...
46    instDone = true;
47
48    if (!emi.thumb) {
49        emi.instBits = data;
50        emi.sevenAndFour = bits(data, 7) && bits(data, 4);
51        emi.isMisc = (bits(data, 24, 23) == 0x2 &&
52                      bits(data, 20) == 0);
53        consumeBytes(4);
54        DPRINTF(Decoder, "Arm inst: %#x.\n", (uint64_t)emi);
55    } else {
56        uint16_t word = (data >> (offset * 8));
57        if (bigThumb) {
58            // A 32 bit thumb inst is half collected.
59            emi.instBits = emi.instBits | word;
60            bigThumb = false;
61            consumeBytes(2);
62            DPRINTF(Decoder, "Second half of 32 bit Thumb: %#x.\n",
63                    emi.instBits);
64        } else {
65            uint16_t highBits = word & 0xF800;
66            if (highBits == 0xE800 || highBits == 0xF000 ||
67                    highBits == 0xF800) {
68                // The start of a 32 bit thumb inst.
69                emi.bigThumb = 1;
70                if (offset == 0) {
71                    // We've got the whole thing.
72                    emi.instBits = (data >> 16) | (data << 16);
73                    DPRINTF(Decoder, "All of 32 bit Thumb: %#x.\n",
74                            emi.instBits);
75                    consumeBytes(4);
76                } else {
77                    // We only have the first half word.
78                    DPRINTF(Decoder,
79                            "First half of 32 bit Thumb.\n");
80                    emi.instBits = (uint32_t)word << 16;
81                    bigThumb = true;
82                    consumeBytes(2);
83                    // emi not ready yet.
84                    instDone = false;
85                }
86            } else {
87                // A 16 bit thumb inst.
88                consumeBytes(2);
89                emi.instBits = word;
90                // Set the condition code field artificially.
91                emi.condCode = COND_UC;
92                DPRINTF(Decoder, "16 bit Thumb: %#x.\n",
93                        emi.instBits);
94                if (bits(word, 15, 8) == 0xbf &&
95                        bits(word, 3, 0) != 0x0) {
96                    foundIt = true;
97                    itBits = bits(word, 7, 0);
98                    DPRINTF(Decoder,
99                            "IT detected, cond = %#x, mask = %#x\n",
100                            itBits.cond, itBits.mask);
101                }
102            }
103        }
104    }
105}
106
107//Use this to give data to the decoder. This should be used
108//when there is control flow.
109void
110Decoder::moreBytes(const PCState &pc, Addr fetchPC, MachInst inst)
111{
112    data = inst;
113    offset = (fetchPC >= pc.instAddr()) ? 0 : pc.instAddr() - fetchPC;
114    emi.thumb = pc.thumb();
115    emi.fpscrLen = fpscrLen;
116    emi.fpscrStride = fpscrStride;
117
118    outOfBytes = false;
119    process();
120}
121
122}
123