src/arch/arm/decoder.cc

   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
  37 namespace ArmISA
  38 {
  39
  40 GenericISA::BasicDecodeCache Decoder::defaultCache;
  41
  42 void
  43 Decoder::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.
 109 void
 110 Decoder::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 }