gem5/src/arch/x86/predecoder.hh

/*
 * Copyright (c) 2007 The Hewlett-Packard Development Company
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 * this list of conditions and the following disclaimer.  Redistributions
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 * Non-Commercial Uses.  Derivatives of the software may be shared with
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 * and (ii) such Derivatives of the software include the above copyright
 * notice to acknowledge the contribution from this software where
 * applicable, this list of conditions and the disclaimer below.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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 * Authors: Gabe Black
 */

#ifndef __ARCH_X86_PREDECODER_HH__
#define __ARCH_X86_PREDECODER_HH__

#include "arch/x86/types.hh"
#include "sim/host.hh"

class ThreadContext;

namespace X86ISA
{
    class Predecoder
    {
      private:
        //These are defined and documented in predecoder_tables.cc
        static const uint8_t Prefixes[256];
        static const uint8_t UsesModRM[2][256];
        static const uint8_t ImmediateType[2][256];
        static const uint8_t ImmediateTypeToSize[3][10];

      protected:
        ThreadContext * tc;
        //The bytes to be predecoded
        MachInst fetchChunk;
        //The pc of the start of fetchChunk
        Addr basePC;
        //The offset into fetchChunk of current processing
        int offset;
        //The extended machine instruction being generated
        ExtMachInst emi;

        //State machine state
      protected:
        //Whether or not we're out of bytes
        bool outOfBytes;
        //Whether we've completed generating an ExtMachInst
        bool emiIsReady;
        //The size of the displacement value
        int displacementSize;
        int displacementCollected;
        //The size of the immediate value
        int immediateSize;
        int immediateCollected;

        //These are local to some of the states. I need to turn the states
        //into inline functions to clean things up a bit.
        int toGet;
        int remaining;
        MachInst partialDisp;

        enum State {
            Prefix,
            Opcode,
            ModRM,
            SIB,
            Displacement,
            Immediate
        };

        State state;

      public:
        Predecoder(ThreadContext * _tc) :
            tc(_tc), basePC(0), offset(0),
            outOfBytes(true), emiIsReady(false),
            state(Prefix)
        {}

        ThreadContext * getTC()
        {
            return tc;
        }

        void setTC(ThreadContext * _tc)
        {
            tc = _tc;
        }

        void process();

        //Use this to give data to the predecoder. This should be used
        //when there is control flow.
        void moreBytes(Addr currPC, Addr off, MachInst data)
        {
            basePC = currPC;
            offset = off;
            fetchChunk = data;
            assert(off < sizeof(MachInst));
            outOfBytes = false;
            process();
        }

        //Use this to give data to the predecoder. This should be used
        //when instructions are executed in order.
        void moreBytes(MachInst machInst)
        {
            moreBytes(basePC + sizeof(machInst), 0, machInst);
        }

        bool needMoreBytes()
        {
            return outOfBytes;
        }

        bool extMachInstReady()
        {
            return emiIsReady;
        }

        //This returns a constant reference to the ExtMachInst to avoid a copy
        const ExtMachInst & getExtMachInst()
        {
            assert(emiIsReady);
            emiIsReady = false;
            return emi;
        }
    };
};

#endif // __ARCH_X86_PREDECODER_HH__