src/cpu/core_prefetch_8086.cpp

/*
 *  Copyright (C) 2002-2020  The DOSBox Team
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License along
 *  with this program; if not, write to the Free Software Foundation, Inc.,
 *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 */


#include <stdio.h>
#include <string.h>

#include "dosbox.h"
#include "mem.h"
#include "cpu.h"
#include "lazyflags.h"
#include "inout.h"
#include "callback.h"
#include "pic.h"
#include "fpu.h"
#include "paging.h"
#include "mmx.h"

using namespace std;

#include <algorithm>

#define CPU_CORE CPU_ARCHTYPE_8086
#define CPU_Core_Prefetch_Trap_Run CPU_Core8086_Prefetch_Trap_Run

#define DoString DoString_Prefetch8086

extern bool ignore_opcode_63;

#if C_DEBUG
#include "debug.h"
#endif

static Bit16u last_ea86_offset;

/* NTS: we special case writes to seg:ffff to emulate 8086 behavior where word read/write wraps around the 64KB segment */
#if (!C_CORE_INLINE)

#define LoadMb(off) mem_readb(off)

static inline Bit16u LoadMw(Bitu off) {
        if (last_ea86_offset == 0xffff)
                return (mem_readb(off) | (mem_readb(off-0xffff) << 8));

        return mem_readw(off);  
}

#define LoadMd(off) mem_readd(off)

#define SaveMb(off,val) mem_writeb(off,val)

static void SaveMw(Bitu off,Bitu val) {
        if (last_ea86_offset == 0xffff) {
                mem_writeb(off,val);
                mem_writeb(off-0xffff,val>>8);
        }
        else {
                mem_writew(off,val);
        }
}

#define SaveMd(off,val) mem_writed(off,val)

#else 

#include "paging.h"

#define LoadMb(off) mem_readb_inline(off)

static inline Bit16u LoadMw(Bitu off) {
        if (last_ea86_offset == 0xffff)
                return (mem_readb_inline((PhysPt)off) | (mem_readb_inline((PhysPt)(off-0xffff)) << 8));

        return mem_readw_inline((PhysPt)off);
}

#define LoadMd(off) mem_readd_inline(off)

#define SaveMb(off,val) mem_writeb_inline(off,val)

static void SaveMw(Bitu off,Bitu val) {
        if (last_ea86_offset == 0xffff) {
                mem_writeb_inline((PhysPt)off,(Bit8u)val);
                mem_writeb_inline((PhysPt)(off-0xffff),(Bit8u)(val>>8));
        }
        else {
                mem_writew_inline((PhysPt)off,(Bit16u)val);
        }
}

#define SaveMd(off,val) mem_writed_inline(off,val)

#endif

extern Bitu cycle_count;

#if C_FPU
#define CPU_FPU 1u                                              //Enable FPU escape instructions
#endif

#define CPU_PIC_CHECK 1u
#define CPU_TRAP_CHECK 1u

#define OPCODE_NONE                     0x000u
#define OPCODE_0F                       0x100u

#define OPCODE_SIZE                     0u          //DISABLED

#define PREFIX_ADDR                     0u                      //DISABLED

#define PREFIX_REP                      0x2u

#define TEST_PREFIX_ADDR        (0u)
#define TEST_PREFIX_REP         (core.prefixes & PREFIX_REP)

#define DO_PREFIX_SEG(_SEG)                                     \
    if (GETFLAG(IF) && CPU_Cycles <= 0) goto prefix_out; \
        BaseDS=SegBase(_SEG);                                   \
        BaseSS=SegBase(_SEG);                                   \
        core.base_val_ds=_SEG;                                  \
        goto restart_opcode;

// it's the core's job not to decode 0x66-0x67 when compiled for 8086
#define DO_PREFIX_ADDR()                                                                \
    abort();

#define DO_PREFIX_REP(_ZERO)                            \
    if (GETFLAG(IF) && CPU_Cycles <= 0) goto prefix_out; \
        core.prefixes|=PREFIX_REP;                              \
        core.rep_zero=_ZERO;                                    \
        goto restart_opcode;

typedef PhysPt (*GetEAHandler)(void);

static const Bit32u AddrMaskTable[2]={0x0000ffffu,0x0000ffffu};

static struct {
        Bitu opcode_index;
        PhysPt cseip;
        PhysPt base_ds,base_ss;
        SegNames base_val_ds;
        bool rep_zero;
        Bitu prefixes;
        GetEAHandler * ea_table;
} core;

#define GETIP           (core.cseip-SegBase(cs))
#define SAVEIP          reg_eip=GETIP;
#define LOADIP          core.cseip=(SegBase(cs)+reg_eip);

#define SAVEIP_PREFIX           reg_eip=GETIP-1;

#define SegBase(c)      SegPhys(c)
#define BaseDS          core.base_ds
#define BaseSS          core.base_ss

//#define PREFETCH_DEBUG

#define MAX_PQ_SIZE 32
static Bit8u prefetch_buffer[MAX_PQ_SIZE];
static bool pq_valid=false;
static Bitu pq_start;
static Bitu pq_fill;
static Bitu pq_limit;
static Bitu pq_reload;
#ifdef PREFETCH_DEBUG
static double pq_next_dbg=0;
static unsigned int pq_hit=0,pq_miss=0;
#endif

/* MUST BE POWER OF 2 */
#define prefetch_unit       (2ul)

#include "core_prefetch_buf.h"

static INLINE void FetchDiscardb() {
        FetchDiscard<uint8_t>();
}

static INLINE Bit8u FetchPeekb() {
        return FetchPeek<uint8_t>();
}

static Bit8u Fetchb() {
        return Fetch<uint8_t>();
}

static Bit16u Fetchw() {
        return Fetch<uint16_t>();
}

static Bit32u Fetchd() {
        return Fetch<uint32_t>();
}

#define Push_16 CPU_Push16
#define Pop_16 CPU_Pop16

#include "instructions.h"
#include "core_normal/support.h"
#include "core_normal/string.h"


#define EALookupTable (core.ea_table)

void CPU_Core8086_Prefetch_reset(void) {
    pq_valid=false;
    prefetch_init(0);
#ifdef PREFETCH_DEBUG
    pq_next_dbg=0;
#endif
}

Bits CPU_Core8086_Prefetch_Run(void) {
        bool invalidate_pq=false;

    if (CPU_Cycles <= 0)
            return CBRET_NONE;

    pq_limit = (max(CPU_PrefetchQueueSize,(unsigned int)(4ul + prefetch_unit)) + prefetch_unit - 1ul) & (~(prefetch_unit-1ul));
    pq_reload = min(pq_limit,(Bitu)8u);

        while (CPU_Cycles-->0) {
                if (invalidate_pq) {
                        pq_valid=false;
                        invalidate_pq=false;
                }
                LOADIP;
                core.prefixes=0;
                core.opcode_index=0;
                last_ea86_offset=0;
                core.ea_table=&EATable[0];
                BaseDS=SegBase(ds);
                BaseSS=SegBase(ss);
                core.base_val_ds=ds;
#if C_DEBUG
#if C_HEAVY_DEBUG
                if (DEBUG_HeavyIsBreakpoint()) {
                        FillFlags();
                        return (Bits)debugCallback;
                }
#endif
                cycle_count++;
#endif
restart_opcode:
                Bit8u next_opcode=Fetchb();
                invalidate_pq=false;
                if (core.opcode_index&OPCODE_0F) invalidate_pq=true;
                else switch (next_opcode) {
                        case 0x70:      case 0x71:      case 0x72:      case 0x73:
                        case 0x74:      case 0x75:      case 0x76:      case 0x77:
                        case 0x78:      case 0x79:      case 0x7a:      case 0x7b:
                        case 0x7c:      case 0x7d:      case 0x7e:      case 0x7f:      // jcc
                        case 0x9a:      // call
                        case 0xc2:      case 0xc3:      // retn
                        case 0xc8:      // enter
                        case 0xc9:      // leave
                        case 0xca:      case 0xcb:      // retf
                        case 0xcc:      // int3
                        case 0xcd:      // int
                        case 0xce:      // into
                        case 0xcf:      // iret
                        case 0xe0:      // loopnz
                        case 0xe1:      // loopz
                        case 0xe2:      // loop
                        case 0xe3:      // jcxz
                        case 0xe8:      // call
                        case 0xe9:      case 0xea:      case 0xeb:      // jmp
                        case 0xff:
                                invalidate_pq=true;
                                break;
                        default:
                                break;
                }
                switch (core.opcode_index+next_opcode) {
                #include "core_normal/prefix_none.h"
                default:
                illegal_opcode:
#if C_DEBUG
                        {
                                bool ignore=false;
                                Bitu len=(GETIP-reg_eip);
                                LOADIP;
                                if (len>16) len=16;
                                char tempcode[16*2+1];char * writecode=tempcode;
                                if (ignore_opcode_63 && mem_readb(core.cseip) == 0x63)
                                        ignore = true;
                                for (;len>0;len--) {
                                        sprintf(writecode,"%02X",mem_readb(core.cseip++));
                                        writecode+=2;
                                }
                                if (!ignore)
                                        LOG(LOG_CPU,LOG_NORMAL)("Illegal/Unhandled opcode %s",tempcode);
                        }
#endif
                        /* there is no invalid opcode instruction. */
                        reg_eip += 2;
                        continue;
                }
                SAVEIP;
        }

#ifdef PREFETCH_DEBUG
    if (PIC_FullIndex() > pq_next_dbg) {
        LOG_MSG("Prefetch core debug: prefetch cache hit=%u miss=%u",pq_hit,pq_miss);
        pq_next_dbg += 500.0;
    }
#endif

        FillFlags();
        return CBRET_NONE;
/* 8086/286 multiple prefix interrupt bug emulation.
 * If an instruction is interrupted, only the last prefix is restarted.
 * See also [https://www.pcjs.org/pubs/pc/reference/intel/8086/] and [https://www.youtube.com/watch?v=6FC-tcwMBnU] */ 
prefix_out:
        SAVEIP_PREFIX;
        FillFlags();
        return CBRET_NONE;
decode_end:
        SAVEIP;
        FillFlags();
        return CBRET_NONE;
}

Bits CPU_Core_Prefetch_Trap_Run(void) {
        Bits oldCycles = CPU_Cycles;
        CPU_Cycles = 1;
        cpu.trap_skip = false;

        Bits ret=CPU_Core_Prefetch_Run();
        if (!cpu.trap_skip) CPU_HW_Interrupt(1);
        CPU_Cycles = oldCycles-1;
        cpudecoder = &CPU_Core_Prefetch_Run;

        return ret;
}