NASM 0.93

[nasm.git] / assemble.c

/* assemble.c   code generation for the Netwide Assembler
 *
 * The Netwide Assembler is copyright (C) 1996 Simon Tatham and
 * Julian Hall. All rights reserved. The software is
 * redistributable under the licence given in the file "Licence"
 * distributed in the NASM archive.
 *
 * the actual codes (C syntax, i.e. octal):
 * \0            - terminates the code. (Unless it's a literal of course.)
 * \1, \2, \3    - that many literal bytes follow in the code stream
 * \4, \6        - the POP/PUSH (respectively) codes for CS, DS, ES, SS
 *                 (POP is never used for CS) depending on operand 0
 * \5, \7        - the second byte of POP/PUSH codes for FS, GS, depending
 *                 on operand 0
 * \10, \11, \12 - a literal byte follows in the code stream, to be added
 *                 to the register value of operand 0, 1 or 2
 * \17           - encodes the literal byte 0. (Some compilers don't take
 *                 kindly to a zero byte in the _middle_ of a compile time
 *                 string constant, so I had to put this hack in.)
 * \14, \15, \16 - a signed byte immediate operand, from operand 0, 1 or 2
 * \20, \21, \22 - a byte immediate operand, from operand 0, 1 or 2
 * \24, \25, \26 - an unsigned byte immediate operand, from operand 0, 1 or 2
 * \30, \31, \32 - a word immediate operand, from operand 0, 1 or 2
 * \34, \35, \36 - select between \3[012] and \4[012] depending on 16/32 bit
 *                 assembly mode or the address-size override on the operand
 * \37           - a word constant, from the _segment_ part of operand 0
 * \40, \41, \42 - a long immediate operand, from operand 0, 1 or 2
 * \50, \51, \52 - a byte relative operand, from operand 0, 1 or 2
 * \60, \61, \62 - a word relative operand, from operand 0, 1 or 2
 * \64, \65, \66 - select between \6[012] and \7[012] depending on 16/32 bit
 *                 assembly mode or the address-size override on the operand
 * \70, \71, \72 - a long relative operand, from operand 0, 1 or 2
 * \1ab          - a ModRM, calculated on EA in operand a, with the spare
 *                 field the register value of operand b.
 * \2ab          - a ModRM, calculated on EA in operand a, with the spare
 *                 field equal to digit b.
 * \30x          - might be an 0x67 byte, depending on the address size of
 *                 the memory reference in operand x.
 * \310          - indicates fixed 16-bit address size, i.e. optional 0x67.
 * \311          - indicates fixed 32-bit address size, i.e. optional 0x67.
 * \320          - indicates fixed 16-bit operand size, i.e. optional 0x66.
 * \321          - indicates fixed 32-bit operand size, i.e. optional 0x66.
 * \322          - indicates that this instruction is only valid when the
 *                 operand size is the default (instruction to disassembler,
 *                 generates no code in the assembler)
 * \330          - a literal byte follows in the code stream, to be added
 *                 to the condition code value of the instruction.
 * \340          - reserve <operand 0> bytes of uninitialised storage.
 *                 Operand 0 had better be a segmentless constant.
 */

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

#include "nasm.h"
#include "assemble.h"
#include "insns.h"

extern struct itemplate *nasm_instructions[];

typedef struct {
    int sib_present;                   /* is a SIB byte necessary? */
    int bytes;                         /* # of bytes of offset needed */
    int size;                          /* lazy - this is sib+bytes+1 */
    unsigned char modrm, sib;          /* the bytes themselves */
} ea;

static efunc errfunc;
static struct ofmt *outfmt;

static long calcsize (long, long, int, insn *, char *);
static void gencode (long, long, int, insn *, char *, long);
static int regval (operand *o);
static int matches (struct itemplate *, insn *);
static ea *process_ea (operand *, ea *, int, int, int);
static int chsize (operand *, int);

long assemble (long segment, long offset, int bits,
               insn *instruction, struct ofmt *output, efunc error) {
    int j, itimes, size_prob;
    long insn_end;
    long start = offset;
    struct itemplate *temp;

    errfunc = error;                   /* to pass to other functions */
    outfmt = output;                   /* likewise */

    if (instruction->opcode == -1)
        return 0;

    if (instruction->opcode == I_DB ||
        instruction->opcode == I_DW ||
        instruction->opcode == I_DD ||
        instruction->opcode == I_DQ ||
        instruction->opcode == I_DT) {
        extop *e;
        long osize, wsize = 0;         /* placate gcc */
        int t = instruction->times;

        switch (instruction->opcode) {
          case I_DB: wsize = 1; break;
          case I_DW: wsize = 2; break;
          case I_DD: wsize = 4; break;
          case I_DQ: wsize = 8; break;
          case I_DT: wsize = 10; break;
        }

        while (t--) {
            for (e = instruction->eops; e; e = e->next) {
                osize = 0;
                if (e->type == EOT_DB_NUMBER) {
                    if (wsize == 1) {
                        if (e->segment != NO_SEG)
                            errfunc (ERR_NONFATAL,
                                     "one-byte relocation attempted");
                        else {
                            unsigned char c = e->offset;
                            outfmt->output (segment, &c, OUT_RAWDATA+1,
                                            NO_SEG, NO_SEG);
                        }
                    } else if (wsize > 5) {
                        errfunc (ERR_NONFATAL, "integer supplied to a D%c"
                                 " instruction", wsize==8 ? 'Q' : 'T');
                    } else
                        outfmt->output (segment, &e->offset,
                                        OUT_ADDRESS+wsize, e->segment,
                                        e->wrt);
                    offset += wsize;
                } else if (e->type == EOT_DB_STRING) {
                    int align;

                    align = (-e->stringlen) % wsize;
                    if (align < 0)
                        align += wsize;
                    outfmt->output (segment, e->stringval,
                                    OUT_RAWDATA+e->stringlen, NO_SEG, NO_SEG);
                    if (align)
                        outfmt->output (segment, "\0\0\0\0",
                                        OUT_RAWDATA+align, NO_SEG, NO_SEG);
                    offset += e->stringlen + align;
                }
            }
        }
        return offset - start;
    }

    size_prob = FALSE;
    temp = nasm_instructions[instruction->opcode];
    while (temp->opcode != -1) {
        int m = matches (temp, instruction);
        if (m == 100) {                /* matches! */
            char *codes = temp->code;
            long insn_size = calcsize(segment, offset, bits,
                                      instruction, codes);
            itimes = instruction->times;
            if (insn_size < 0)         /* shouldn't be, on pass two */
                error (ERR_PANIC, "errors made it through from pass one");
            else while (itimes--) {
                insn_end = offset + insn_size;
                for (j=0; j<instruction->nprefix; j++) {
                    unsigned char c;
                    switch (instruction->prefixes[j]) {
                      case P_LOCK:
                        c = 0xF0; break;
                      case P_REPNE: case P_REPNZ:
                        c = 0xF2; break;
                      case P_REPE: case P_REPZ: case P_REP:
                        c = 0xF3; break;
                      case R_CS: c = 0x2E; break;
                      case R_DS: c = 0x3E; break;
                      case R_ES: c = 0x26; break;
                      case R_FS: c = 0x64; break;
                      case R_GS: c = 0x65; break;
                      case R_SS: c = 0x36; break;
                      case P_A16:
                        if (bits == 16)
                            c = 0;     /* no prefix */
                        else
                            c = 0x67;
                        break;
                      case P_A32:
                        if (bits == 32)
                            c = 0;     /* no prefix */
                        else
                            c = 0x67;
                        break;
                      case P_O16:
                        if (bits == 16)
                            c = 0;     /* no prefix */
                        else
                            c = 0x66;
                        break;
                      case P_O32:
                        if (bits == 32)
                            c = 0;     /* no prefix */
                        else
                            c = 0x66;
                        break;
                      default:
                        error (ERR_PANIC,
                               "invalid instruction prefix");
                    }
                    if (c != 0)
                        outfmt->output (segment, &c, OUT_RAWDATA+1,
                                        NO_SEG, NO_SEG);
                    offset++;
                }
                gencode (segment, offset, bits, instruction, codes, insn_end);
                offset += insn_size;
            }
            return offset - start;
        } else if (m > 0) {
            size_prob = m;
        }
        temp++;
    }
    if (temp->opcode == -1) {          /* didn't match any instruction */
        if (size_prob == 1)            /* would have matched, but for size */
            error (ERR_NONFATAL, "operation size not specified");
        else if (size_prob == 2)
            error (ERR_NONFATAL, "mismatch in operand sizes");
        else
            error (ERR_NONFATAL,
                   "invalid combination of opcode and operands");
    }
    return 0;
}

long insn_size (long segment, long offset, int bits,
                insn *instruction, efunc error) {
    struct itemplate *temp;

    errfunc = error;                   /* to pass to other functions */

    if (instruction->opcode == -1)
        return 0;

    if (instruction->opcode == I_DB ||
        instruction->opcode == I_DW ||
        instruction->opcode == I_DD ||
        instruction->opcode == I_DQ ||
        instruction->opcode == I_DT) {
        extop *e;
        long isize, osize, wsize = 0;  /* placate gcc */

        isize = 0;
        switch (instruction->opcode) {
          case I_DB: wsize = 1; break;
          case I_DW: wsize = 2; break;
          case I_DD: wsize = 4; break;
          case I_DQ: wsize = 8; break;
          case I_DT: wsize = 10; break;
        }

        for (e = instruction->eops; e; e = e->next) {
            long align;

            osize = 0;
            if (e->type == EOT_DB_NUMBER)
                osize = 1;
            else if (e->type == EOT_DB_STRING)
                osize = e->stringlen;

            align = (-osize) % wsize;
            if (align < 0)
                align += wsize;
            isize += osize + align;
        }
        return isize * instruction->times;
    }

    temp = nasm_instructions[instruction->opcode];
    while (temp->opcode != -1) {
        if (matches(temp, instruction) == 100) {
            /* we've matched an instruction. */
            long isize;
            char *codes = temp->code;
            int j;

            isize = calcsize(segment, offset, bits, instruction, codes);
            if (isize < 0)
                return -1;
            for (j = 0; j < instruction->nprefix; j++) {
                if ((instruction->prefixes[j] != P_A16 &&
                     instruction->prefixes[j] != P_O16 && bits==16) ||
                    (instruction->prefixes[j] != P_A32 &&
                     instruction->prefixes[j] != P_O32 && bits==32))
                    isize++;
            }
            return isize * instruction->times;
        }
        temp++;
    }
    return -1;                         /* didn't match any instruction */
}

static long calcsize (long segment, long offset, int bits,
                      insn *ins, char *codes) {
    long length = 0;
    unsigned char c;

    while (*codes) switch (c = *codes++) {
      case 01: case 02: case 03:
        codes += c, length += c; break;
      case 04: case 05: case 06: case 07:
        length++; break;
      case 010: case 011: case 012:
        codes++, length++; break;
      case 017:
        length++; break;
      case 014: case 015: case 016:
        length++; break;
      case 020: case 021: case 022:
        length++; break;
      case 024: case 025: case 026:
        length++; break;
      case 030: case 031: case 032:
        length += 2; break;
      case 034: case 035: case 036:
        length += ((ins->oprs[c-034].addr_size ?
                    ins->oprs[c-034].addr_size : bits) == 16 ? 2 : 4); break;
      case 037:
        length += 2; break;
      case 040: case 041: case 042:
        length += 4; break;
      case 050: case 051: case 052:
        length++; break;
      case 060: case 061: case 062:
        length += 2; break;
      case 064: case 065: case 066:
        length += ((ins->oprs[c-064].addr_size ?
                    ins->oprs[c-064].addr_size : bits) == 16 ? 2 : 4); break;
      case 070: case 071: case 072:
        length += 4; break;
      case 0300: case 0301: case 0302:
        length += chsize (&ins->oprs[c-0300], bits);
        break;
      case 0310:
        length += (bits==32);
        break;
      case 0311:
        length += (bits==16);
        break;
      case 0312:
        break;
      case 0320:
        length += (bits==32);
        break;
      case 0321:
        length += (bits==16);
        break;
      case 0322:
        break;
      case 0330:
        codes++, length++; break;
      case 0340: case 0341: case 0342:
        if (ins->oprs[0].segment != NO_SEG)
            errfunc (ERR_NONFATAL, "attempt to reserve non-constant"
                     " quantity of BSS space");
        else
            length += ins->oprs[0].offset << (c-0340);
        break;
      default:                         /* can't do it by 'case' statements */
        if (c>=0100 && c<=0277) {      /* it's an EA */
            ea ea_data;
            if (!process_ea (&ins->oprs[(c>>3)&7], &ea_data, bits, 0,
                             ins->forw_ref)) {
                errfunc (ERR_NONFATAL, "invalid effective address");
                return -1;
            } else
                length += ea_data.size;
        } else
            errfunc (ERR_PANIC, "internal instruction table corrupt"
                     ": instruction code 0x%02X given", c);
    }
    return length;
}

static void gencode (long segment, long offset, int bits,
                     insn *ins, char *codes, long insn_end) {
    static char condval[] = { /* conditional opcodes */
        0x7, 0x3, 0x2, 0x6, 0x2, 0x4, 0xF, 0xD, 0xC, 0xE, 0x6, 0x2,
        0x3, 0x7, 0x3, 0x5, 0xE, 0xC, 0xD, 0xF, 0x1, 0xB, 0x9, 0x5,
        0x0, 0xA, 0xA, 0xB, 0x8, 0x4
    };
    unsigned char c, bytes[4];
    long data, size;

    while (*codes) switch (c = *codes++) {
      case 01: case 02: case 03:
        outfmt->output (segment, codes, OUT_RAWDATA+c, NO_SEG, NO_SEG);
        codes += c;
        offset += c;
        break;
      case 04: case 06:
        switch (ins->oprs[0].basereg) {
          case R_CS: bytes[0] = 0x0E + (c == 0x04 ? 1 : 0); break;
          case R_DS: bytes[0] = 0x1E + (c == 0x04 ? 1 : 0); break;
          case R_ES: bytes[0] = 0x06 + (c == 0x04 ? 1 : 0); break;
          case R_SS: bytes[0] = 0x16 + (c == 0x04 ? 1 : 0); break;
          default:
            errfunc (ERR_PANIC, "bizarre 8086 segment register received");
        }
        outfmt->output (segment, bytes, OUT_RAWDATA+1, NO_SEG, NO_SEG);
        offset++;
        break;
      case 05: case 07:
        switch (ins->oprs[0].basereg) {
          case R_FS: bytes[0] = 0xA0 + (c == 0x05 ? 1 : 0); break;
          case R_GS: bytes[0] = 0xA8 + (c == 0x05 ? 1 : 0); break;
          default:
            errfunc (ERR_PANIC, "bizarre 386 segment register received");
        }
        outfmt->output (segment, bytes, OUT_RAWDATA+1, NO_SEG, NO_SEG);
        offset++;
        break;
      case 010: case 011: case 012:
        bytes[0] = *codes++ + regval(&ins->oprs[c-010]);
        outfmt->output (segment, bytes, OUT_RAWDATA+1, NO_SEG, NO_SEG);
        offset += 1;
        break;
      case 017:
        bytes[0] = 0;
        outfmt->output (segment, bytes, OUT_RAWDATA+1, NO_SEG, NO_SEG);
        offset += 1;
        break;
      case 014: case 015: case 016:
        if (ins->oprs[c-014].offset < -128 || ins->oprs[c-014].offset > 127)
            errfunc (ERR_WARNING, "signed byte value exceeds bounds");
        bytes[0] = ins->oprs[c-014].offset;
        outfmt->output (segment, bytes, OUT_RAWDATA+1, NO_SEG, NO_SEG);
        offset += 1;
        break;
      case 020: case 021: case 022:
        if (ins->oprs[c-020].offset < -128 || ins->oprs[c-020].offset > 255)
            errfunc (ERR_WARNING, "byte value exceeds bounds");
        bytes[0] = ins->oprs[c-020].offset;
        outfmt->output (segment, bytes, OUT_RAWDATA+1, NO_SEG, NO_SEG);
        offset += 1;
        break;
      case 024: case 025: case 026:
        if (ins->oprs[c-024].offset < 0 || ins->oprs[c-024].offset > 255)
            errfunc (ERR_WARNING, "unsigned byte value exceeds bounds");
        bytes[0] = ins->oprs[c-024].offset;
        outfmt->output (segment, bytes, OUT_RAWDATA+1, NO_SEG, NO_SEG);
        offset += 1;
        break;
      case 030: case 031: case 032:
        if (ins->oprs[c-030].segment == NO_SEG &&
            ins->oprs[c-030].wrt == NO_SEG &&
            (ins->oprs[c-030].offset < -32768 ||
            ins->oprs[c-030].offset > 65535))
            errfunc (ERR_WARNING, "word value exceeds bounds");
        data = ins->oprs[c-030].offset;
        outfmt->output (segment, &data, OUT_ADDRESS+2,
                        ins->oprs[c-030].segment, ins->oprs[c-030].wrt);
        offset += 2;
        break;
      case 034: case 035: case 036:
        data = ins->oprs[c-034].offset;
        size = ((ins->oprs[c-034].addr_size ?
                 ins->oprs[c-034].addr_size : bits) == 16 ? 2 : 4);
        if (size==16 && (data < -32768 || data > 65535))
            errfunc (ERR_WARNING, "word value exceeds bounds");
        outfmt->output (segment, &data, OUT_ADDRESS+size,
                        ins->oprs[c-034].segment, ins->oprs[c-034].wrt);
        offset += size;
        break;
      case 037:
        if (ins->oprs[0].segment == NO_SEG)
            errfunc (ERR_NONFATAL, "value referenced by FAR is not"
                     " relocatable");
        data = 0L;
        outfmt->output (segment, &data, OUT_ADDRESS+2,
                        outfmt->segbase(1+ins->oprs[0].segment),
                        ins->oprs[0].wrt);
        offset += 2;
        break;
      case 040: case 041: case 042:
        data = ins->oprs[c-040].offset;
        outfmt->output (segment, &data, OUT_ADDRESS+4,
                        ins->oprs[c-040].segment, ins->oprs[c-040].wrt);
        offset += 4;
        break;
      case 050: case 051: case 052:
        if (ins->oprs[c-050].segment != segment)
            errfunc (ERR_NONFATAL, "short relative jump outside segment");
        data = ins->oprs[c-050].offset - insn_end;
        if (data > 127 || data < -128)
            errfunc (ERR_NONFATAL, "short jump is out of range");
        bytes[0] = data;
        outfmt->output (segment, bytes, OUT_RAWDATA+1, NO_SEG, NO_SEG);
        offset += 1;
        break;
      case 060: case 061: case 062:
        if (ins->oprs[c-060].segment != segment) {
            data = ins->oprs[c-060].offset;
            outfmt->output (segment, &data, OUT_REL2ADR+insn_end-offset,
                            ins->oprs[c-060].segment, ins->oprs[c-060].wrt);
        } else {
            data = ins->oprs[c-060].offset - insn_end;
            outfmt->output (segment, &data, OUT_ADDRESS+2, NO_SEG, NO_SEG);
        }
        offset += 2;
        break;
      case 064: case 065: case 066:
        size = ((ins->oprs[c-064].addr_size ?
                 ins->oprs[c-064].addr_size : bits) == 16 ? 2 : 4);
        if (ins->oprs[c-064].segment != segment) {
            data = ins->oprs[c-064].offset;
            size = (bits == 16 ? OUT_REL2ADR : OUT_REL4ADR);
            outfmt->output (segment, &data, size+insn_end-offset,
                            ins->oprs[c-064].segment, ins->oprs[c-064].wrt);
            size = (bits == 16 ? 2 : 4);
        } else {
            data = ins->oprs[c-064].offset - insn_end;
            outfmt->output (segment, &data, OUT_ADDRESS+size, NO_SEG, NO_SEG);
        }
        offset += size;
        break;
      case 070: case 071: case 072:
        if (ins->oprs[c-070].segment != segment) {
            data = ins->oprs[c-070].offset;
            outfmt->output (segment, &data, OUT_REL4ADR+insn_end-offset,
                            ins->oprs[c-070].segment, ins->oprs[c-070].wrt);
        } else {
            data = ins->oprs[c-070].offset - insn_end;
            outfmt->output (segment, &data, OUT_ADDRESS+4, NO_SEG, NO_SEG);
        }
        offset += 4;
        break;
      case 0300: case 0301: case 0302:
        if (chsize (&ins->oprs[c-0300], bits)) {
            *bytes = 0x67;
            outfmt->output (segment, bytes, OUT_RAWDATA+1, NO_SEG, NO_SEG);
            offset += 1;
        } else
            offset += 0;
        break;
      case 0310:
        if (bits==32) {
            *bytes = 0x67;
            outfmt->output (segment, bytes, OUT_RAWDATA+1, NO_SEG, NO_SEG);
            offset += 1;
        } else
            offset += 0;
        break;
      case 0311:
        if (bits==16) {
            *bytes = 0x67;
            outfmt->output (segment, bytes, OUT_RAWDATA+1, NO_SEG, NO_SEG);
            offset += 1;
        } else
            offset += 0;
        break;
      case 0312:
        break;
      case 0320:
        if (bits==32) {
            *bytes = 0x66;
            outfmt->output (segment, bytes, OUT_RAWDATA+1, NO_SEG, NO_SEG);
            offset += 1;
        } else
            offset += 0;
        break;
      case 0321:
        if (bits==16) {
            *bytes = 0x66;
            outfmt->output (segment, bytes, OUT_RAWDATA+1, NO_SEG, NO_SEG);
            offset += 1;
        } else
            offset += 0;
        break;
      case 0322:
        break;
      case 0330:
        *bytes = *codes++ + condval[ins->condition];
        outfmt->output (segment, bytes, OUT_RAWDATA+1, NO_SEG, NO_SEG);
        offset += 1;
        break;
      case 0340: case 0341: case 0342:
        if (ins->oprs[0].segment != NO_SEG)
            errfunc (ERR_PANIC, "non-constant BSS size in pass two");
        else {
            long size = ins->oprs[0].offset << (c-0340);
            outfmt->output (segment, NULL, OUT_RESERVE+size, NO_SEG, NO_SEG);
            offset += size;
        }
        break;
      default:                         /* can't do it by 'case' statements */
        if (c>=0100 && c<=0277) {      /* it's an EA */
            ea ea_data;
            int rfield;
            unsigned char *p;
            long s;

            if (c<=0177)               /* pick rfield from operand b */
                rfield = regval (&ins->oprs[c&7]);
            else                       /* rfield is constant */
                rfield = c & 7;
            if (!process_ea (&ins->oprs[(c>>3)&7], &ea_data, bits, rfield,
                             ins->forw_ref))
                errfunc (ERR_NONFATAL, "invalid effective address");

            p = bytes;
            *p++ = ea_data.modrm;
            if (ea_data.sib_present)
                *p++ = ea_data.sib;
            /*
             * the cast in the next line is to placate MS C...
             */
            outfmt->output (segment, bytes, OUT_RAWDATA+(long)(p-bytes),
                            NO_SEG, NO_SEG);
            s = p-bytes;

            switch (ea_data.bytes) {
              case 0:
                break;
              case 1:
                *bytes = ins->oprs[(c>>3)&7].offset;
                outfmt->output (segment, bytes, OUT_RAWDATA+1,
                                NO_SEG, NO_SEG);
                s++;
                break;
              case 2:
              case 4:
                data = ins->oprs[(c>>3)&7].offset;
                outfmt->output (segment, &data, OUT_ADDRESS+ea_data.bytes,
                                ins->oprs[(c>>3)&7].segment,
                                ins->oprs[(c>>3)&7].wrt);
                s += ea_data.bytes;
                break;
            }
            offset += s;
        } else
            errfunc (ERR_PANIC, "internal instruction table corrupt"
                     ": instruction code 0x%02X given", c);
    }
}

static int regval (operand *o) {
    switch (o->basereg) {
      case R_EAX: case R_AX: case R_AL: case R_ES: case R_CR0: case R_DR0:
      case R_ST0: case R_MM0:
        return 0;
      case R_ECX: case R_CX: case R_CL: case R_CS: case R_DR1: case R_ST1:
      case R_MM1:
        return 1;
      case R_EDX: case R_DX: case R_DL: case R_SS: case R_CR2: case R_DR2:
      case R_ST2: case R_MM2:
        return 2;
      case R_EBX: case R_BX: case R_BL: case R_DS: case R_CR3: case R_DR3:
      case R_TR3: case R_ST3: case R_MM3:
        return 3;
      case R_ESP: case R_SP: case R_AH: case R_FS: case R_CR4: case R_TR4:
      case R_ST4: case R_MM4:
        return 4;
      case R_EBP: case R_BP: case R_CH: case R_GS: case R_TR5: case R_ST5:
      case R_MM5:
        return 5;
      case R_ESI: case R_SI: case R_DH: case R_DR6: case R_TR6: case R_ST6:
      case R_MM6:
        return 6;
      case R_EDI: case R_DI: case R_BH: case R_DR7: case R_TR7: case R_ST7:
      case R_MM7:
        return 7;
      default:                         /* panic */
        errfunc (ERR_PANIC, "invalid register operand given to regval()");
        return 0;
    }
}

static int matches (struct itemplate *itemp, insn *instruction) {
    int i, size, oprs, ret;

    ret = 100;

    /*
     * Check the opcode
     */
    if (itemp->opcode != instruction->opcode) return 0;

    /*
     * Count the operands
     */
    if (itemp->operands != instruction->operands) return 0;

    /*
     * Check that no spurious colons or TOs are present
     */
    for (i=0; i<itemp->operands; i++)
        if (instruction->oprs[i].type & ~itemp->opd[i] & (COLON|TO))
            return 0;

    /*
     * Check that the operand flags all match up
     */
    for (i=0; i<itemp->operands; i++)
        if (itemp->opd[i] & ~instruction->oprs[i].type ||
            ((itemp->opd[i] & SIZE_MASK) &&
             ((itemp->opd[i] ^ instruction->oprs[i].type) & SIZE_MASK))) {
            if ((itemp->opd[i] & ~instruction->oprs[i].type & NON_SIZE) ||
                (instruction->oprs[i].type & SIZE_MASK))
                return 0;
            else
                ret = 1;
        }

    /*
     * Check operand sizes
     */
    if (itemp->flags & IF_SB) {
        size = BITS8;
        oprs = itemp->operands;
    } else if (itemp->flags & IF_SD) {
        size = BITS32;
        oprs = itemp->operands;
    } else if (itemp->flags & (IF_SM | IF_SM2)) {
        oprs = (itemp->flags & IF_SM2 ? 2 : itemp->operands);
        size = 0;                      /* placate gcc */
        for (i=0; i<oprs; i++)
            if ( (size = itemp->opd[i] & SIZE_MASK) != 0)
                break;
    } else {
        size = 0;
        oprs = itemp->operands;
    }

    for (i=0; i<itemp->operands; i++)
        if (!(itemp->opd[i] & SIZE_MASK) &&
            (instruction->oprs[i].type & SIZE_MASK & ~size))
            ret = 2;

    return ret;
}

static ea *process_ea (operand *input, ea *output, int addrbits, int rfield,
                       int forw_ref) {
    if (!(REGISTER & ~input->type)) {  /* it's a single register */
        static int regs[] = {
            R_MM0, R_EAX, R_AX, R_AL, R_MM1, R_ECX, R_CX, R_CL,
            R_MM2, R_EDX, R_DX, R_DL, R_MM3, R_EBX, R_BX, R_BL,
            R_MM4, R_ESP, R_SP, R_AH, R_MM5, R_EBP, R_BP, R_CH,
            R_MM6, R_ESI, R_SI, R_DH, R_MM7, R_EDI, R_DI, R_BH
        };
        int i;

        for (i=0; i<elements(regs); i++)
            if (input->basereg == regs[i]) break;
        if (i<elements(regs)) {
            output->sib_present = FALSE;/* no SIB necessary */
            output->bytes = 0;         /* no offset necessary either */
            output->modrm = 0xC0 | (rfield << 3) | (i/4);
        } else
            return NULL;
    } else {                           /* it's a memory reference */
        if (input->basereg==-1 && (input->indexreg==-1 || input->scale==0)) {
            /* it's a pure offset */
            if (input->addr_size)
                addrbits = input->addr_size;
            output->sib_present = FALSE;
            output->bytes = (addrbits==32 ? 4 : 2);
            output->modrm = (addrbits==32 ? 5 : 6) | (rfield << 3);
        } else {                       /* it's an indirection */
            int i=input->indexreg, b=input->basereg, s=input->scale;
            long o=input->offset, seg=input->segment;

            if (s==0) i = -1;          /* make this easy, at least */

            if (i==R_EAX || i==R_EBX || i==R_ECX || i==R_EDX
                || i==R_EBP || i==R_ESP || i==R_ESI || i==R_EDI
                || b==R_EAX || b==R_EBX || b==R_ECX || b==R_EDX
                || b==R_EBP || b==R_ESP || b==R_ESI || b==R_EDI) {
                /* it must be a 32-bit memory reference. Firstly we have
                 * to check that all registers involved are type Exx. */
                if (i!=-1 && i!=R_EAX && i!=R_EBX && i!=R_ECX && i!=R_EDX
                    && i!=R_EBP && i!=R_ESP && i!=R_ESI && i!=R_EDI)
                    return NULL;
                if (b!=-1 && b!=R_EAX && b!=R_EBX && b!=R_ECX && b!=R_EDX
                    && b!=R_EBP && b!=R_ESP && b!=R_ESI && b!=R_EDI)
                    return NULL;

                /* While we're here, ensure the user didn't specify WORD. */
                if (input->addr_size == 16)
                    return NULL;

                /* now reorganise base/index */
                if (b==i)              /* convert EAX+2*EAX to 3*EAX */
                    b = -1, s++;
                if (b==-1 && s==1)     /* single register should be base */
                    b = i, i = -1;
                if (((s==2 && i!=R_ESP) || s==3 || s==5 || s==9) && b==-1)
                    b = i, s--;       /* convert 3*EAX to EAX+2*EAX */
                if (s==1 && i==R_ESP)  /* swap ESP into base if scale is 1 */
                    i = b, b = R_ESP;
                if (i==R_ESP || (s!=1 && s!=2 && s!=4 && s!=8 && i!=-1))
                    return NULL;      /* wrong, for various reasons */

                if (i==-1 && b!=R_ESP) {/* no SIB needed */
                    int mod, rm;
                    switch(b) {
                      case R_EAX: rm = 0; break;
                      case R_ECX: rm = 1; break;
                      case R_EDX: rm = 2; break;
                      case R_EBX: rm = 3; break;
                      case R_EBP: rm = 5; break;
                      case R_ESI: rm = 6; break;
                      case R_EDI: rm = 7; break;
                      case -1: rm = 5; break;
                      default:         /* should never happen */
                        return NULL;
                    }
                    if (b==-1 || (b!=R_EBP && o==0 &&
                                  seg==NO_SEG && !forw_ref))
                        mod = 0;
                    else if (o>=-128 && o<=127 && seg==NO_SEG && !forw_ref)
                        mod = 1;
                    else
                        mod = 2;

                    output->sib_present = FALSE;
                    output->bytes = (b==-1 || mod==2 ? 4 : mod);
                    output->modrm = (mod<<6) | (rfield<<3) | rm;
                } else {               /* we need a SIB */
                    int mod, scale, index, base;

                    switch (b) {
                      case R_EAX: base = 0; break;
                      case R_ECX: base = 1; break;
                      case R_EDX: base = 2; break;
                      case R_EBX: base = 3; break;
                      case R_ESP: base = 4; break;
                      case R_EBP: case -1: base = 5; break;
                      case R_ESI: base = 6; break;
                      case R_EDI: base = 7; break;
                      default:         /* then what the smeg is it? */
                        return NULL;  /* panic */
                    }

                    switch (i) {
                      case R_EAX: index = 0; break;
                      case R_ECX: index = 1; break;
                      case R_EDX: index = 2; break;
                      case R_EBX: index = 3; break;
                      case -1: index = 4; break;
                      case R_EBP: index = 5; break;
                      case R_ESI: index = 6; break;
                      case R_EDI: index = 7; break;
                      default:         /* then what the smeg is it? */
                        return NULL;  /* panic */
                    }

                    if (i==-1) s = 1;
                    switch (s) {
                      case 1: scale = 0; break;
                      case 2: scale = 1; break;
                      case 4: scale = 2; break;
                      case 8: scale = 3; break;
                      default:         /* then what the smeg is it? */
                        return NULL;  /* panic */
                    }

                    if (b==-1 || (b!=R_EBP && o==0 &&
                                  seg==NO_SEG && !forw_ref))
                        mod = 0;
                    else if (o>=-128 && o<=127 && seg==NO_SEG && !forw_ref)
                        mod = 1;
                    else
                        mod = 2;

                    output->sib_present = TRUE;
                    output->bytes = (b==-1 || mod==2 ? 4 : mod);
                    output->modrm = (mod<<6) | (rfield<<3) | 4;
                    output->sib = (scale<<6) | (index<<3) | base;
                }
            } else {                   /* it's 16-bit */
                int mod, rm;

                /* check all registers are BX, BP, SI or DI */
                if ((b!=-1 && b!=R_BP && b!=R_BX && b!=R_SI && b!=R_DI) ||
                    (i!=-1 && i!=R_BP && i!=R_BX && i!=R_SI && i!=R_DI))
                    return NULL;

                /* ensure the user didn't specify DWORD */
                if (input->addr_size == 32)
                    return NULL;

                if (s!=1 && i!=-1) return NULL;/* no can do, in 16-bit EA */
                if (b==-1 && i!=-1) b ^= i ^= b ^= i;   /* swap them round */
                if ((b==R_SI || b==R_DI) && i!=-1)
                    b ^= i ^= b ^= i; /* have BX/BP as base, SI/DI index */
                if (b==i) return NULL;/* shouldn't ever happen, in theory */
                if (i!=-1 && b!=-1 &&
                    (i==R_BP || i==R_BX || b==R_SI || b==R_DI))
                    return NULL;      /* invalid combinations */
                if (b==-1)             /* pure offset: handled above */
                    return NULL;      /* so if it gets to here, panic! */

                rm = -1;
                if (i!=-1)
                    switch (i*256 + b) {
                      case R_SI*256+R_BX: rm=0; break;
                      case R_DI*256+R_BX: rm=1; break;
                      case R_SI*256+R_BP: rm=2; break;
                      case R_DI*256+R_BP: rm=3; break;
                    }
                else
                    switch (b) {
                      case R_SI: rm=4; break;
                      case R_DI: rm=5; break;
                      case R_BP: rm=6; break;
                      case R_BX: rm=7; break;
                    }
                if (rm==-1)            /* can't happen, in theory */
                    return NULL;      /* so panic if it does */

                if (o==0 && seg==NO_SEG && !forw_ref && rm!=6)
                    mod = 0;
                else if (o>=-128 && o<=127 && seg==NO_SEG && !forw_ref)
                    mod = 1;
                else
                    mod = 2;

                output->sib_present = FALSE;  /* no SIB - it's 16-bit */
                output->bytes = mod;  /* bytes of offset needed */
                output->modrm = (mod<<6) | (rfield<<3) | rm;
            }
        }
    }
    output->size = 1 + output->sib_present + output->bytes;
    return output;
}

static int chsize (operand *input, int addrbits) {
    if (!(MEMORY & ~input->type)) {
        int i=input->indexreg, b=input->basereg;

        if (input->scale==0) i = -1;

        if (i == -1 && b == -1) /* pure offset */
            return (input->addr_size != 0 && input->addr_size != addrbits);

        if (i==R_EAX || i==R_EBX || i==R_ECX || i==R_EDX
            || i==R_EBP || i==R_ESP || i==R_ESI || i==R_EDI
            || b==R_EAX || b==R_EBX || b==R_ECX || b==R_EDX
            || b==R_EBP || b==R_ESP || b==R_ESI || b==R_EDI)
            return (addrbits==16);
        else
            return (addrbits==32);
    } else
        return 0;
}