NASM 0.91

[nasm/avx512.git] / outobj.c

/* outobj.c     output routines for the Netwide Assembler to produce
 *              Microsoft 16-bit .OBJ object files
 *
 * 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.
 */

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

#include "nasm.h"
#include "nasmlib.h"
#include "outform.h"

#ifdef OF_OBJ

static char obj_infile[FILENAME_MAX];
static int obj_uppercase;

static efunc error;
static ldfunc deflabel;
static FILE *ofp;
static long first_seg;
static int any_segs;

#define LEDATA_MAX 1024                /* maximum size of LEDATA record */
#define RECORD_MAX 1024                /* maximum size of _any_ record */
#define GROUP_MAX 256                  /* we won't _realistically_ have more
                                        * than this many segs in a group */
#define EXT_BLKSIZ 256                 /* block size for externals list */

static unsigned char record[RECORD_MAX], *recptr;

static struct Public {
    struct Public *next;
    char *name;
    long offset;
    long segment;                      /* only if it's far-absolute */
} *fpubhead, **fpubtail;

static struct External {
    struct External *next;
    char *name;
    long commonsize;
} *exthead, **exttail;

static int externals;

static struct ExtBack {
    struct ExtBack *next;
    int index[EXT_BLKSIZ];
} *ebhead, **ebtail;

static struct Segment {
    struct Segment *next;
    long index;                        /* the NASM segment id */
    long obj_index;                    /* the OBJ-file segment index */
    struct Group *grp;                 /* the group it belongs to */
    long currentpos;
    long align;                        /* can be SEG_ABS + absolute addr */
    enum {
        CMB_PRIVATE = 0,
        CMB_PUBLIC = 2,
        CMB_STACK = 5,
        CMB_COMMON = 6
    } combine;
    long use32;                        /* is this segment 32-bit? */
    struct Public *pubhead, **pubtail;
    char *name;
    char *segclass, *overlay;          /* `class' is a C++ keyword :-) */
} *seghead, **segtail, *obj_seg_needs_update;

static struct Group {
    struct Group *next;
    char *name;
    long index;                        /* NASM segment id */
    long obj_index;                    /* OBJ-file group index */
    long nentries;                     /* number of elements... */
    long nindices;                     /* ...and number of index elts... */
    union {
        long index;
        char *name;
    } segs[GROUP_MAX];                 /* ...in this */
} *grphead, **grptail, *obj_grp_needs_update;

static struct ObjData {
    struct ObjData *next;
    int nonempty;
    struct Segment *seg;
    long startpos;
    int letype, ftype;
    unsigned char ledata[LEDATA_MAX], *lptr;
    unsigned char fixupp[RECORD_MAX], *fptr;
} *datahead, *datacurr, **datatail;

static long obj_entry_seg, obj_entry_ofs;

enum RecordID {                        /* record ID codes */

    THEADR = 0x80,                     /* module header */
    COMENT = 0x88,                     /* comment record */

    LNAMES = 0x96,                     /* list of names */

    SEGDEF = 0x98,                     /* segment definition */
    GRPDEF = 0x9A,                     /* group definition */
    EXTDEF = 0x8C,                     /* external definition */
    PUBDEF = 0x90,                     /* public definition */
    COMDEF = 0xB0,                     /* common definition */

    LEDATA = 0xA0,                     /* logical enumerated data */
    FIXUPP = 0x9C,                     /* fixups (relocations) */

    MODEND = 0x8A                      /* module end */
};

extern struct ofmt of_obj;

static long obj_ledata_space(struct Segment *);
static int obj_fixup_free(struct Segment *);
static void obj_ledata_new(struct Segment *);
static void obj_ledata_commit(void);
static void obj_write_fixup (struct ObjData *, int, int, long, long, long);
static long obj_segment (char *, int, int *);
static void obj_write_file(void);
static unsigned char *obj_write_data(unsigned char *, unsigned char *, int);
static unsigned char *obj_write_byte(unsigned char *, int);
static unsigned char *obj_write_word(unsigned char *, int);
static unsigned char *obj_write_dword(unsigned char *, long);
static unsigned char *obj_write_rword(unsigned char *, int);
static unsigned char *obj_write_name(unsigned char *, char *);
static unsigned char *obj_write_index(unsigned char *, int);
static unsigned char *obj_write_value(unsigned char *, unsigned long);
static void obj_record(int, unsigned char *, unsigned char *);

static void obj_init (FILE *fp, efunc errfunc, ldfunc ldef) {
    ofp = fp;
    error = errfunc;
    deflabel = ldef;
    first_seg = seg_alloc();
    any_segs = FALSE;
    fpubhead = NULL;
    fpubtail = &fpubhead;
    exthead = NULL;
    exttail = &exthead;
    externals = 0;
    ebhead = NULL;
    ebtail = &ebhead;
    seghead = obj_seg_needs_update = NULL;
    segtail = &seghead;
    grphead = obj_grp_needs_update = NULL;
    grptail = &grphead;
    datahead = datacurr = NULL;
    datatail = &datahead;
    obj_entry_seg = NO_SEG;
    obj_uppercase = FALSE;
}

static void obj_cleanup (void) {
    obj_write_file();
    fclose (ofp);
    while (seghead) {
        struct Segment *segtmp = seghead;
        seghead = seghead->next;
        while (segtmp->pubhead) {
            struct Public *pubtmp = segtmp->pubhead;
            segtmp->pubhead = pubtmp->next;
            nasm_free (pubtmp);
        }
        nasm_free (segtmp);
    }
    while (fpubhead) {
        struct Public *pubtmp = fpubhead;
        fpubhead = fpubhead->next;
        nasm_free (pubtmp);
    }
    while (exthead) {
        struct External *exttmp = exthead;
        exthead = exthead->next;
        nasm_free (exttmp);
    }
    while (ebhead) {
        struct ExtBack *ebtmp = ebhead;
        ebhead = ebhead->next;
        nasm_free (ebtmp);
    }
    while (grphead) {
        struct Group *grptmp = grphead;
        grphead = grphead->next;
        nasm_free (grptmp);
    }
    while (datahead) {
        struct ObjData *datatmp = datahead;
        datahead = datahead->next;
        nasm_free (datatmp);
    }
}

static void obj_deflabel (char *name, long segment,
                          long offset, int is_global) {
    /*
     * We have three cases:
     *
     * (i) `segment' is a segment-base. If so, set the name field
     * for the segment or group structure it refers to, and then
     * return.
     *
     * (ii) `segment' is one of our segments, or a SEG_ABS segment.
     * Save the label position for later output of a PUBDEF record.
     * (Or a MODPUB, if we work out how.)
     *
     * (iii) `segment' is not one of our segments. Save the label
     * position for later output of an EXTDEF, and also store a
     * back-reference so that we can map later references to this
     * segment number to the external index.
     */
    struct External *ext;
    struct ExtBack *eb;
    struct Segment *seg;
    int i;

    /*
     * First check for the double-period, signifying something
     * unusual.
     */
    if (name[0] == '.' && name[1] == '.') {
        if (!strcmp(name, "..start")) {
            obj_entry_seg = segment;
            obj_entry_ofs = offset;
        }
        return;
    }

    /*
     * Case (i):
     */
    if (obj_seg_needs_update) {
        obj_seg_needs_update->name = name;
        return;
    } else if (obj_grp_needs_update) {
        obj_grp_needs_update->name = name;
        return;
    }
    if (segment < SEG_ABS && segment != NO_SEG && segment % 2)
        return;

    if (segment >= SEG_ABS) {
        /*
         * SEG_ABS subcase of (ii).
         */
        if (is_global) {
            struct Public *pub;

            pub = *fpubtail = nasm_malloc(sizeof(*pub));
            fpubtail = &pub->next;
            pub->next = NULL;
            pub->name = name;
            pub->offset = offset;
            pub->segment = segment & ~SEG_ABS;
        }
        return;
    }

    for (seg = seghead; seg; seg = seg->next)
        if (seg->index == segment) {
            /*
             * Case (ii). Maybe MODPUB someday?
             */
            if (is_global) {
                struct Public *pub;

                pub = *seg->pubtail = nasm_malloc(sizeof(*pub));
                seg->pubtail = &pub->next;
                pub->next = NULL;
                pub->name = name;
                pub->offset = offset;
            }
            return;
        }

    /*
     * Case (iii).
     */
    ext = *exttail = nasm_malloc(sizeof(*ext));
    ext->next = NULL;
    exttail = &ext->next;
    ext->name = name;
    if (is_global == 2)
        ext->commonsize = offset;
    else
        ext->commonsize = 0;

    i = segment/2;
    eb = ebhead;
    if (!eb) {
        eb = *ebtail = nasm_malloc(sizeof(*eb));
        eb->next = NULL;
        ebtail = &eb->next;
    }
    while (i > EXT_BLKSIZ) {
        if (eb && eb->next)
            eb = eb->next;
        else {
            eb = *ebtail = nasm_malloc(sizeof(*eb));
            eb->next = NULL;
            ebtail = &eb->next;
        }
        i -= EXT_BLKSIZ;
    }
    eb->index[i] = ++externals;
}

static void obj_out (long segto, void *data, unsigned long type,
                     long segment, long wrt) {
    long size, realtype;
    unsigned char *ucdata;
    long ldata;
    struct Segment *seg;

    /*
     * handle absolute-assembly (structure definitions)
     */
    if (segto == NO_SEG) {
        if ((type & OUT_TYPMASK) != OUT_RESERVE)
            error (ERR_NONFATAL, "attempt to assemble code in [ABSOLUTE]"
                   " space");
        return;
    }

    /*
     * If `any_segs' is still FALSE, we must define a default
     * segment.
     */
    if (!any_segs) {
        int tempint;                   /* ignored */
        if (segto != obj_segment("__NASMDEFSEG", 2, &tempint))
            error (ERR_PANIC, "strange segment conditions in OBJ driver");
    }

    /*
     * Find the segment we are targetting.
     */
    for (seg = seghead; seg; seg = seg->next)
        if (seg->index == segto)
            break;
    if (!seg)
        error (ERR_PANIC, "code directed to nonexistent segment?");

    size = type & OUT_SIZMASK;
    realtype = type & OUT_TYPMASK;
    if (realtype == OUT_RAWDATA) {
        ucdata = data;
        while (size > 0) {
            long len = obj_ledata_space(seg);
            if (len == 0) {
                obj_ledata_new(seg);
                len = obj_ledata_space(seg);
            }
            if (len > size)
                len = size;
            datacurr->lptr = obj_write_data (datacurr->lptr, ucdata, len);
            datacurr->nonempty = TRUE;
            ucdata += len;
            size -= len;
            seg->currentpos += len;
        }
    } else if (realtype == OUT_ADDRESS || realtype == OUT_REL2ADR ||
               realtype == OUT_REL4ADR) {
        if (segment == NO_SEG && realtype != OUT_ADDRESS)
            error(ERR_NONFATAL, "relative call to absolute address not"
                  " supported by OBJ format");
        if (segment >= SEG_ABS)
            error(ERR_NONFATAL, "far-absolute relocations not supported"
                  " by OBJ format");
        ldata = *(long *)data;
        if (realtype == OUT_REL2ADR)
            ldata += (size-2);
        if (realtype == OUT_REL4ADR)
            ldata += (size-4);
        if (obj_ledata_space(seg) < 4 || !obj_fixup_free(seg))
            obj_ledata_new(seg);
        if (size == 2)
            datacurr->lptr = obj_write_word (datacurr->lptr, ldata);
        else
            datacurr->lptr = obj_write_dword (datacurr->lptr, ldata);
        datacurr->nonempty = TRUE;
        if (segment != NO_SEG)
            obj_write_fixup (datacurr, size,
                             (realtype == OUT_REL2ADR ? 0 : 0x4000),
                             segment, wrt,
                             (seg->currentpos - datacurr->startpos));
        seg->currentpos += size;
    } else if (realtype == OUT_RESERVE) {
        obj_ledata_commit();
        seg->currentpos += size;
    }
}

static long obj_ledata_space(struct Segment *segto) {
    if (datacurr && datacurr->seg == segto)
        return datacurr->ledata + LEDATA_MAX - datacurr->lptr;
    else
        return 0;
}

static int obj_fixup_free(struct Segment *segto) {
    if (datacurr && datacurr->seg == segto)
        return (datacurr->fixupp + RECORD_MAX - datacurr->fptr) > 8;
    else
        return 0;
}

static void obj_ledata_new(struct Segment *segto) {
    datacurr = *datatail = nasm_malloc(sizeof(*datacurr));
    datacurr->next = NULL;
    datatail = &datacurr->next;
    datacurr->nonempty = FALSE;
    datacurr->lptr = datacurr->ledata;
    datacurr->fptr = datacurr->fixupp;
    datacurr->seg = segto;
    if (segto->use32)
        datacurr->letype = LEDATA+1;
    else
        datacurr->letype = LEDATA;
    datacurr->startpos = segto->currentpos;
    datacurr->ftype = FIXUPP;

    datacurr->lptr = obj_write_index (datacurr->lptr, segto->obj_index);
    if (datacurr->letype == LEDATA)
        datacurr->lptr = obj_write_word (datacurr->lptr, segto->currentpos);
    else
        datacurr->lptr = obj_write_dword (datacurr->lptr, segto->currentpos);
}

static void obj_ledata_commit(void) {
    datacurr = NULL;
}

static void obj_write_fixup (struct ObjData *data, int bytes,
                             int segrel, long seg, long wrt,
                             long offset) {
    int locat, method;
    int base;
    long tidx, fidx;
    struct Segment *s = NULL;
    struct Group *g = NULL;

    locat = 0x8000 | segrel | offset;
    if (seg % 2) {
        base = TRUE;
        locat |= 0x800;
        seg--;
        if (bytes != 2)
            error(ERR_NONFATAL, "OBJ format can only handle 2-byte"
                  " segment base references");
    } else {
        base = FALSE;
        if (bytes == 2)
            locat |= 0x400;
        else {
            locat |= 0x2400;
            data->ftype = FIXUPP+1;    /* need new-style FIXUPP record */
        }
    }
    data->fptr = obj_write_rword (data->fptr, locat);

    tidx = fidx = -1, method = 0;      /* placate optimisers */

    /*
     * See if we can find the segment ID in our segment list. If
     * so, we have a T4 (LSEG) target.
     */
    for (s = seghead; s; s = s->next)
        if (s->index == seg)
            break;
    if (s)
        method = 4, tidx = s->obj_index;
    else {
        for (g = grphead; g; g = g->next)
            if (g->index == seg)
                break;
        if (g)
            method = 5, tidx = g->obj_index;
        else {
            long i = seg/2;
            struct ExtBack *eb = ebhead;
            while (i > EXT_BLKSIZ) {
                if (eb)
                    eb = eb->next;
                else
                    break;
                i -= EXT_BLKSIZ;
            }
            if (eb)
                method = 6, tidx = eb->index[i];
            else
                error(ERR_PANIC,
                      "unrecognised segment value in obj_write_fixup");
        }
    }

    /*
     * If no WRT given, assume the natural default, which is method
     * F5 unless we are doing an OFFSET fixup for a grouped
     * segment, in which case we require F1 (group).
     */
    if (wrt == NO_SEG) {
        if (!base && s && s->grp)
            method |= 0x10, fidx = s->grp->obj_index;
        else
            method |= 0x50, fidx = -1;
    } else {
        /*
         * See if we can find the WRT-segment ID in our segment
         * list. If so, we have a F0 (LSEG) frame.
         */
        for (s = seghead; s; s = s->next)
            if (s->index == wrt-1)
                break;
        if (s)
            method |= 0x00, fidx = s->obj_index;
        else {
            for (g = grphead; g; g = g->next)
                if (g->index == wrt-1)
                    break;
            if (g)
                method |= 0x10, fidx = g->obj_index;
            else {
                long i = wrt/2;
                struct ExtBack *eb = ebhead;
                while (i > EXT_BLKSIZ) {
                    if (eb)
                        eb = eb->next;
                    else
                        break;
                    i -= EXT_BLKSIZ;
                }
                if (eb)
                    method |= 0x20, fidx = eb->index[i];
                else
                    error(ERR_PANIC,
                          "unrecognised WRT value in obj_write_fixup");
            }
        }
    }

    data->fptr = obj_write_byte (data->fptr, method);
    if (fidx != -1)
        data->fptr = obj_write_index (data->fptr, fidx);
    data->fptr = obj_write_index (data->fptr, tidx);
}

static long obj_segment (char *name, int pass, int *bits) {
    /*
     * We call the label manager here to define a name for the new
     * segment, and when our _own_ label-definition stub gets
     * called in return, it should register the new segment name
     * using the pointer it gets passed. That way we save memory,
     * by sponging off the label manager.
     */
    if (!name) {
        *bits = 16;
        return first_seg;
    } else {
        struct Segment *seg;
        struct Group *grp;
        int obj_idx, i, attrs, rn_error;
        char *p;

        /*
         * Look for segment attributes.
         */
        attrs = 0;
        p = name;
        while (*p && !isspace(*p))
            p++;
        if (*p) {
            *p++ = '\0';
            while (*p && isspace(*p))
                *p++ = '\0';
        }
        while (*p) {
            while (*p && !isspace(*p))
                p++;
            if (*p) {
                *p++ = '\0';
                while (*p && isspace(*p))
                    *p++ = '\0';
            }

            attrs++;
        }

        obj_idx = 1;
        for (seg = seghead; seg; seg = seg->next) {
            obj_idx++;
            if (!strcmp(seg->name, name)) {
                if (attrs > 0 && pass == 1)
                    error(ERR_WARNING, "segment attributes specified on"
                          " redeclaration of segment: ignoring");
                if (seg->use32)
                    *bits = 32;
                else
                    *bits = 16;
                return seg->index;
            }
        }

        *segtail = seg = nasm_malloc(sizeof(*seg));
        seg->next = NULL;
        segtail = &seg->next;
        seg->index = (any_segs ? seg_alloc() : first_seg);
        seg->obj_index = obj_idx;
        seg->grp = NULL;
        any_segs = TRUE;
        seg->name = NULL;
        seg->currentpos = 0;
        seg->align = 1;                /* default */
        seg->use32 = FALSE;            /* default */
        seg->combine = CMB_PUBLIC;     /* default */
        seg->segclass = seg->overlay = NULL;
        seg->pubhead = NULL;
        seg->pubtail = &seg->pubhead;

        /*
         * Process the segment attributes.
         */
        p = name;
        while (attrs--) {
            p += strlen(p);
            while (!*p) p++;

            /*
             * `p' contains a segment attribute.
             */
            if (!nasm_stricmp(p, "private"))
                seg->combine = CMB_PRIVATE;
            else if (!nasm_stricmp(p, "public"))
                seg->combine = CMB_PUBLIC;
            else if (!nasm_stricmp(p, "common"))
                seg->combine = CMB_COMMON;
            else if (!nasm_stricmp(p, "stack"))
                seg->combine = CMB_STACK;
            else if (!nasm_stricmp(p, "use16"))
                seg->use32 = FALSE;
            else if (!nasm_stricmp(p, "use32"))
                seg->use32 = TRUE;
            else if (!nasm_strnicmp(p, "class=", 6))
                seg->segclass = nasm_strdup(p+6);
            else if (!nasm_strnicmp(p, "overlay=", 8))
                seg->overlay = nasm_strdup(p+8);
            else if (!nasm_strnicmp(p, "align=", 6)) {
                seg->align = readnum(p+6, &rn_error);
                if (rn_error) {
                    seg->align = 1;
                    error (ERR_NONFATAL, "segment alignment should be"
                           " numeric");
                }
                switch ((int) seg->align) {
                  case 1:              /* BYTE */
                  case 2:              /* WORD */
                  case 4:              /* DWORD */
                  case 16:             /* PARA */
                  case 256:            /* PAGE */
                    break;
                  case 8:
                    error(ERR_WARNING, "OBJ format does not support alignment"
                          " of 8: rounding up to 16");
                    seg->align = 16;
                    break;
                  case 32:
                  case 64:
                  case 128:
                    error(ERR_WARNING, "OBJ format does not support alignment"
                          " of %d: rounding up to 256", seg->align);
                    seg->align = 256;
                    break;
                  default:
                    error(ERR_NONFATAL, "invalid alignment value %d",
                          seg->align);
                    seg->align = 1;
                    break;
                }
            } else if (!nasm_strnicmp(p, "absolute=", 9)) {
                seg->align = SEG_ABS + readnum(p+9, &rn_error);
                if (rn_error)
                    error (ERR_NONFATAL, "argument to `absolute' segment"
                           " attribute should be numeric");
            }
        }

        obj_seg_needs_update = seg;
        if (seg->align >= SEG_ABS)
            deflabel (name, NO_SEG, seg->align - SEG_ABS, &of_obj, error);
        else
            deflabel (name, seg->index+1, 0L, &of_obj, error);
        obj_seg_needs_update = NULL;

        /*
         * See if this segment is defined in any groups.
         */
        for (grp = grphead; grp; grp = grp->next) {
            for (i = grp->nindices; i < grp->nentries; i++) {
                if (!strcmp(grp->segs[i].name, seg->name)) {
                    nasm_free (grp->segs[i].name);
                    grp->segs[i] = grp->segs[grp->nindices];
                    grp->segs[grp->nindices++].index = seg->obj_index;
                    if (seg->grp)
                        error(ERR_WARNING, "segment `%s' is already part of"
                              " a group: first one takes precedence",
                              seg->name);
                    else
                        seg->grp = grp;
                }
            }
        }

        if (seg->use32)
            *bits = 32;
        else
            *bits = 16;
        return seg->index;
    }
}

static int obj_directive (char *directive, char *value, int pass) {
    if (!strcmp(directive, "group")) {
        char *p, *q;
        if (pass == 1) {
            struct Group *grp;
            struct Segment *seg;
            int obj_idx;

            q = value;
            while (*q && !isspace(*q))
                q++;
            if (isspace(*q)) {
                *q++ = '\0';
                while (*q && isspace(*q))
                    q++;
            }
            if (!*q) {
                error(ERR_NONFATAL, "GROUP directive contains no segments");
                return 1;
            }

            obj_idx = 1;
            for (grp = grphead; grp; grp = grp->next) {
                obj_idx++;
                if (!strcmp(grp->name, value)) {
                    error(ERR_NONFATAL, "group `%s' defined twice", value);
                    return 1;
                }
            }

            *grptail = grp = nasm_malloc(sizeof(*grp));
            grp->next = NULL;
            grptail = &grp->next;
            grp->index = seg_alloc();
            grp->obj_index = obj_idx;
            grp->nindices = grp->nentries = 0;
            grp->name = NULL;

            obj_grp_needs_update = grp;
            deflabel (value, grp->index+1, 0L, &of_obj, error);
            obj_grp_needs_update = NULL;

            while (*q) {
                p = q;
                while (*q && !isspace(*q))
                    q++;
                if (isspace(*q)) {
                    *q++ = '\0';
                    while (*q && isspace(*q))
                        q++;
                }
                /*
                 * Now p contains a segment name. Find it.
                 */
                for (seg = seghead; seg; seg = seg->next)
                    if (!strcmp(seg->name, p))
                        break;
                if (seg) {
                    /*
                     * We have a segment index. Shift a name entry
                     * to the end of the array to make room.
                     */
                    grp->segs[grp->nentries++] = grp->segs[grp->nindices];
                    grp->segs[grp->nindices++].index = seg->obj_index;
                    if (seg->grp)
                        error(ERR_WARNING, "segment `%s' is already part of"
                              " a group: first one takes precedence",
                              seg->name);
                    else
                        seg->grp = grp;
                } else {
                    /*
                     * We have an as-yet undefined segment.
                     * Remember its name, for later.
                     */
                    grp->segs[grp->nentries++].name = nasm_strdup(p);
                }
            }
        }
        return 1;
    }
    if (!strcmp(directive, "uppercase")) {
        obj_uppercase = TRUE;
        return 1;
    }
    return 0;
}

static long obj_segbase (long segment) {
    struct Segment *seg;

    /*
     * Find the segment in our list.
     */
    for (seg = seghead; seg; seg = seg->next)
        if (seg->index == segment-1)
            break;

    if (!seg)
        return segment;                /* not one of ours - leave it alone */

    if (seg->align >= SEG_ABS)
        return seg->align;             /* absolute segment */
    if (seg->grp)
        return seg->grp->index+1;      /* grouped segment */

    return segment;                    /* no special treatment */
}

static void obj_filename (char *inname, char *outname, efunc error) {
    strcpy(obj_infile, inname);
    standard_extension (inname, outname, ".obj", error);
}

static void obj_write_file (void) {
    struct Segment *seg;
    struct Group *grp;
    struct Public *pub;
    struct External *ext;
    struct ObjData *data;
    static unsigned char boast[] = "The Netwide Assembler " NASM_VER;
    int lname_idx, rectype;

    /*
     * Write the THEADR module header.
     */
    recptr = record;
    recptr = obj_write_name (recptr, obj_infile);
    obj_record (THEADR, record, recptr);

    /*
     * Write the NASM boast comment.
     */
    recptr = record;
    recptr = obj_write_rword (recptr, 0);   /* comment type zero */
    recptr = obj_write_data (recptr, boast, sizeof(boast)-1);
    obj_record (COMENT, record, recptr);

    /*
     * Write the first LNAMES record, containing LNAME one, which
     * is null. Also initialise the LNAME counter.
     */
    recptr = record;
    recptr = obj_write_name (recptr, "");
    obj_record (LNAMES, record, recptr);
    lname_idx = 2;

    /*
     * Write the SEGDEF records. Each has an associated LNAMES
     * record.
     */
    for (seg = seghead; seg; seg = seg->next) {
        int new_segdef;                /* do we use the newer record type? */
        int acbp;
        int sn, cn, on;                /* seg, class, overlay LNAME idx */

        if (seg->use32 || seg->currentpos >= 0x10000)
            new_segdef = TRUE;
        else
            new_segdef = FALSE;

        recptr = record;
        recptr = obj_write_name (recptr, seg->name);
        sn = lname_idx++;
        if (seg->segclass) {
            recptr = obj_write_name (recptr, seg->segclass);
            cn = lname_idx++;
        } else
            cn = 1;
        if (seg->overlay) {
            recptr = obj_write_name (recptr, seg->overlay);
            on = lname_idx++;
        } else
            on = 1;
        obj_record (LNAMES, record, recptr);

        acbp = (seg->combine << 2);    /* C field */

        if (seg->currentpos >= 0x10000 && !new_segdef)
            acbp |= 0x02;              /* B bit */

        if (seg->use32)
            acbp |= 0x01;              /* P bit is Use32 flag */

        /* A field */
        if (seg->align >= SEG_ABS)
            acbp |= 0x00;
        else if (seg->align >= 256) {
            if (seg->align > 256)
                error(ERR_NONFATAL, "segment `%s' requires more alignment"
                      " than OBJ format supports", seg->name);
            acbp |= 0x80;
        } else if (seg->align >= 16) {
            acbp |= 0x60;
        } else if (seg->align >= 4) {
            acbp |= 0xA0;
        } else if (seg->align >= 2) {
            acbp |= 0x40;
        } else
            acbp |= 0x20;

        recptr = record;
        recptr = obj_write_byte (recptr, acbp);
        if (seg->align & SEG_ABS) {
            recptr = obj_write_word (recptr, seg->align - SEG_ABS);
            recptr = obj_write_byte (recptr, 0);
        }
        if (new_segdef)
            recptr = obj_write_dword (recptr, seg->currentpos);
        else
            recptr = obj_write_word (recptr, seg->currentpos & 0xFFFF);
        recptr = obj_write_index (recptr, sn);
        recptr = obj_write_index (recptr, cn);
        recptr = obj_write_index (recptr, on);
        if (new_segdef)
            obj_record (SEGDEF+1, record, recptr);
        else
            obj_record (SEGDEF, record, recptr);
    }

    /*
     * Write some LNAMES for the group names. lname_idx is left
     * alone here - it will catch up when we write the GRPDEFs.
     */
    recptr = record;
    for (grp = grphead; grp; grp = grp->next) {
        recptr = obj_write_name (recptr, grp->name);
        if (recptr - record > 1024) {
            obj_record (LNAMES, record, recptr);
            recptr = record;
        }
    }
    if (recptr > record)
        obj_record (LNAMES, record, recptr);

    /*
     * Write the GRPDEF records.
     */
    for (grp = grphead; grp; grp = grp->next) {
        int i;

        if (grp->nindices != grp->nentries) {
            for (i = grp->nindices; i < grp->nentries; i++) {
                error(ERR_NONFATAL, "group `%s' contains undefined segment"
                      " `%s'", grp->name, grp->segs[i].name);
                nasm_free (grp->segs[i].name);
                grp->segs[i].name = NULL;
            }
        }
        recptr = record;
        recptr = obj_write_index (recptr, lname_idx++);
        for (i = 0; i < grp->nindices; i++) {
            recptr = obj_write_byte (recptr, 0xFF);
            recptr = obj_write_index (recptr, grp->segs[i].index);
        }
        obj_record (GRPDEF, record, recptr);
    }

    /*
     * Write the PUBDEF records: first the ones in the segments,
     * then the far-absolutes.
     */
    for (seg = seghead; seg; seg = seg->next) {
        int any;

        recptr = record;
        recptr = obj_write_index (recptr, seg->grp ? seg->grp->obj_index : 0);
        recptr = obj_write_index (recptr, seg->obj_index);
        any = FALSE;
        if (seg->use32)
            rectype = PUBDEF+1;
        else
            rectype = PUBDEF;
        for (pub = seg->pubhead; pub; pub = pub->next) {
            if (recptr - record + strlen(pub->name) > 1024) {
                if (any)
                    obj_record (rectype, record, recptr);
                recptr = record;
                recptr = obj_write_index (recptr, 0);
                recptr = obj_write_index (recptr, seg->obj_index);
            }
            recptr = obj_write_name (recptr, pub->name);
            if (seg->use32)
                recptr = obj_write_dword (recptr, pub->offset);
            else
                recptr = obj_write_word (recptr, pub->offset);
            recptr = obj_write_index (recptr, 0);
            any = TRUE;
        }
        if (any)
            obj_record (rectype, record, recptr);
    }
    for (pub = fpubhead; pub; pub = pub->next) {   /* pub-crawl :-) */
        recptr = record;
        recptr = obj_write_index (recptr, 0);   /* no group */
        recptr = obj_write_index (recptr, 0);   /* no segment either */
        recptr = obj_write_word (recptr, pub->segment);
        recptr = obj_write_name (recptr, pub->name);
        recptr = obj_write_word (recptr, pub->offset);
        recptr = obj_write_index (recptr, 0);
        obj_record (PUBDEF, record, recptr);
    }

    /*
     * Write the EXTDEF and COMDEF records, in order.
     */
    recptr = record;
    for (ext = exthead; ext; ext = ext->next) {
        if (ext->commonsize == 0) {
            recptr = obj_write_name (recptr, ext->name);
            recptr = obj_write_index (recptr, 0);
            if (recptr - record > 1024) {
                obj_record (EXTDEF, record, recptr);
                recptr = record;
            }
        } else {
            if (recptr > record)
                obj_record (EXTDEF, record, recptr);
            recptr = record;
            if (ext->commonsize > 0) {
                recptr = obj_write_name (recptr, ext->name);
                recptr = obj_write_index (recptr, 0);
                recptr = obj_write_byte (recptr, 0x61);/* far communal */
                recptr = obj_write_value (recptr, 1L);
                recptr = obj_write_value (recptr, ext->commonsize);
                obj_record (COMDEF, record, recptr);
            } else if (ext->commonsize < 0) {
                recptr = obj_write_name (recptr, ext->name);
                recptr = obj_write_index (recptr, 0);
                recptr = obj_write_byte (recptr, 0x62);/* near communal */
                recptr = obj_write_value (recptr, ext->commonsize);
                obj_record (COMDEF, record, recptr);
            }
            recptr = record;
        }
    }
    if (recptr > record)
        obj_record (EXTDEF, record, recptr);

    /*
     * Write a COMENT record stating that the linker's first pass
     * may stop processing at this point.
     */
    recptr = record;
    recptr = obj_write_rword (recptr, 0x40A2);
    recptr = obj_write_byte (recptr, 1);
    obj_record (COMENT, record, recptr);

    /*
     * Write the LEDATA/FIXUPP pairs.
     */
    for (data = datahead; data; data = data->next) {
        if (data->nonempty) {
            obj_record (data->letype, data->ledata, data->lptr);
            if (data->fptr != data->fixupp)
                obj_record (FIXUPP, data->fixupp, data->fptr);
        }
    }

    /*
     * Write the MODEND module end marker.
     */
    recptr = record;
    rectype = MODEND;
    if (obj_entry_seg != NO_SEG) {
        recptr = obj_write_byte (recptr, 0xC1);
        /*
         * Find the segment in the segment list.
         */
        for (seg = seghead; seg; seg = seg->next) {
            if (seg->index == obj_entry_seg) {
                if (seg->grp) {
                    recptr = obj_write_byte (recptr, 0x10);
                    recptr = obj_write_index (recptr, seg->grp->obj_index);
                } else {
                    recptr = obj_write_byte (recptr, 0x50);
                }
                recptr = obj_write_index (recptr, seg->obj_index);
                if (seg->use32) {
                    rectype = MODEND+1;
                    recptr = obj_write_dword (recptr, obj_entry_ofs);
                } else
                    recptr = obj_write_word (recptr, obj_entry_ofs);
                break;
            }
        }
        if (!seg)
            error(ERR_NONFATAL, "entry point is not in this module");
    } else
        recptr = obj_write_byte (recptr, 0);
    obj_record (rectype, record, recptr);
}

static unsigned char *obj_write_data(unsigned char *ptr,
                                     unsigned char *data, int len) {
    while (len--)
        *ptr++ = *data++;
    return ptr;
}

static unsigned char *obj_write_byte(unsigned char *ptr, int data) {
    *ptr++ = data;
    return ptr;
}

static unsigned char *obj_write_word(unsigned char *ptr, int data) {
    *ptr++ = data & 0xFF;
    *ptr++ = (data >> 8) & 0xFF;
    return ptr;
}

static unsigned char *obj_write_dword(unsigned char *ptr, long data) {
    *ptr++ = data & 0xFF;
    *ptr++ = (data >> 8) & 0xFF;
    *ptr++ = (data >> 16) & 0xFF;
    *ptr++ = (data >> 24) & 0xFF;
    return ptr;
}

static unsigned char *obj_write_rword(unsigned char *ptr, int data) {
    *ptr++ = (data >> 8) & 0xFF;
    *ptr++ = data & 0xFF;
    return ptr;
}

static unsigned char *obj_write_name(unsigned char *ptr, char *data) {
    *ptr++ = strlen(data);
    if (obj_uppercase) {
        while (*data) {
            *ptr++ = (unsigned char) toupper(*data);
            data++;
        }
    } else {
        while (*data)
            *ptr++ = (unsigned char) *data++;
    }
    return ptr;
}

static unsigned char *obj_write_index(unsigned char *ptr, int data) {
    if (data < 128)
        *ptr++ = data;
    else {
        *ptr++ = 0x80 | ((data >> 8) & 0x7F);
        *ptr++ = data & 0xFF;
    }
    return ptr;
}

static unsigned char *obj_write_value(unsigned char *ptr,
                                      unsigned long data) {
    if (data <= 128)
        *ptr++ = data;
    else if (data <= 0xFFFF) {
        *ptr++ = 129;
        *ptr++ = data & 0xFF;
        *ptr++ = (data >> 8) & 0xFF;
    } else if (data <= 0xFFFFFF) {
        *ptr++ = 132;
        *ptr++ = data & 0xFF;
        *ptr++ = (data >> 8) & 0xFF;
        *ptr++ = (data >> 16) & 0xFF;
    } else {
        *ptr++ = 136;
        *ptr++ = data & 0xFF;
        *ptr++ = (data >> 8) & 0xFF;
        *ptr++ = (data >> 16) & 0xFF;
        *ptr++ = (data >> 24) & 0xFF;
    }
    return ptr;
}

static void obj_record(int type, unsigned char *start, unsigned char *end) {
    unsigned long cksum, len;

    cksum = type;
    fputc (type, ofp);
    len = end-start+1;
    cksum += (len & 0xFF) + ((len>>8) & 0xFF);
    fwriteshort (len, ofp);
    fwrite (start, 1, end-start, ofp);
    while (start < end)
        cksum += *start++;
    fputc ( (-cksum) & 0xFF, ofp);
}

struct ofmt of_obj = {
    "Microsoft MS-DOS 16-bit object files",
    "obj",
    obj_init,
    obj_out,
    obj_deflabel,
    obj_segment,
    obj_segbase,
    obj_directive,
    obj_filename,
    obj_cleanup
};

#endif /* OF_OBJ */