doslang-mirror/fec/src/x86.c

#include "x86.h"
#include <string.h>
#include <stdlib.h>

/* ------------------------------------------------------------------------- *
 * i386 code generation
 *
 * The frame, from EBP downwards:
 *
 *     [ebp + 8 + 4k]   incoming argument k
 *     [ebp + 4]        return address
 *     [ebp]            saved ebp
 *     [ebp - ...]      parameters, copied in from the argument area
 *     [ebp - ...]      locals
 *     [ebp - ...]      one slot per temporary
 *
 * Parameters are copied into the frame rather than read in place so that a
 * parameter and a local are the same thing to everything below.
 * ------------------------------------------------------------------------- */

/* Which register a temporary lives in, or none. Only ebx, esi and edi are
   handed out: eax, ecx and edx are the scratch this emitter computes in, and
   the three that are left survive a call without being saved. */
#define REG_NONE 0
#define REG_COUNT 3
static const char *const REGS[REG_COUNT] = { "ebx", "esi", "edi" };

typedef struct Frame {
    const FeIrFunc *f;
    long *local_off;         /* [ebp + off] for each local */
    long temp_base;          /* first temporary slot */
    long size;               /* bytes to subtract from esp */
    /* 0 means the temporary lives in its stack slot. */
    unsigned char *temp_reg;
} Frame;

static long align_up(long v, long a)
{
    long r = v % a;
    return r ? v + a - r : v;
}

static unsigned long slot_bytes(const FeIrLocal *l)
{
    switch (l->type) {
    case FE_IR_I8:  return 1;
    case FE_IR_I16: return 2;
    case FE_IR_I32: return 4;
    case FE_IR_PTR: return 4;
    case FE_IR_MEM: return l->size ? l->size : 1;
    default:        return 4;
    }
}

/* Every temporary is four bytes: a temporary only ever holds something that
   fits in a register, and narrower values are kept zero- or sign-extended. */
#define TEMP_SLOT 4L

static void frame_layout(Frame *fr, const FeIrFunc *f, long *storage)
{
    unsigned i;
    long off = 0;
    fr->f = f;
    fr->local_off = storage;
    for (i = 0; i < f->local_count; ++i) {
        unsigned long size = slot_bytes(&f->locals[i]);
        long a = (long)f->locals[i].align;
        if (a < 1) a = 1;
        if (a > 4) a = 4;
        off = align_up(off + (long)size, a);
        storage[i] = -off;
    }
    off = align_up(off, 4);
    fr->temp_base = -off;
    off += (long)f->temp_count * TEMP_SLOT;
    fr->size = align_up(off, 4);
}

/* Which temporaries a value reads. Returns how many it wrote into `used`. */
static unsigned reads_of(const FeIrValue *v, unsigned *used)
{
    unsigned n = 0;
    unsigned i;
    switch (v->op) {
    case FE_IR_CONST: break;
    case FE_IR_LOAD:
    case FE_IR_ADDR:
        if (v->place.base == FE_PLACE_TEMP) used[n++] = v->place.index;
        break;
    case FE_IR_STORE:
        if (v->place.base == FE_PLACE_TEMP) used[n++] = v->place.index;
        used[n++] = v->a;
        break;
    case FE_IR_COPY:
        if (v->place.base == FE_PLACE_TEMP) used[n++] = v->place.index;
        if (v->place2.base == FE_PLACE_TEMP) used[n++] = v->place2.index;
        break;
    case FE_IR_CAST:
        used[n++] = v->a;
        break;
    case FE_IR_CALL:
        for (i = 0; i < v->arg_count && n < 18; ++i) used[n++] = v->args[i];
        break;
    default:
        used[n++] = v->a;
        used[n++] = v->b;
        break;
    }
    return n;
}

/* Give registers to the temporaries that can hold one.

   A temporary that is defined in one block and read in another has to go
   through memory: this walks one block at a time and knows nothing about the
   others. Lowering does produce such temporaries -- a bounds check splits a
   block between computing an index and using it -- so eligibility is decided
   over the whole function first, and the scan inside a block only considers
   what survived that. */
static void allocate_registers(Frame *fr, const FeIrFunc *f)
{
    unsigned n = f->temp_count;
    unsigned char *single;      /* 1 while the temporary stays in one block */
    unsigned *home;             /* the block it was defined in */
    unsigned *last;             /* the last instruction in that block to read it */
    const FeIrBlock *b;
    const FeIrValue *v;
    unsigned used[20];
    unsigned i, k, at;
    if (!n) { fr->temp_reg = 0; return; }
    fr->temp_reg = (unsigned char *)calloc(n, 1);
    single = (unsigned char *)calloc(n, 1);
    home = (unsigned *)calloc(n, sizeof(unsigned));
    last = (unsigned *)calloc(n, sizeof(unsigned));
    if (!fr->temp_reg || !single || !home || !last) {
        free(single); free(home); free(last);
        return;
    }
    for (i = 0; i < n; ++i) { single[i] = 1; home[i] = 0xFFFFFFFFU; }
    for (b = f->first; b; b = b->next) {
        for (v = b->first; v; v = v->next) {
            if (v->has_dest) {
                if (home[v->dest] != 0xFFFFFFFFU) single[v->dest] = 0;
                home[v->dest] = b->id;
            }
            k = reads_of(v, used);
            for (i = 0; i < k; ++i)
                if (used[i] < n && home[used[i]] != b->id) single[used[i]] = 0;
        }
        if (b->term == FE_IR_BR && b->cond < n && home[b->cond] != b->id)
            single[b->cond] = 0;
        if (b->term == FE_IR_RET && b->has_ret_value && b->ret_value < n &&
            home[b->ret_value] != b->id)
            single[b->ret_value] = 0;
    }

    for (b = f->first; b; b = b->next) {
        unsigned char busy[REG_COUNT];
        unsigned owner[REG_COUNT];
        for (i = 0; i < REG_COUNT; ++i) { busy[i] = 0; owner[i] = 0; }
        /* When each temporary is last read in this block. */
        at = 0;
        for (v = b->first; v; v = v->next, ++at) {
            k = reads_of(v, used);
            for (i = 0; i < k; ++i)
                if (used[i] < n && single[used[i]]) last[used[i]] = at;
        }
        if (b->term == FE_IR_BR && b->cond < n && single[b->cond])
            last[b->cond] = at;
        if (b->term == FE_IR_RET && b->has_ret_value && b->ret_value < n &&
            single[b->ret_value]) last[b->ret_value] = at;

        at = 0;
        for (v = b->first; v; v = v->next, ++at) {
            /* Free whatever was read for the last time before this. */
            for (i = 0; i < REG_COUNT; ++i)
                if (busy[i] && last[owner[i]] < at) busy[i] = 0;
            if (!v->has_dest || !single[v->dest]) continue;
            /* A call clobbers the scratch registers but not these three, so a
               result can still be kept in one across the call that made it. */
            for (i = 0; i < REG_COUNT; ++i)
                if (!busy[i]) {
                    busy[i] = 1;
                    owner[i] = v->dest;
                    fr->temp_reg[v->dest] = (unsigned char)(i + 1);
                    break;
                }
        }
    }
    free(single); free(home); free(last);
}

static long temp_off(const Frame *fr, unsigned t)
{
    return fr->temp_base - (long)(t + 1) * TEMP_SLOT;
}

static const char *word_of(FeIrType t)
{
    switch (t) {
    case FE_IR_I8:  return "byte ptr";
    case FE_IR_I16: return "word ptr";
    default:        return "dword ptr";
    }
}

static const char *reg_of(FeIrType t, int which)
{
    /* which: 0 -> a, 1 -> c, 2 -> d */
    switch (t) {
    case FE_IR_I8:  return which == 0 ? "al" : which == 1 ? "cl" : "dl";
    case FE_IR_I16: return which == 0 ? "ax" : which == 1 ? "cx" : "dx";
    default:        return which == 0 ? "eax" : which == 1 ? "ecx" : "edx";
    }
}

/* Write the effective address of a place into `buf`. A place is a base plus a
   constant, and the only base that is not already an address is a temporary,
   which holds a pointer. */
static void place_addr(const Frame *fr, const FeIrPlace *p, char *buf)
{
    switch (p->base) {
    case FE_PLACE_LOCAL:
        sprintf(buf, "[ebp%+ld]", fr->local_off[p->index] + p->offset);
        break;
    case FE_PLACE_GLOBAL:
        if (p->offset) sprintf(buf, "[%s%+ld]", p->name, p->offset);
        else sprintf(buf, "[%s]", p->name);
        break;
    case FE_PLACE_TEMP:
        sprintf(buf, "[edx%+ld]", p->offset);
        break;
    }
}

/* A temporary-based place needs its pointer in a register first. */
static void load_temp(const Frame *fr, unsigned t, const char *reg,
                      FILE *out);

static void load_place_base(const Frame *fr, const FeIrPlace *p, FILE *out)
{
    if (p->base != FE_PLACE_TEMP) return;
    /* Through load_temp, not straight from the slot: the pointer may be living
       in a register, in which case the slot was never written. */
    load_temp(fr, p->index, "edx", out);
}

static void load_temp(const Frame *fr, unsigned t, const char *reg, FILE *out)
{
    if (fr->temp_reg && fr->temp_reg[t]) {
        const char *from = REGS[fr->temp_reg[t] - 1];
        if (strcmp(from, reg) != 0)
            fprintf(out, "        mov     %s, %s\n", reg, from);
        return;
    }
    fprintf(out, "        mov     %s, [ebp%+ld]\n", reg, temp_off(fr, t));
}

static void store_temp(const Frame *fr, unsigned t, const char *reg, FILE *out)
{
    if (fr->temp_reg && fr->temp_reg[t]) {
        const char *to = REGS[fr->temp_reg[t] - 1];
        if (strcmp(to, reg) != 0)
            fprintf(out, "        mov     %s, %s\n", to, reg);
        return;
    }
    fprintf(out, "        mov     [ebp%+ld], %s\n", temp_off(fr, t), reg);
}

/* The register a temporary lives in, or null when it lives in its slot. */
static const char *reg_home(const Frame *fr, unsigned t)
{
    if (!fr->temp_reg || !fr->temp_reg[t]) return 0;
    return REGS[fr->temp_reg[t] - 1];
}

/* Something an instruction can take as its right-hand operand: a register, or
   the temporary's slot read in place. */
static void operand_of(const Frame *fr, unsigned t, char *buf)
{
    const char *r = reg_home(fr, t);
    if (r) strcpy(buf, r);
    else sprintf(buf, "dword ptr [ebp%+ld]", temp_off(fr, t));
}

static const char *simple_op(FeIrOp op)
{
    switch (op) {
    case FE_IR_ADD: return "add ";
    case FE_IR_SUB: return "sub ";
    case FE_IR_AND: return "and ";
    case FE_IR_OR:  return "or  ";
    case FE_IR_XOR: return "xor ";
    case FE_IR_MUL: return "imul";
    default:        return 0;
    }
}

static const char *cmp_set(FeIrOp op, int is_unsigned)
{
    switch (op) {
    case FE_IR_EQ: return "sete";
    case FE_IR_NE: return "setne";
    case FE_IR_LT: return is_unsigned ? "setb"  : "setl";
    case FE_IR_LE: return is_unsigned ? "setbe" : "setle";
    case FE_IR_GT: return is_unsigned ? "seta"  : "setg";
    case FE_IR_GE: return is_unsigned ? "setae" : "setge";
    default:       return "sete";
    }
}

static void emit_binary(const Frame *fr, const FeIrValue *v, FILE *out)
{
    int is_cmp = v->op >= FE_IR_EQ && v->op <= FE_IR_GE;
    FeIrType t = is_cmp ? (FeIrType)v->imm : v->type;
    const char *a = reg_of(t, 0);
    const char *c = reg_of(t, 1);
    /* When the result has a register of its own and the operation is one that
       can work on any register, the whole thing happens there: no trip through
       the scratch register and no trip through memory.

       Only the full-width operations qualify. esi and edi have no byte halves,
       so a narrow operation still goes through eax, where they do. */
    if (!is_cmp && v->has_dest && (t == FE_IR_I32 || t == FE_IR_PTR) &&
        simple_op(v->op)) {
        const char *d = reg_home(fr, v->dest);
        const char *rb = reg_home(fr, v->b);
        if (d && !(rb && strcmp(rb, d) == 0)) {
            char right[64];
            load_temp(fr, v->a, d, out);
            operand_of(fr, v->b, right);
            fprintf(out, "        %s    %s, %s\n", simple_op(v->op), d, right);
            return;
        }
    }
    /* A full-width comparison can read both sides where they already are; the
       answer still has to come out of `al`, which is why it lands in eax when
       the result has no register of its own. */
    if (is_cmp && (t == FE_IR_I32 || t == FE_IR_PTR)) {
        const char *left = reg_home(fr, v->a);
        const char *d = reg_home(fr, v->dest);
        char right[64];
        if (!left) { load_temp(fr, v->a, "eax", out); left = "eax"; }
        operand_of(fr, v->b, right);
        fprintf(out, "        cmp     %s, %s\n", left, right);
        fprintf(out, "        %s   al\n", cmp_set(v->op, v->is_unsigned));
        fprintf(out, "        movzx   %s, al\n", d ? d : "eax");
        if (!d) store_temp(fr, v->dest, "eax", out);
        return;
    }
    load_temp(fr, v->a, "eax", out);
    load_temp(fr, v->b, "ecx", out);
    if (is_cmp) {
        fprintf(out, "        cmp     %s, %s\n", a, c);
        fprintf(out, "        %s   al\n", cmp_set(v->op, v->is_unsigned));
        fprintf(out, "        movzx   eax, al\n");
        store_temp(fr, v->dest, "eax", out);
        return;
    }
    switch (v->op) {
    case FE_IR_ADD: fprintf(out, "        add     %s, %s\n", a, c); break;
    case FE_IR_SUB: fprintf(out, "        sub     %s, %s\n", a, c); break;
    case FE_IR_MUL: fprintf(out, "        imul    %s, %s\n", a, c); break;
    case FE_IR_AND: fprintf(out, "        and     %s, %s\n", a, c); break;
    case FE_IR_OR:  fprintf(out, "        or      %s, %s\n", a, c); break;
    case FE_IR_XOR: fprintf(out, "        xor     %s, %s\n", a, c); break;
    case FE_IR_SHL: fprintf(out, "        shl     %s, cl\n", a); break;
    case FE_IR_SHR:
        fprintf(out, "        %s     %s, cl\n",
                v->is_unsigned ? "shr" : "sar", a);
        break;
    case FE_IR_DIV:
    case FE_IR_MOD:
        /* The divide instructions use edx:eax, so the operands have to be
           widened to 32 bits whatever the declared width is. */
        if (v->is_unsigned) fprintf(out, "        xor     edx, edx\n");
        else fprintf(out, "        cdq\n");
        fprintf(out, "        %s     ecx\n", v->is_unsigned ? "div " : "idiv");
        if (v->op == FE_IR_MOD) fprintf(out, "        mov     eax, edx\n");
        break;
    default: break;
    }
    store_temp(fr, v->dest, "eax", out);
}

static void emit_value(const Frame *fr, const FeIrValue *v, FILE *out)
{
    char addr[128];
    unsigned i;
    switch (v->op) {
    case FE_IR_CONST: {
        const char *d = reg_home(fr, v->dest);
        fprintf(out, "        mov     %s, %ld\n", d ? d : "eax", v->imm);
        if (!d) store_temp(fr, v->dest, "eax", out);
        break;
    }
    case FE_IR_LOAD: {
        const char *d = reg_home(fr, v->dest);
        const char *into = d ? d : "eax";
        load_place_base(fr, &v->place, out);
        place_addr(fr, &v->place, addr);
        if (v->type == FE_IR_I8)
            fprintf(out, "        movzx   %s, byte ptr %s\n", into, addr);
        else if (v->type == FE_IR_I16)
            fprintf(out, "        movzx   %s, word ptr %s\n", into, addr);
        else
            fprintf(out, "        mov     %s, dword ptr %s\n", into, addr);
        if (!d) store_temp(fr, v->dest, "eax", out);
        break;
    }
    case FE_IR_STORE: {
        const char *from = reg_home(fr, v->a);
        load_place_base(fr, &v->place, out);
        place_addr(fr, &v->place, addr);
        /* A full-width value already in a register goes straight out; a narrow
           one needs a byte or word half, which only eax has here. */
        if (from && (v->type == FE_IR_I32 || v->type == FE_IR_PTR)) {
            fprintf(out, "        mov     %s %s, %s\n", word_of(v->type), addr,
                    from);
            break;
        }
        load_temp(fr, v->a, "eax", out);
        fprintf(out, "        mov     %s %s, %s\n", word_of(v->type), addr,
                reg_of(v->type, 0));
        break;
    }
    case FE_IR_ADDR: {
        const char *d = reg_home(fr, v->dest);
        load_place_base(fr, &v->place, out);
        place_addr(fr, &v->place, addr);
        fprintf(out, "        lea     %s, %s\n", d ? d : "eax", addr);
        if (!d) store_temp(fr, v->dest, "eax", out);
        break;
    }
    case FE_IR_CAST:
        load_temp(fr, v->a, "eax", out);
        /* Narrowing is free once everything is kept in a 32-bit slot; widening
           has to say whether the top bits are copies of the sign. */
        if (v->type == FE_IR_I8)
            fprintf(out, "        %s   eax, al\n",
                    v->is_unsigned ? "movzx" : "movsx");
        else if (v->type == FE_IR_I16)
            fprintf(out, "        %s   eax, ax\n",
                    v->is_unsigned ? "movzx" : "movsx");
        store_temp(fr, v->dest, "eax", out);
        break;
    case FE_IR_CALL:
        /* cdecl: arguments pushed right to left, the caller pops them. */
        for (i = v->arg_count; i > 0; --i) {
            load_temp(fr, v->args[i - 1], "eax", out);
            fprintf(out, "        push    eax\n");
        }
        fprintf(out, "        call    %s\n", v->callee);
        if (v->arg_count)
            fprintf(out, "        add     esp, %u\n", v->arg_count * 4U);
        if (v->has_dest) store_temp(fr, v->dest, "eax", out);
        break;
    case FE_IR_COPY: {
        char dst[128];
        char src[128];
        /* Both addresses are worked out in the scratch registers first, and
           only then does the block copy take over esi and edi -- which may be
           holding temporaries, so it hands them back. */
        if (v->place2.base == FE_PLACE_TEMP) {
            load_temp(fr, v->place2.index, "eax", out);
            if (v->place2.offset)
                fprintf(out, "        add     eax, %ld\n", v->place2.offset);
        } else {
            place_addr(fr, &v->place2, src);
            fprintf(out, "        lea     eax, %s\n", src);
        }
        if (v->place.base == FE_PLACE_TEMP) {
            load_temp(fr, v->place.index, "edx", out);
            if (v->place.offset)
                fprintf(out, "        add     edx, %ld\n", v->place.offset);
        } else {
            place_addr(fr, &v->place, dst);
            fprintf(out, "        lea     edx, %s\n", dst);
        }
        fprintf(out, "        push    esi\n");
        fprintf(out, "        push    edi\n");
        fprintf(out, "        mov     esi, eax\n");
        fprintf(out, "        mov     edi, edx\n");
        fprintf(out, "        mov     ecx, %ld\n", v->imm);
        fprintf(out, "        cld\n");
        fprintf(out, "        rep movsb\n");
        fprintf(out, "        pop     edi\n        pop     esi\n");
        break;
    }
    default:
        emit_binary(fr, v, out);
        break;
    }
}

static void emit_func(const FeIrModule *m, const FeIrFunc *f, FILE *out)
{
    Frame fr;
    long *storage;
    const FeIrBlock *b;
    const FeIrValue *v;
    unsigned i;
    long arg = 8;
    if (f->is_extern || !f->first) return;
    /* One offset per local, however many there are. A fixed array here would
       silently stop emitting a function that had too many. */
    storage = (long *)malloc((size_t)(f->local_count ? f->local_count : 1) *
                             sizeof(long));
    if (!storage) return;
    frame_layout(&fr, f, storage);
    allocate_registers(&fr, f);

    fprintf(out, "\npublic %s\n", f->name);
    fprintf(out, "%s proc near\n", f->name);
    fprintf(out, "        push    ebp\n");
    fprintf(out, "        mov     ebp, esp\n");
    if (fr.size) fprintf(out, "        sub     esp, %ld\n", fr.size);
    fprintf(out, "        push    ebx\n        push    esi\n"
                 "        push    edi\n");
    /* Copy the incoming arguments into the frame. */
    for (i = 0; i < f->param_count; ++i) {
        fprintf(out, "        mov     eax, [ebp+%ld]\n", arg);
        fprintf(out, "        mov     %s [ebp%+ld], %s\n",
                word_of(f->locals[i].type), storage[i],
                reg_of(f->locals[i].type, 0));
        arg += 4;
    }

    for (b = f->first; b; b = b->next) {
        fprintf(out, "L%s_%u:\n", f->name, b->id);
        for (v = b->first; v; v = v->next) emit_value(&fr, v, out);
        switch (b->term) {
        case FE_IR_JMP:
            fprintf(out, "        jmp     L%s_%u\n", f->name, b->target);
            break;
        case FE_IR_BR:
            load_temp(&fr, b->cond, "eax", out);
            fprintf(out, "        test    eax, eax\n");
            fprintf(out, "        jnz     L%s_%u\n", f->name, b->target);
            fprintf(out, "        jmp     L%s_%u\n", f->name, b->target_else);
            break;
        case FE_IR_RET:
            if (b->has_ret_value) load_temp(&fr, b->ret_value, "eax", out);
            fprintf(out, "        pop     edi\n        pop     esi\n"
                         "        pop     ebx\n");
            fprintf(out, "        mov     esp, ebp\n        pop     ebp\n");
            fprintf(out, "        ret\n");
            break;
        case FE_IR_TRAP:
            fprintf(out, "        push    %lu\n", b->trap_line);
            fprintf(out, "        push    offset FE_FILE_%u\n",
                    b->trap_file);
            fprintf(out, "        push    %u\n", (unsigned)b->trap);
            fprintf(out, "        call    fe_trap\n");
            fprintf(out, "        add     esp, 12\n");
            break;
        }
    }
    fprintf(out, "%s endp\n", f->name);
    free(storage);
    free(fr.temp_reg);
    (void)m;
}

static void emit_string(const char *s, FILE *out)
{
    int in = 0;
    fputs("        db      ", out);
    for (; s && *s; ++s) {
        unsigned char c = (unsigned char)*s;
        if (c >= 32 && c < 127 && c != '\'' && c != '"') {
            if (!in) { fputc('\'', out); in = 1; }
            fputc(c, out);
        } else {
            if (in) { fputs("',", out); in = 0; }
            fprintf(out, "%u,", c);
        }
    }
    if (in) fputc('\'', out);
    else fputc('0', out);
    if (in) fputs(",0", out);
    fputc('\n', out);
}

void fe_x86_emit(const FeIrModule *m, FILE *out)
{
    const FeIrFunc *f;
    const FeIrGlobal *g;
    int any_trap = 0;
    const FeIrBlock *b;
    unsigned i;

    for (f = m->funcs; f && !any_trap; f = f->next)
        for (b = f->first; b; b = b->next)
            if (b->term == FE_IR_TRAP) { any_trap = 1; break; }

    fputs(".386\n.model flat\n\n", out);
    for (f = m->funcs; f; f = f->next)
        if (f->is_extern || !f->first)
            fprintf(out, "extern %s : near\n", f->name);
    /* Anything called but not defined here lives somewhere else -- the runtime,
       or a library. Lowering emits such calls directly (allocating, writing,
       trapping), so the names are collected from the calls themselves rather
       than from a list that would have to be kept in step. */
    {
        const char *seen[64];
        unsigned count = 0;
        const FeIrValue *v;
        const FeIrFunc *g;
        unsigned i;
        for (f = m->funcs; f; f = f->next)
            for (b = f->first; b; b = b->next)
                for (v = b->first; v; v = v->next) {
                    if (v->op != FE_IR_CALL || !v->callee) continue;
                    for (g = m->funcs; g; g = g->next)
                        if (!strcmp(g->name, v->callee)) break;
                    if (g) continue;
                    for (i = 0; i < count; ++i)
                        if (!strcmp(seen[i], v->callee)) break;
                    if (i < count || count >= 64) continue;
                    seen[count++] = v->callee;
                    fprintf(out, "extern %s : near\n", v->callee);
                }
    }
    if (any_trap) fputs("extern fe_trap : near\n", out);

    fputs("\n_DATA segment dword public 'DATA'\n", out);
    /* One name per file a trap can come from. A build is many units in
       one module, and a trap that names the wrong file is worse than
       one that names none. */
    for (i = 0; i < m->file_count; ++i) {
        fprintf(out, "public FE_FILE_%u\nFE_FILE_%u label byte\n", i, i);
        emit_string(m->files[i], out);
    }
    for (g = m->globals; g; g = g->next) {
        unsigned long i;
        fprintf(out, "public %s\n%s label byte\n", g->name, g->name);
        if (!g->init) {
            fprintf(out, "        db      %lu dup(0)\n", g->size ? g->size : 1UL);
            continue;
        }
        for (i = 0; i < g->size; ) {
            unsigned r;
            unsigned long j;
            for (r = 0; r < g->reloc_count; ++r)
                if (g->relocs[r].at == i) break;
            if (r < g->reloc_count) {
                /* A hole the linker fills with an address. */
                fprintf(out, "        dd      offset %s\n",
                        g->relocs[r].symbol);
                i += 4;
                continue;
            }
            fputs("        db      ", out);
            j = 0;
            while (i < g->size && j < 16) {
                unsigned q;
                for (q = 0; q < g->reloc_count; ++q)
                    if (g->relocs[q].at == i) break;
                if (q < g->reloc_count) break;
                fprintf(out, "%s%u", j ? "," : "", g->init[i]);
                ++i; ++j;
            }
            fputc('\n', out);
        }
        if (!g->size) fputs("        db      0\n", out);
    }
    fputs("_DATA ends\n", out);

    fputs("\n_TEXT segment dword public 'CODE'\n", out);
    for (f = m->funcs; f; f = f->next) emit_func(m, f, out);
    /* The runtime's entry stub calls one fixed name, so point it here. */
    if (m->entry_main)
        fprintf(out, "\npublic fe_main_\nfe_main_ proc near\n"
                     "        jmp     %s\nfe_main_ endp\n", m->entry_main);
    fputs("\n_TEXT ends\n\nend\n", out);
}