summaryrefslogtreecommitdiff
path: root/output/outaout.c
blob: e0963924edb44d5920b8f819843614ac1fd03dc3 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
/* ----------------------------------------------------------------------- *
 *   
 *   Copyright 1996-2009 The NASM Authors - All Rights Reserved
 *   See the file AUTHORS included with the NASM distribution for
 *   the specific copyright holders.
 *
 *   Redistribution and use in source and binary forms, with or without
 *   modification, are permitted provided that the following
 *   conditions are met:
 *
 *   * Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *   * Redistributions in binary form must reproduce the above
 *     copyright notice, this list of conditions and the following
 *     disclaimer in the documentation and/or other materials provided
 *     with the distribution.
 *     
 *     THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
 *     CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
 *     INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 *     MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 *     DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 *     CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 *     SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 *     NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 *     LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 *     HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 *     CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
 *     OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
 *     EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * ----------------------------------------------------------------------- */

/* 
 * outaout.c	output routines for the Netwide Assembler to produce
 *		Linux a.out object files
 */

#include "compiler.h"

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

#include "nasm.h"
#include "nasmlib.h"
#include "saa.h"
#include "raa.h"
#include "stdscan.h"
#include "eval.h"
#include "output/outform.h"
#include "output/outlib.h"

#if defined OF_AOUT || defined OF_AOUTB

#define RELTYPE_ABSOLUTE 0x00
#define RELTYPE_RELATIVE 0x01
#define RELTYPE_GOTPC    0x01   /* no explicit GOTPC in a.out */
#define RELTYPE_GOTOFF   0x10
#define RELTYPE_GOT      0x10   /* distinct from GOTOFF bcos sym not sect */
#define RELTYPE_PLT      0x21
#define RELTYPE_SYMFLAG  0x08

struct Reloc {
    struct Reloc *next;
    int32_t address;               /* relative to _start_ of section */
    int32_t symbol;                /* symbol number or -ve section id */
    int bytes;                  /* 2 or 4 */
    int reltype;                /* see above */
};

struct Symbol {
    int32_t strpos;                /* string table position of name */
    int type;                   /* symbol type - see flags below */
    int32_t value;                 /* address, or COMMON variable size */
    int32_t size;                  /* size for data or function exports */
    int32_t segment;               /* back-reference used by gsym_reloc */
    struct Symbol *next;        /* list of globals in each section */
    struct Symbol *nextfwd;     /* list of unresolved-size symbols */
    char *name;                 /* for unresolved-size symbols */
    int32_t symnum;                /* index into symbol table */
};

/*
 * Section IDs - used in Reloc.symbol when negative, and in
 * Symbol.type when positive.
 */
#define SECT_ABS 2              /* absolute value */
#define SECT_TEXT 4             /* text section */
#define SECT_DATA 6             /* data section */
#define SECT_BSS 8              /* bss section */
#define SECT_MASK 0xE           /* mask out any of the above */

/*
 * More flags used in Symbol.type.
 */
#define SYM_GLOBAL 1            /* it's a global symbol */
#define SYM_DATA 0x100          /* used for shared libs */
#define SYM_FUNCTION 0x200      /* used for shared libs */
#define SYM_WITH_SIZE 0x4000    /* not output; internal only */

/*
 * Bit more explanation of symbol types: SECT_xxx denotes a local
 * symbol. SECT_xxx|SYM_GLOBAL denotes a global symbol, defined in
 * this module. Just SYM_GLOBAL, with zero value, denotes an
 * external symbol referenced in this module. And just SYM_GLOBAL,
 * but with a non-zero value, declares a C `common' variable, of
 * size `value'.
 */

struct Section {
    struct SAA *data;
    uint32_t len, size, nrelocs;
    int32_t index;
    struct Reloc *head, **tail;
    struct Symbol *gsyms, *asym;
};

static struct Section stext, sdata, sbss;

static struct SAA *syms;
static uint32_t nsyms;

static struct RAA *bsym;

static struct SAA *strs;
static uint32_t strslen;

static struct Symbol *fwds;

static int bsd;
static int is_pic;

static void aout_write(void);
static void aout_write_relocs(struct Reloc *);
static void aout_write_syms(void);
static void aout_sect_write(struct Section *, const uint8_t *,
                            uint32_t);
static void aout_pad_sections(void);
static void aout_fixup_relocs(struct Section *);

/*
 * Special section numbers which are used to define special
 * symbols, which can be used with WRT to provide PIC relocation
 * types.
 */
static int32_t aout_gotpc_sect, aout_gotoff_sect;
static int32_t aout_got_sect, aout_plt_sect;
static int32_t aout_sym_sect;

static void aoutg_init(void)
{
    stext.data = saa_init(1L);
    stext.head = NULL;
    stext.tail = &stext.head;
    sdata.data = saa_init(1L);
    sdata.head = NULL;
    sdata.tail = &sdata.head;
    stext.len = stext.size = sdata.len = sdata.size = sbss.len = 0;
    stext.nrelocs = sdata.nrelocs = 0;
    stext.gsyms = sdata.gsyms = sbss.gsyms = NULL;
    stext.index = seg_alloc();
    sdata.index = seg_alloc();
    sbss.index = seg_alloc();
    stext.asym = sdata.asym = sbss.asym = NULL;
    syms = saa_init((int32_t)sizeof(struct Symbol));
    nsyms = 0;
    bsym = raa_init();
    strs = saa_init(1L);
    strslen = 0;
    fwds = NULL;
}

#ifdef OF_AOUT

static void aout_init(void)
{
    bsd = false;
    aoutg_init();

    aout_gotpc_sect = aout_gotoff_sect = aout_got_sect =
        aout_plt_sect = aout_sym_sect = NO_SEG;
}

#endif

#ifdef OF_AOUTB

extern struct ofmt of_aoutb;

static void aoutb_init(void)
{
    bsd = true;
    aoutg_init();

    is_pic = 0x00;              /* may become 0x40 */

    aout_gotpc_sect = seg_alloc();
    define_label("..gotpc", aout_gotpc_sect + 1, 0L, NULL, false, false);
    aout_gotoff_sect = seg_alloc();
    define_label("..gotoff", aout_gotoff_sect + 1, 0L, NULL, false, false);
    aout_got_sect = seg_alloc();
    define_label("..got", aout_got_sect + 1, 0L, NULL, false, false);
    aout_plt_sect = seg_alloc();
    define_label("..plt", aout_plt_sect + 1, 0L, NULL, false, false);
    aout_sym_sect = seg_alloc();
    define_label("..sym", aout_sym_sect + 1, 0L, NULL, false, false);
}

#endif

static void aout_cleanup(int debuginfo)
{
    struct Reloc *r;

    (void)debuginfo;

    aout_pad_sections();
    aout_fixup_relocs(&stext);
    aout_fixup_relocs(&sdata);
    aout_write();
    saa_free(stext.data);
    while (stext.head) {
        r = stext.head;
        stext.head = stext.head->next;
        nasm_free(r);
    }
    saa_free(sdata.data);
    while (sdata.head) {
        r = sdata.head;
        sdata.head = sdata.head->next;
        nasm_free(r);
    }
    saa_free(syms);
    raa_free(bsym);
    saa_free(strs);
}

static int32_t aout_section_names(char *name, int pass, int *bits)
{

    (void)pass;

    /*
     * Default to 32 bits.
     */
    if (!name)
        *bits = 32;

    if (!name)
        return stext.index;

    if (!strcmp(name, ".text"))
        return stext.index;
    else if (!strcmp(name, ".data"))
        return sdata.index;
    else if (!strcmp(name, ".bss"))
        return sbss.index;
    else
        return NO_SEG;
}

static void aout_deflabel(char *name, int32_t segment, int64_t offset,
                          int is_global, char *special)
{
    int pos = strslen + 4;
    struct Symbol *sym;
    int special_used = false;

    if (name[0] == '.' && name[1] == '.' && name[2] != '@') {
        /*
         * This is a NASM special symbol. We never allow it into
         * the a.out symbol table, even if it's a valid one. If it
         * _isn't_ a valid one, we should barf immediately.
         */
        if (strcmp(name, "..gotpc") && strcmp(name, "..gotoff") &&
            strcmp(name, "..got") && strcmp(name, "..plt") &&
            strcmp(name, "..sym"))
            nasm_error(ERR_NONFATAL, "unrecognised special symbol `%s'", name);
        return;
    }

    if (is_global == 3) {
        struct Symbol **s;
        /*
         * Fix up a forward-reference symbol size from the first
         * pass.
         */
        for (s = &fwds; *s; s = &(*s)->nextfwd)
            if (!strcmp((*s)->name, name)) {
                struct tokenval tokval;
                expr *e;
                char *p = special;

                while (*p && !nasm_isspace(*p))
                    p++;
                while (*p && nasm_isspace(*p))
                    p++;
                stdscan_reset();
                stdscan_set(p);
                tokval.t_type = TOKEN_INVALID;
                e = evaluate(stdscan, NULL, &tokval, NULL, 1, nasm_error, NULL);
                if (e) {
                    if (!is_simple(e))
                        nasm_error(ERR_NONFATAL, "cannot use relocatable"
                              " expression as symbol size");
                    else
                        (*s)->size = reloc_value(e);
                }

                /*
                 * Remove it from the list of unresolved sizes.
                 */
                nasm_free((*s)->name);
                *s = (*s)->nextfwd;
                return;
            }
        return;                 /* it wasn't an important one */
    }

    saa_wbytes(strs, name, (int32_t)(1 + strlen(name)));
    strslen += 1 + strlen(name);

    sym = saa_wstruct(syms);

    sym->strpos = pos;
    sym->type = is_global ? SYM_GLOBAL : 0;
    sym->segment = segment;
    if (segment == NO_SEG)
        sym->type |= SECT_ABS;
    else if (segment == stext.index) {
        sym->type |= SECT_TEXT;
        if (is_global) {
            sym->next = stext.gsyms;
            stext.gsyms = sym;
        } else if (!stext.asym)
            stext.asym = sym;
    } else if (segment == sdata.index) {
        sym->type |= SECT_DATA;
        if (is_global) {
            sym->next = sdata.gsyms;
            sdata.gsyms = sym;
        } else if (!sdata.asym)
            sdata.asym = sym;
    } else if (segment == sbss.index) {
        sym->type |= SECT_BSS;
        if (is_global) {
            sym->next = sbss.gsyms;
            sbss.gsyms = sym;
        } else if (!sbss.asym)
            sbss.asym = sym;
    } else
        sym->type = SYM_GLOBAL;
    if (is_global == 2)
        sym->value = offset;
    else
        sym->value = (sym->type == SYM_GLOBAL ? 0 : offset);

    if (is_global && sym->type != SYM_GLOBAL) {
        /*
         * Global symbol exported _from_ this module. We must check
         * the special text for type information.
         */

        if (special) {
            int n = strcspn(special, " ");

            if (!nasm_strnicmp(special, "function", n))
                sym->type |= SYM_FUNCTION;
            else if (!nasm_strnicmp(special, "data", n) ||
                     !nasm_strnicmp(special, "object", n))
                sym->type |= SYM_DATA;
            else
                nasm_error(ERR_NONFATAL, "unrecognised symbol type `%.*s'",
                      n, special);
            if (special[n]) {
                struct tokenval tokval;
                expr *e;
                int fwd = false;
                char *saveme = stdscan_get();

                if (!bsd) {
                    nasm_error(ERR_NONFATAL, "Linux a.out does not support"
                          " symbol size information");
                } else {
                    while (special[n] && nasm_isspace(special[n]))
                        n++;
                    /*
                     * We have a size expression; attempt to
                     * evaluate it.
                     */
                    sym->type |= SYM_WITH_SIZE;
                    stdscan_reset();
                    stdscan_set(special + n);
                    tokval.t_type = TOKEN_INVALID;
                    e = evaluate(stdscan, NULL, &tokval, &fwd, 0, nasm_error,
                                 NULL);
                    if (fwd) {
                        sym->nextfwd = fwds;
                        fwds = sym;
                        sym->name = nasm_strdup(name);
                    } else if (e) {
                        if (!is_simple(e))
                            nasm_error(ERR_NONFATAL, "cannot use relocatable"
                                  " expression as symbol size");
                        else
                            sym->size = reloc_value(e);
                    }
                }
                stdscan_set(saveme);
            }
            special_used = true;
        }
    }

    /*
     * define the references from external-symbol segment numbers
     * to these symbol records.
     */
    if (segment != NO_SEG && segment != stext.index &&
        segment != sdata.index && segment != sbss.index)
        bsym = raa_write(bsym, segment, nsyms);
    sym->symnum = nsyms;

    nsyms++;
    if (sym->type & SYM_WITH_SIZE)
        nsyms++;                /* and another for the size */

    if (special && !special_used)
        nasm_error(ERR_NONFATAL, "no special symbol features supported here");
}

static void aout_add_reloc(struct Section *sect, int32_t segment,
                           int reltype, int bytes)
{
    struct Reloc *r;

    r = *sect->tail = nasm_malloc(sizeof(struct Reloc));
    sect->tail = &r->next;
    r->next = NULL;

    r->address = sect->len;
    r->symbol = (segment == NO_SEG ? -SECT_ABS :
                 segment == stext.index ? -SECT_TEXT :
                 segment == sdata.index ? -SECT_DATA :
                 segment == sbss.index ? -SECT_BSS :
                 raa_read(bsym, segment));
    r->reltype = reltype;
    if (r->symbol >= 0)
        r->reltype |= RELTYPE_SYMFLAG;
    r->bytes = bytes;

    sect->nrelocs++;
}

/*
 * This routine deals with ..got and ..sym relocations: the more
 * complicated kinds. In shared-library writing, some relocations
 * with respect to global symbols must refer to the precise symbol
 * rather than referring to an offset from the base of the section
 * _containing_ the symbol. Such relocations call to this routine,
 * which searches the symbol list for the symbol in question.
 *
 * RELTYPE_GOT references require the _exact_ symbol address to be
 * used; RELTYPE_ABSOLUTE references can be at an offset from the
 * symbol. The boolean argument `exact' tells us this.
 *
 * Return value is the adjusted value of `addr', having become an
 * offset from the symbol rather than the section. Should always be
 * zero when returning from an exact call.
 *
 * Limitation: if you define two symbols at the same place,
 * confusion will occur.
 *
 * Inefficiency: we search, currently, using a linked list which
 * isn't even necessarily sorted.
 */
static int32_t aout_add_gsym_reloc(struct Section *sect,
                                int32_t segment, int32_t offset,
                                int type, int bytes, int exact)
{
    struct Symbol *sym, *sm, *shead;
    struct Reloc *r;

    /*
     * First look up the segment to find whether it's text, data,
     * bss or an external symbol.
     */
    shead = NULL;
    if (segment == stext.index)
        shead = stext.gsyms;
    else if (segment == sdata.index)
        shead = sdata.gsyms;
    else if (segment == sbss.index)
        shead = sbss.gsyms;
    if (!shead) {
        if (exact && offset != 0)
            nasm_error(ERR_NONFATAL, "unable to find a suitable global symbol"
                  " for this reference");
        else
            aout_add_reloc(sect, segment, type, bytes);
        return offset;
    }

    if (exact) {
        /*
         * Find a symbol pointing _exactly_ at this one.
         */
        list_for_each(sym, shead)
            if (sym->value == offset)
                break;
    } else {
        /*
         * Find the nearest symbol below this one.
         */
        sym = NULL;
        list_for_each(sm, shead)
            if (sm->value <= offset && (!sym || sm->value > sym->value))
                sym = sm;
    }
    if (!sym && exact) {
        nasm_error(ERR_NONFATAL, "unable to find a suitable global symbol"
              " for this reference");
        return 0;
    }

    r = *sect->tail = nasm_malloc(sizeof(struct Reloc));
    sect->tail = &r->next;
    r->next = NULL;

    r->address = sect->len;
    r->symbol = sym->symnum;
    r->reltype = type | RELTYPE_SYMFLAG;
    r->bytes = bytes;

    sect->nrelocs++;

    return offset - sym->value;
}

/*
 * This routine deals with ..gotoff relocations. These _must_ refer
 * to a symbol, due to a perversity of *BSD's PIC implementation,
 * and it must be a non-global one as well; so we store `asym', the
 * first nonglobal symbol defined in each section, and always work
 * from that. Relocation type is always RELTYPE_GOTOFF.
 *
 * Return value is the adjusted value of `addr', having become an
 * offset from the `asym' symbol rather than the section.
 */
static int32_t aout_add_gotoff_reloc(struct Section *sect, int32_t segment,
                                  int32_t offset, int bytes)
{
    struct Reloc *r;
    struct Symbol *asym;

    /*
     * First look up the segment to find whether it's text, data,
     * bss or an external symbol.
     */
    asym = NULL;
    if (segment == stext.index)
        asym = stext.asym;
    else if (segment == sdata.index)
        asym = sdata.asym;
    else if (segment == sbss.index)
        asym = sbss.asym;
    if (!asym)
        nasm_error(ERR_NONFATAL, "`..gotoff' relocations require a non-global"
              " symbol in the section");

    r = *sect->tail = nasm_malloc(sizeof(struct Reloc));
    sect->tail = &r->next;
    r->next = NULL;

    r->address = sect->len;
    r->symbol = asym->symnum;
    r->reltype = RELTYPE_GOTOFF;
    r->bytes = bytes;

    sect->nrelocs++;

    return offset - asym->value;
}

static void aout_out(int32_t segto, const void *data,
		     enum out_type type, uint64_t size,
                     int32_t segment, int32_t wrt)
{
    struct Section *s;
    int32_t addr;
    uint8_t mydata[4], *p;

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

    if (segto == stext.index)
        s = &stext;
    else if (segto == sdata.index)
        s = &sdata;
    else if (segto == sbss.index)
        s = NULL;
    else {
        nasm_error(ERR_WARNING, "attempt to assemble code in"
              " segment %d: defaulting to `.text'", segto);
        s = &stext;
    }

    if (!s && type != OUT_RESERVE) {
        nasm_error(ERR_WARNING, "attempt to initialize memory in the"
              " BSS section: ignored");
        sbss.len += realsize(type, size);
        return;
    }

    if (type == OUT_RESERVE) {
        if (s) {
            nasm_error(ERR_WARNING, "uninitialized space declared in"
                  " %s section: zeroing",
                  (segto == stext.index ? "code" : "data"));
            aout_sect_write(s, NULL, size);
        } else
            sbss.len += size;
    } else if (type == OUT_RAWDATA) {
        if (segment != NO_SEG)
            nasm_error(ERR_PANIC, "OUT_RAWDATA with other than NO_SEG");
        aout_sect_write(s, data, size);
    } else if (type == OUT_ADDRESS) {
        addr = *(int64_t *)data;
        if (segment != NO_SEG) {
            if (segment % 2) {
                nasm_error(ERR_NONFATAL, "a.out format does not support"
                      " segment base references");
            } else {
                if (wrt == NO_SEG) {
                    aout_add_reloc(s, segment, RELTYPE_ABSOLUTE,
                                   size);
                } else if (!bsd) {
                    nasm_error(ERR_NONFATAL,
                          "Linux a.out format does not support"
                          " any use of WRT");
                    wrt = NO_SEG;       /* we can at least _try_ to continue */
                } else if (wrt == aout_gotpc_sect + 1) {
                    is_pic = 0x40;
                    aout_add_reloc(s, segment, RELTYPE_GOTPC, size);
                } else if (wrt == aout_gotoff_sect + 1) {
                    is_pic = 0x40;
                    addr = aout_add_gotoff_reloc(s, segment,
                                                 addr, size);
                } else if (wrt == aout_got_sect + 1) {
                    is_pic = 0x40;
                    addr =
                        aout_add_gsym_reloc(s, segment, addr, RELTYPE_GOT,
                                            size, true);
                } else if (wrt == aout_sym_sect + 1) {
                    addr = aout_add_gsym_reloc(s, segment, addr,
                                               RELTYPE_ABSOLUTE, size,
                                               false);
                } else if (wrt == aout_plt_sect + 1) {
                    is_pic = 0x40;
                    nasm_error(ERR_NONFATAL,
                          "a.out format cannot produce non-PC-"
                          "relative PLT references");
                } else {
                    nasm_error(ERR_NONFATAL,
                          "a.out format does not support this"
                          " use of WRT");
                    wrt = NO_SEG;       /* we can at least _try_ to continue */
                }
            }
        }
        p = mydata;
        if (size == 2)
            WRITESHORT(p, addr);
        else
            WRITELONG(p, addr);
        aout_sect_write(s, mydata, size);
    } else if (type == OUT_REL2ADR) {
        if (segment == segto)
            nasm_error(ERR_PANIC, "intra-segment OUT_REL2ADR");
        if (segment != NO_SEG && segment % 2) {
            nasm_error(ERR_NONFATAL, "a.out format does not support"
                  " segment base references");
        } else {
            if (wrt == NO_SEG) {
                aout_add_reloc(s, segment, RELTYPE_RELATIVE, 2);
            } else if (!bsd) {
                nasm_error(ERR_NONFATAL, "Linux a.out format does not support"
                      " any use of WRT");
                wrt = NO_SEG;   /* we can at least _try_ to continue */
            } else if (wrt == aout_plt_sect + 1) {
                is_pic = 0x40;
                aout_add_reloc(s, segment, RELTYPE_PLT, 2);
            } else if (wrt == aout_gotpc_sect + 1 ||
                       wrt == aout_gotoff_sect + 1 ||
                       wrt == aout_got_sect + 1) {
                nasm_error(ERR_NONFATAL, "a.out format cannot produce PC-"
                      "relative GOT references");
            } else {
                nasm_error(ERR_NONFATAL, "a.out format does not support this"
                      " use of WRT");
                wrt = NO_SEG;   /* we can at least _try_ to continue */
            }
        }
        p = mydata;
        WRITESHORT(p, *(int64_t *)data - (size + s->len));
        aout_sect_write(s, mydata, 2L);
    } else if (type == OUT_REL4ADR) {
        if (segment == segto)
            nasm_error(ERR_PANIC, "intra-segment OUT_REL4ADR");
        if (segment != NO_SEG && segment % 2) {
            nasm_error(ERR_NONFATAL, "a.out format does not support"
                  " segment base references");
        } else {
            if (wrt == NO_SEG) {
                aout_add_reloc(s, segment, RELTYPE_RELATIVE, 4);
            } else if (!bsd) {
                nasm_error(ERR_NONFATAL, "Linux a.out format does not support"
                      " any use of WRT");
                wrt = NO_SEG;   /* we can at least _try_ to continue */
            } else if (wrt == aout_plt_sect + 1) {
                is_pic = 0x40;
                aout_add_reloc(s, segment, RELTYPE_PLT, 4);
            } else if (wrt == aout_gotpc_sect + 1 ||
                       wrt == aout_gotoff_sect + 1 ||
                       wrt == aout_got_sect + 1) {
                nasm_error(ERR_NONFATAL, "a.out format cannot produce PC-"
                      "relative GOT references");
            } else {
                nasm_error(ERR_NONFATAL, "a.out format does not support this"
                      " use of WRT");
                wrt = NO_SEG;   /* we can at least _try_ to continue */
            }
        }
        p = mydata;
        WRITELONG(p, *(int64_t *)data - (size + s->len));
        aout_sect_write(s, mydata, 4L);
    }
}

static void aout_pad_sections(void)
{
    static uint8_t pad[] = { 0x90, 0x90, 0x90, 0x90 };
    /*
     * Pad each of the text and data sections with NOPs until their
     * length is a multiple of four. (NOP == 0x90.) Also increase
     * the length of the BSS section similarly.
     */
    aout_sect_write(&stext, pad, (-(int32_t)stext.len) & 3);
    aout_sect_write(&sdata, pad, (-(int32_t)sdata.len) & 3);
    sbss.len = ALIGN(sbss.len, 4);
}

/*
 * a.out files have the curious property that all references to
 * things in the data or bss sections are done by addresses which
 * are actually relative to the start of the _text_ section, in the
 * _file_. (No relation to what happens after linking. No idea why
 * this should be so. It's very strange.) So we have to go through
 * the relocation table, _after_ the final size of each section is
 * known, and fix up the relocations pointed to.
 */
static void aout_fixup_relocs(struct Section *sect)
{
    struct Reloc *r;

    saa_rewind(sect->data);
    list_for_each(r, sect->head) {
        uint8_t *p, *q, blk[4];
        int32_t l;

        saa_fread(sect->data, r->address, blk, (int32_t)r->bytes);
        p = q = blk;
        l = *p++;
        if (r->bytes > 1) {
            l += ((int32_t)*p++) << 8;
            if (r->bytes == 4) {
                l += ((int32_t)*p++) << 16;
                l += ((int32_t)*p++) << 24;
            }
        }
        if (r->symbol == -SECT_DATA)
            l += stext.len;
        else if (r->symbol == -SECT_BSS)
            l += stext.len + sdata.len;
        if (r->bytes == 4)
            WRITELONG(q, l);
        else if (r->bytes == 2)
            WRITESHORT(q, l);
        else
            *q++ = l & 0xFF;
        saa_fwrite(sect->data, r->address, blk, (int32_t)r->bytes);
    }
}

static void aout_write(void)
{
    /*
     * Emit the a.out header.
     */
    /* OMAGIC, M_386 or MID_I386, no flags */
    fwriteint32_t(bsd ? 0x07018600 | is_pic : 0x640107L, ofile);
    fwriteint32_t(stext.len, ofile);
    fwriteint32_t(sdata.len, ofile);
    fwriteint32_t(sbss.len, ofile);
    fwriteint32_t(nsyms * 12, ofile);     /* length of symbol table */
    fwriteint32_t(0L, ofile);     /* object files have no entry point */
    fwriteint32_t(stext.nrelocs * 8, ofile);      /* size of text relocs */
    fwriteint32_t(sdata.nrelocs * 8, ofile);      /* size of data relocs */

    /*
     * Write out the code section and the data section.
     */
    saa_fpwrite(stext.data, ofile);
    saa_fpwrite(sdata.data, ofile);

    /*
     * Write out the relocations.
     */
    aout_write_relocs(stext.head);
    aout_write_relocs(sdata.head);

    /*
     * Write the symbol table.
     */
    aout_write_syms();

    /*
     * And the string table.
     */
    fwriteint32_t(strslen + 4, ofile);    /* length includes length count */
    saa_fpwrite(strs, ofile);
}

static void aout_write_relocs(struct Reloc *r)
{
    list_for_each(r, r) {
        uint32_t word2;

        fwriteint32_t(r->address, ofile);

        if (r->symbol >= 0)
            word2 = r->symbol;
        else
            word2 = -r->symbol;
        word2 |= r->reltype << 24;
        word2 |= (r->bytes == 1 ? 0 :
                  r->bytes == 2 ? 0x2000000L : 0x4000000L);
        fwriteint32_t(word2, ofile);
    }
}

static void aout_write_syms(void)
{
    uint32_t i;

    saa_rewind(syms);
    for (i = 0; i < nsyms; i++) {
        struct Symbol *sym = saa_rstruct(syms);
        fwriteint32_t(sym->strpos, ofile);
        fwriteint32_t((int32_t)sym->type & ~SYM_WITH_SIZE, ofile);
        /*
         * Fix up the symbol value now we know the final section
         * sizes.
         */
        if ((sym->type & SECT_MASK) == SECT_DATA)
            sym->value += stext.len;
        if ((sym->type & SECT_MASK) == SECT_BSS)
            sym->value += stext.len + sdata.len;
        fwriteint32_t(sym->value, ofile);
        /*
         * Output a size record if necessary.
         */
        if (sym->type & SYM_WITH_SIZE) {
            fwriteint32_t(sym->strpos, ofile);
            fwriteint32_t(0x0DL, ofile);  /* special value: means size */
            fwriteint32_t(sym->size, ofile);
            i++;                /* use up another of `nsyms' */
        }
    }
}

static void aout_sect_write(struct Section *sect,
                            const uint8_t *data, uint32_t len)
{
    saa_wbytes(sect->data, data, len);
    sect->len += len;
}

static int32_t aout_segbase(int32_t segment)
{
    return segment;
}

static void aout_filename(char *inname, char *outname)
{
    standard_extension(inname, outname, ".o");
}

extern macros_t aout_stdmac[];

#endif                          /* OF_AOUT || OF_AOUTB */

#ifdef OF_AOUT

struct ofmt of_aout = {
    "Linux a.out object files",
    "aout",
    0,
    null_debug_arr,
    &null_debug_form,
    aout_stdmac,
    aout_init,
    null_setinfo,
    aout_out,
    aout_deflabel,
    aout_section_names,
    null_sectalign,
    aout_segbase,
    null_directive,
    aout_filename,
    aout_cleanup
};

#endif

#ifdef OF_AOUTB

struct ofmt of_aoutb = {
    "NetBSD/FreeBSD a.out object files",
    "aoutb",
    0,
    null_debug_arr,
    &null_debug_form,
    aout_stdmac,
    aoutb_init,
    null_setinfo,
    aout_out,
    aout_deflabel,
    aout_section_names,
    null_sectalign,
    aout_segbase,
    null_directive,
    aout_filename,
    aout_cleanup
};

#endif