outaout.c

   1 /* outaout.c    output routines for the Netwide Assembler to produce
   2  *              Linux a.out object files
   3  *
   4  * The Netwide Assembler is copyright (C) 1996 Simon Tatham and
   5  * Julian Hall. All rights reserved. The software is
   6  * redistributable under the licence given in the file "Licence"
   7  * distributed in the NASM archive.
   8  */
   9
  10 #include <stdio.h>
  11 #include <stdlib.h>
  12 #include <string.h>
  13 #include <ctype.h>
  14
  15 #include "nasm.h"
  16 #include "nasmlib.h"
  17 #include "outform.h"
  18
  19 #ifdef OF_AOUT
  20
  21 struct Reloc {
  22     struct Reloc *next;
  23     long address;                      /* relative to _start_ of section */
  24     long symbol;                       /* symbol number or -ve section id */
  25     int bytes;                         /* 2 or 4 */
  26     int relative;                      /* TRUE or FALSE */
  27 };
  28
  29 struct Symbol {
  30     long strpos;                       /* string table position of name */
  31     int type;                          /* symbol type - see flags below */
  32     long value;                        /* address, or COMMON variable size */
  33 };
  34
  35 /*
  36  * Section IDs - used in Reloc.symbol when negative, and in
  37  * Symbol.type when positive.
  38  */
  39 #define SECT_ABS 2                     /* absolute value */
  40 #define SECT_TEXT 4                    /* text section */
  41 #define SECT_DATA 6                    /* data section */
  42 #define SECT_BSS 8                     /* bss section */
  43 #define SECT_MASK 0xE                  /* mask out any of the above */
  44
  45 /*
  46  * Another flag used in Symbol.type.
  47  */
  48 #define SYM_GLOBAL 1                   /* it's a global symbol */
  49
  50 /*
  51  * Bit more explanation of symbol types: SECT_xxx denotes a local
  52  * symbol. SECT_xxx|SYM_GLOBAL denotes a global symbol, defined in
  53  * this module. Just SYM_GLOBAL, with zero value, denotes an
  54  * external symbol referenced in this module. And just SYM_GLOBAL,
  55  * but with a non-zero value, declares a C `common' variable, of
  56  * size `value'.
  57  */
  58
  59 struct Section {
  60     struct SAA *data;
  61     unsigned long len, size, nrelocs;
  62     long index;
  63     struct Reloc *head, **tail;
  64 };
  65
  66 static struct Section stext, sdata;
  67 static unsigned long bsslen;
  68 static long bssindex;
  69
  70 static struct SAA *syms;
  71 static unsigned long nsyms;
  72
  73 static struct RAA *bsym;
  74
  75 static struct SAA *strs;
  76 static unsigned long strslen;
  77
  78 static FILE *aoutfp;
  79 static efunc error;
  80
  81 static void aout_write(void);
  82 static void aout_write_relocs(struct Reloc *);
  83 static void aout_write_syms(void);
  84 static void aout_sect_write(struct Section *, unsigned char *, unsigned long);
  85 static void aout_pad_sections(void);
  86 static void aout_fixup_relocs(struct Section *);
  87
  88 static void aout_init(FILE *fp, efunc errfunc, ldfunc ldef) {
  89     aoutfp = fp;
  90     error = errfunc;
  91     (void) ldef;                       /* placate optimisers */
  92     stext.data = saa_init(1L); stext.head = NULL; stext.tail = &stext.head;
  93     sdata.data = saa_init(1L); sdata.head = NULL; sdata.tail = &sdata.head;
  94     stext.len = stext.size = sdata.len = sdata.size = bsslen = 0;
  95     stext.nrelocs = sdata.nrelocs = 0;
  96     stext.index = seg_alloc();
  97     sdata.index = seg_alloc();
  98     bssindex = seg_alloc();
  99     syms = saa_init((long)sizeof(struct Symbol));
 100     nsyms = 0;
 101     bsym = raa_init();
 102     strs = saa_init(1L);
 103     strslen = 0;
 104 }
 105
 106 static void aout_cleanup(void) {
 107     struct Reloc *r;
 108
 109     aout_pad_sections();
 110     aout_fixup_relocs(&stext);
 111     aout_fixup_relocs(&sdata);
 112     aout_write();
 113     fclose (aoutfp);
 114     saa_free (stext.data);
 115     while (stext.head) {
 116         r = stext.head;
 117         stext.head = stext.head->next;
 118         nasm_free (r);
 119     }
 120     saa_free (sdata.data);
 121     while (sdata.head) {
 122         r = sdata.head;
 123         sdata.head = sdata.head->next;
 124         nasm_free (r);
 125     }
 126     saa_free (syms);
 127     raa_free (bsym);
 128     saa_free (strs);
 129 }
 130
 131 static long aout_section_names (char *name, int pass, int *bits) {
 132     /*
 133      * Default to 32 bits.
 134      */
 135     if (!name)
 136         *bits = 32;
 137
 138     if (!name)
 139         return stext.index;
 140
 141     if (!strcmp(name, ".text"))
 142         return stext.index;
 143     else if (!strcmp(name, ".data"))
 144         return sdata.index;
 145     else if (!strcmp(name, ".bss"))
 146         return bssindex;
 147     else
 148         return NO_SEG;
 149 }
 150
 151 static void aout_deflabel (char *name, long segment, long offset,
 152                            int is_global) {
 153     int pos = strslen+4;
 154     struct Symbol *sym;
 155
 156     if (name[0] == '.' && name[1] == '.') {
 157         return;
 158     }
 159
 160     saa_wbytes (strs, name, (long)(1+strlen(name)));
 161     strslen += 1+strlen(name);
 162
 163     sym = saa_wstruct (syms);
 164
 165     sym->strpos = pos;
 166     sym->type = is_global ? SYM_GLOBAL : 0;
 167     if (segment == NO_SEG)
 168         sym->type |= SECT_ABS;
 169     else if (segment == stext.index)
 170         sym->type |= SECT_TEXT;
 171     else if (segment == sdata.index)
 172         sym->type |= SECT_DATA;
 173     else if (segment == bssindex)
 174         sym->type |= SECT_BSS;
 175     else
 176         sym->type = SYM_GLOBAL;
 177     if (is_global == 2)
 178         sym->value = offset;
 179     else
 180         sym->value = (sym->type == SYM_GLOBAL ? 0 : offset);
 181
 182     /*
 183      * define the references from external-symbol segment numbers
 184      * to these symbol records.
 185      */
 186     if (segment != NO_SEG && segment != stext.index &&
 187         segment != sdata.index && segment != bssindex)
 188         bsym = raa_write (bsym, segment, nsyms);
 189
 190     nsyms++;
 191 }
 192
 193 static void aout_add_reloc (struct Section *sect, long segment,
 194                             int relative, int bytes) {
 195     struct Reloc *r;
 196
 197     r = *sect->tail = nasm_malloc(sizeof(struct Reloc));
 198     sect->tail = &r->next;
 199     r->next = NULL;
 200
 201     r->address = sect->len;
 202     r->symbol = (segment == NO_SEG ? -SECT_ABS :
 203                  segment == stext.index ? -SECT_TEXT :
 204                  segment == sdata.index ? -SECT_DATA :
 205                  segment == bssindex ? -SECT_BSS :
 206                  raa_read(bsym, segment));
 207     r->relative = relative;
 208     r->bytes = bytes;
 209
 210     sect->nrelocs++;
 211 }
 212
 213 static void aout_out (long segto, void *data, unsigned long type,
 214                       long segment, long wrt) {
 215     struct Section *s;
 216     long realbytes = type & OUT_SIZMASK;
 217     unsigned char mydata[4], *p;
 218
 219     if (wrt != NO_SEG) {
 220         wrt = NO_SEG;                  /* continue to do _something_ */
 221         error (ERR_NONFATAL, "WRT not supported by a.out output format");
 222     }
 223
 224     type &= OUT_TYPMASK;
 225
 226     /*
 227      * handle absolute-assembly (structure definitions)
 228      */
 229     if (segto == NO_SEG) {
 230         if (type != OUT_RESERVE)
 231             error (ERR_NONFATAL, "attempt to assemble code in [ABSOLUTE]"
 232                    " space");
 233         return;
 234     }
 235
 236     if (segto == stext.index)
 237         s = &stext;
 238     else if (segto == sdata.index)
 239         s = &sdata;
 240     else if (segto == bssindex)
 241         s = NULL;
 242     else {
 243         error(ERR_WARNING, "attempt to assemble code in"
 244               " segment %d: defaulting to `.text'", segto);
 245         s = &stext;
 246     }
 247
 248     if (!s && type != OUT_RESERVE) {
 249         error(ERR_WARNING, "attempt to initialise memory in the"
 250               " BSS section: ignored");
 251         if (type == OUT_REL2ADR)
 252             realbytes = 2;
 253         else if (type == OUT_REL4ADR)
 254             realbytes = 4;
 255         bsslen += realbytes;
 256         return;
 257     }
 258
 259     if (type == OUT_RESERVE) {
 260         if (s) {
 261             error(ERR_WARNING, "uninitialised space declared in"
 262                   " %s section: zeroing",
 263                   (segto == stext.index ? "code" : "data"));
 264             aout_sect_write (s, NULL, realbytes);
 265         } else
 266             bsslen += realbytes;
 267     } else if (type == OUT_RAWDATA) {
 268         if (segment != NO_SEG)
 269             error(ERR_PANIC, "OUT_RAWDATA with other than NO_SEG");
 270         aout_sect_write (s, data, realbytes);
 271     } else if (type == OUT_ADDRESS) {
 272         if (segment != NO_SEG) {
 273             if (segment % 2) {
 274                 error(ERR_NONFATAL, "a.out format does not support"
 275                       " segment base references");
 276             } else
 277                 aout_add_reloc (s, segment, FALSE, realbytes);
 278         }
 279         p = mydata;
 280         if (realbytes == 2)
 281             WRITESHORT (p, *(long *)data);
 282         else
 283             WRITELONG (p, *(long *)data);
 284         aout_sect_write (s, mydata, realbytes);
 285     } else if (type == OUT_REL2ADR) {
 286         if (segment == segto)
 287             error(ERR_PANIC, "intra-segment OUT_REL2ADR");
 288         if (segment != NO_SEG && segment % 2) {
 289             error(ERR_NONFATAL, "a.out format does not support"
 290                   " segment base references");
 291         } else
 292             aout_add_reloc (s, segment, TRUE, 2);
 293         p = mydata;
 294         WRITESHORT (p, *(long*)data-(realbytes + s->len));
 295         aout_sect_write (s, mydata, 2L);
 296     } else if (type == OUT_REL4ADR) {
 297         if (segment == segto)
 298             error(ERR_PANIC, "intra-segment OUT_REL4ADR");
 299         if (segment != NO_SEG && segment % 2) {
 300             error(ERR_NONFATAL, "a.out format does not support"
 301                   " segment base references");
 302         } else
 303             aout_add_reloc (s, segment, TRUE, 4);
 304         p = mydata;
 305         WRITELONG (p, *(long*)data-(realbytes + s->len));
 306         aout_sect_write (s, mydata, 4L);
 307     }
 308 }
 309
 310 static void aout_pad_sections(void) {
 311     static unsigned char pad[] = { 0x90, 0x90, 0x90, 0x90 };
 312     /*
 313      * Pad each of the text and data sections with NOPs until their
 314      * length is a multiple of four. (NOP == 0x90.) Also increase
 315      * the length of the BSS section similarly.
 316      */
 317     aout_sect_write (&stext, pad, (-stext.len) & 3);
 318     aout_sect_write (&sdata, pad, (-sdata.len) & 3);
 319     bsslen = (bsslen + 3) & ~3;
 320 }
 321
 322 /*
 323  * a.out files have the curious property that all references to
 324  * things in the data or bss sections are done by addresses which
 325  * are actually relative to the start of the _text_ section, in the
 326  * _file_. (No relation to what happens after linking. No idea why
 327  * this should be so. It's very strange.) So we have to go through
 328  * the relocation table, _after_ the final size of each section is
 329  * known, and fix up the relocations pointed to.
 330  */
 331 static void aout_fixup_relocs(struct Section *sect) {
 332     struct Reloc *r;
 333
 334     saa_rewind (sect->data);
 335     for (r = sect->head; r; r = r->next) {
 336         unsigned char *p, *q, blk[4];
 337         long l;
 338
 339         saa_fread (sect->data, r->address, blk, (long)r->bytes);
 340         p = q = blk;
 341         l = *p++;
 342         l += ((long)*p++) << 8;
 343         if (r->bytes == 4) {
 344             l += ((long)*p++) << 16;
 345             l += ((long)*p++) << 24;
 346         }
 347         if (r->symbol == -SECT_DATA)
 348             l += stext.len;
 349         else if (r->symbol == -SECT_BSS)
 350             l += stext.len + sdata.len;
 351         if (r->bytes == 4)
 352             WRITELONG(q, l);
 353         else
 354             WRITESHORT(q, l);
 355         saa_fwrite (sect->data, r->address, blk, (long)r->bytes);
 356     }
 357 }
 358
 359 static void aout_write(void) {
 360     /*
 361      * Emit the a.out header.
 362      */
 363     fwritelong (0x640107, aoutfp);     /* OMAGIC, M_386, no flags */
 364     fwritelong (stext.len, aoutfp);
 365     fwritelong (sdata.len, aoutfp);
 366     fwritelong (bsslen, aoutfp);
 367     fwritelong (nsyms * 12, aoutfp);   /* length of symbol table */
 368     fwritelong (0L, aoutfp);           /* object files have no entry point */
 369     fwritelong (stext.nrelocs * 8, aoutfp);   /* size of text relocs */
 370     fwritelong (sdata.nrelocs * 8, aoutfp);   /* size of data relocs */
 371
 372     /*
 373      * Write out the code section and the data section.
 374      */
 375     saa_fpwrite (stext.data, aoutfp);
 376     saa_fpwrite (sdata.data, aoutfp);
 377
 378     /*
 379      * Write out the relocations.
 380      */
 381     aout_write_relocs (stext.head);
 382     aout_write_relocs (sdata.head);
 383
 384     /*
 385      * Write the symbol table.
 386      */
 387     aout_write_syms ();
 388
 389     /*
 390      * And the string table.
 391      */
 392     fwritelong (strslen+4, aoutfp);    /* length includes length count */
 393     saa_fpwrite (strs, aoutfp);
 394 }
 395
 396 static void aout_write_relocs (struct Reloc *r) {
 397     while (r) {
 398         unsigned long word2;
 399
 400         fwritelong (r->address, aoutfp);
 401
 402         if (r->symbol >= 0)
 403             word2 = r->symbol | 0x8000000;
 404         else
 405             word2 = -r->symbol;
 406         if (r->relative)
 407             word2 |= 0x1000000;
 408         word2 |= (r->bytes == 2 ? 0x2000000 : 0x4000000);
 409         fwritelong (word2, aoutfp);
 410
 411         r = r->next;
 412     }
 413 }
 414
 415 static void aout_write_syms (void) {
 416     int i;
 417
 418     saa_rewind (syms);
 419     for (i=0; i<nsyms; i++) {
 420         struct Symbol *sym = saa_rstruct(syms);
 421         fwritelong (sym->strpos, aoutfp);
 422         fwritelong ((long)sym->type, aoutfp);
 423         /*
 424          * Fix up the symbol value now we know the final section
 425          * sizes.
 426          */
 427         if ((sym->type & SECT_MASK) == SECT_DATA)
 428             sym->value += stext.len;
 429         if ((sym->type & SECT_MASK) == SECT_BSS)
 430             sym->value += stext.len + sdata.len;
 431         fwritelong (sym->value, aoutfp);
 432     }
 433 }
 434
 435 static void aout_sect_write (struct Section *sect,
 436                              unsigned char *data, unsigned long len) {
 437     saa_wbytes (sect->data, data, len);
 438     sect->len += len;
 439 }
 440
 441 static long aout_segbase (long segment) {
 442     return segment;
 443 }
 444
 445 static int aout_directive (char *directive, char *value, int pass) {
 446     return 0;
 447 }
 448
 449 static void aout_filename (char *inname, char *outname, efunc error) {
 450     standard_extension (inname, outname, ".o", error);
 451 }
 452
 453 struct ofmt of_aout = {
 454     "GNU a.out (i386) object files (e.g. Linux)",
 455     "aout",
 456     aout_init,
 457     aout_out,
 458     aout_deflabel,
 459     aout_section_names,
 460     aout_segbase,
 461     aout_directive,
 462     aout_filename,
 463     aout_cleanup
 464 };
 465
 466 #endif /* OF_AOUT */