libiberty/simple-object-coff.c

   1 /* simple-object-coff.c -- routines to manipulate COFF object files.
   2    Copyright (C) 2010-2017 Free Software Foundation, Inc.
   3    Written by Ian Lance Taylor, Google.
   4
   5 This program is free software; you can redistribute it and/or modify it
   6 under the terms of the GNU General Public License as published by the
   7 Free Software Foundation; either version 2, or (at your option) any
   8 later version.
   9
  10 This program is distributed in the hope that it will be useful,
  11 but WITHOUT ANY WARRANTY; without even the implied warranty of
  12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13 GNU General Public License for more details.
  14
  15 You should have received a copy of the GNU General Public License
  16 along with this program; if not, write to the Free Software
  17 Foundation, 51 Franklin Street - Fifth Floor,
  18 Boston, MA 02110-1301, USA.  */
  19
  20 #include "config.h"
  21 #include "libiberty.h"
  22 #include "simple-object.h"
  23
  24 #include <errno.h>
  25 #include <stddef.h>
  26
  27 #ifdef HAVE_STDLIB_H
  28 #include <stdlib.h>
  29 #endif
  30
  31 #ifdef HAVE_STDINT_H
  32 #include <stdint.h>
  33 #endif
  34
  35 #ifdef HAVE_STRING_H
  36 #include <string.h>
  37 #endif
  38
  39 #ifdef HAVE_INTTYPES_H
  40 #include <inttypes.h>
  41 #endif
  42
  43 #include "simple-object-common.h"
  44
  45 /* COFF structures and constants.  */
  46
  47 /* COFF file header.  */
  48
  49 struct external_filehdr
  50 {
  51   unsigned char f_magic[2];     /* magic number                 */
  52   unsigned char f_nscns[2];     /* number of sections           */
  53   unsigned char f_timdat[4];    /* time & date stamp            */
  54   unsigned char f_symptr[4];    /* file pointer to symtab       */
  55   unsigned char f_nsyms[4];     /* number of symtab entries     */
  56   unsigned char f_opthdr[2];    /* sizeof(optional hdr)         */
  57   unsigned char f_flags[2];     /* flags                        */
  58 };
  59
  60 /* Bits for filehdr f_flags field.  */
  61
  62 #define F_EXEC                  (0x0002)
  63 #define IMAGE_FILE_SYSTEM       (0x1000)
  64 #define IMAGE_FILE_DLL          (0x2000)
  65
  66 /* COFF section header.  */
  67
  68 struct external_scnhdr
  69 {
  70   unsigned char s_name[8];      /* section name                         */
  71   unsigned char s_paddr[4];     /* physical address, aliased s_nlib     */
  72   unsigned char s_vaddr[4];     /* virtual address                      */
  73   unsigned char s_size[4];      /* section size                         */
  74   unsigned char s_scnptr[4];    /* file ptr to raw data for section     */
  75   unsigned char s_relptr[4];    /* file ptr to relocation               */
  76   unsigned char s_lnnoptr[4];   /* file ptr to line numbers             */
  77   unsigned char s_nreloc[2];    /* number of relocation entries         */
  78   unsigned char s_nlnno[2];     /* number of line number entries        */
  79   unsigned char s_flags[4];     /* flags                                */
  80 };
  81
  82 /* The length of the s_name field in struct external_scnhdr.  */
  83
  84 #define SCNNMLEN (8)
  85
  86 /* Bits for scnhdr s_flags field.  This includes some bits defined
  87    only for PE.  This may need to be moved into coff_magic.  */
  88
  89 #define STYP_DATA                       (1 << 6)
  90 #define IMAGE_SCN_MEM_DISCARDABLE       (1 << 25)
  91 #define IMAGE_SCN_MEM_SHARED            (1 << 28)
  92 #define IMAGE_SCN_MEM_READ              (1 << 30)
  93
  94 #define IMAGE_SCN_ALIGN_POWER_BIT_POS        20
  95 #define IMAGE_SCN_ALIGN_POWER_CONST(val)     \
  96   (((val) + 1) << IMAGE_SCN_ALIGN_POWER_BIT_POS)
  97
  98 /* COFF symbol table entry.  */
  99
 100 #define E_SYMNMLEN      8       /* # characters in a symbol name        */
 101
 102 struct external_syment
 103 {
 104   union
 105   {
 106     unsigned char e_name[E_SYMNMLEN];
 107
 108     struct
 109     {
 110       unsigned char e_zeroes[4];
 111       unsigned char e_offset[4];
 112     } e;
 113   } e;
 114
 115   unsigned char e_value[4];
 116   unsigned char e_scnum[2];
 117   unsigned char e_type[2];
 118   unsigned char e_sclass[1];
 119   unsigned char e_numaux[1];
 120 };
 121
 122 /* Length allowed for filename in aux sym format 4.  */
 123
 124 #define E_FILNMLEN      18
 125
 126 /* Omits x_sym and other unused variants.  */
 127
 128 union external_auxent
 129 {
 130   /* Aux sym format 4: file.  */
 131   union
 132   {
 133     char x_fname[E_FILNMLEN];
 134     struct
 135     {
 136       unsigned char x_zeroes[4];
 137       unsigned char x_offset[4];
 138     } x_n;
 139   } x_file;
 140   /* Aux sym format 5: section.  */
 141   struct
 142   {
 143     unsigned char x_scnlen[4];          /* section length               */
 144     unsigned char x_nreloc[2];          /* # relocation entries         */
 145     unsigned char x_nlinno[2];          /* # line numbers               */
 146     unsigned char x_checksum[4];        /* section COMDAT checksum      */
 147     unsigned char x_associated[2];      /* COMDAT assoc section index   */
 148     unsigned char x_comdat[1];          /* COMDAT selection number      */
 149   } x_scn;
 150 };
 151
 152 /* Symbol-related constants.  */
 153
 154 #define IMAGE_SYM_DEBUG         (-2)
 155 #define IMAGE_SYM_TYPE_NULL     (0)
 156 #define IMAGE_SYM_DTYPE_NULL    (0)
 157 #define IMAGE_SYM_CLASS_STATIC  (3)
 158 #define IMAGE_SYM_CLASS_FILE    (103)
 159
 160 #define IMAGE_SYM_TYPE \
 161   ((IMAGE_SYM_DTYPE_NULL << 4) | IMAGE_SYM_TYPE_NULL)
 162
 163 /* Private data for an simple_object_read.  */
 164
 165 struct simple_object_coff_read
 166 {
 167   /* Magic number.  */
 168   unsigned short magic;
 169   /* Whether the file is big-endian.  */
 170   unsigned char is_big_endian;
 171   /* Number of sections.  */
 172   unsigned short nscns;
 173   /* File offset of symbol table.  */
 174   off_t symptr;
 175   /* Number of symbol table entries.  */
 176   unsigned int nsyms;
 177   /* Flags.  */
 178   unsigned short flags;
 179   /* Offset of section headers in file.  */
 180   off_t scnhdr_offset;
 181 };
 182
 183 /* Private data for an simple_object_attributes.  */
 184
 185 struct simple_object_coff_attributes
 186 {
 187   /* Magic number.  */
 188   unsigned short magic;
 189   /* Whether the file is big-endian.  */
 190   unsigned char is_big_endian;
 191   /* Flags.  */
 192   unsigned short flags;
 193 };
 194
 195 /* There is no magic number which indicates a COFF file as opposed to
 196    any other sort of file.  Instead, each COFF file starts with a
 197    two-byte magic number which also indicates the type of the target.
 198    This struct holds a magic number as well as characteristics of that
 199    COFF format.  */
 200
 201 struct coff_magic_struct
 202 {
 203   /* Magic number.  */
 204   unsigned short magic;
 205   /* Whether this magic number is for a big-endian file.  */
 206   unsigned char is_big_endian;
 207   /* Flag bits, in the f_flags fields, which indicates that this file
 208      is not a relocatable object file.  There is no flag which
 209      specifically indicates a relocatable object file, it is only
 210      implied by the absence of these flags.  */
 211   unsigned short non_object_flags;
 212 };
 213
 214 /* This is a list of the COFF magic numbers which we recognize, namely
 215    the ones used on Windows.  More can be added as needed.  */
 216
 217 static const struct coff_magic_struct coff_magic[] =
 218 {
 219   /* i386.  */
 220   { 0x14c, 0, F_EXEC | IMAGE_FILE_SYSTEM | IMAGE_FILE_DLL },
 221   /* x86_64.  */
 222   { 0x8664, 0, F_EXEC | IMAGE_FILE_SYSTEM | IMAGE_FILE_DLL }
 223 };
 224
 225 /* See if we have a COFF file.  */
 226
 227 static void *
 228 simple_object_coff_match (unsigned char header[SIMPLE_OBJECT_MATCH_HEADER_LEN],
 229                           int descriptor, off_t offset,
 230                           const char *segment_name ATTRIBUTE_UNUSED,
 231                           const char **errmsg, int *err)
 232 {
 233   size_t c;
 234   unsigned short magic_big;
 235   unsigned short magic_little;
 236   unsigned short magic;
 237   size_t i;
 238   int is_big_endian;
 239   unsigned short (*fetch_16) (const unsigned char *);
 240   unsigned int (*fetch_32) (const unsigned char *);
 241   unsigned char hdrbuf[sizeof (struct external_filehdr)];
 242   unsigned short flags;
 243   struct simple_object_coff_read *ocr;
 244
 245   c = sizeof (coff_magic) / sizeof (coff_magic[0]);
 246   magic_big = simple_object_fetch_big_16 (header);
 247   magic_little = simple_object_fetch_little_16 (header);
 248   for (i = 0; i < c; ++i)
 249     {
 250       if (coff_magic[i].is_big_endian
 251           ? coff_magic[i].magic == magic_big
 252           : coff_magic[i].magic == magic_little)
 253         break;
 254     }
 255   if (i >= c)
 256     {
 257       *errmsg = NULL;
 258       *err = 0;
 259       return NULL;
 260     }
 261   is_big_endian = coff_magic[i].is_big_endian;
 262
 263   magic = is_big_endian ? magic_big : magic_little;
 264   fetch_16 = (is_big_endian
 265               ? simple_object_fetch_big_16
 266               : simple_object_fetch_little_16);
 267   fetch_32 = (is_big_endian
 268               ? simple_object_fetch_big_32
 269               : simple_object_fetch_little_32);
 270
 271   if (!simple_object_internal_read (descriptor, offset, hdrbuf, sizeof hdrbuf,
 272                                     errmsg, err))
 273     return NULL;
 274
 275   flags = fetch_16 (hdrbuf + offsetof (struct external_filehdr, f_flags));
 276   if ((flags & coff_magic[i].non_object_flags) != 0)
 277     {
 278       *errmsg = "not relocatable object file";
 279       *err = 0;
 280       return NULL;
 281     }
 282
 283   ocr = XNEW (struct simple_object_coff_read);
 284   ocr->magic = magic;
 285   ocr->is_big_endian = is_big_endian;
 286   ocr->nscns = fetch_16 (hdrbuf + offsetof (struct external_filehdr, f_nscns));
 287   ocr->symptr = fetch_32 (hdrbuf
 288                           + offsetof (struct external_filehdr, f_symptr));
 289   ocr->nsyms = fetch_32 (hdrbuf + offsetof (struct external_filehdr, f_nsyms));
 290   ocr->flags = flags;
 291   ocr->scnhdr_offset = (sizeof (struct external_filehdr)
 292                         + fetch_16 (hdrbuf + offsetof (struct external_filehdr,
 293                                                        f_opthdr)));
 294
 295   return (void *) ocr;
 296 }
 297
 298 /* Read the string table in a COFF file.  */
 299
 300 static char *
 301 simple_object_coff_read_strtab (simple_object_read *sobj, size_t *strtab_size,
 302                                 const char **errmsg, int *err)
 303 {
 304   struct simple_object_coff_read *ocr =
 305     (struct simple_object_coff_read *) sobj->data;
 306   off_t strtab_offset;
 307   unsigned char strsizebuf[4];
 308   size_t strsize;
 309   char *strtab;
 310
 311   strtab_offset = sobj->offset + ocr->symptr
 312                   + ocr->nsyms * sizeof (struct external_syment);
 313   if (!simple_object_internal_read (sobj->descriptor, strtab_offset,
 314                                     strsizebuf, 4, errmsg, err))
 315     return NULL;
 316   strsize = (ocr->is_big_endian
 317              ? simple_object_fetch_big_32 (strsizebuf)
 318              : simple_object_fetch_little_32 (strsizebuf));
 319   strtab = XNEWVEC (char, strsize);
 320   if (!simple_object_internal_read (sobj->descriptor, strtab_offset,
 321                                     (unsigned char *) strtab, strsize, errmsg,
 322                                     err))
 323     {
 324       XDELETEVEC (strtab);
 325       return NULL;
 326     }
 327   *strtab_size = strsize;
 328   return strtab;
 329 }
 330
 331 /* Find all sections in a COFF file.  */
 332
 333 static const char *
 334 simple_object_coff_find_sections (simple_object_read *sobj,
 335                                   int (*pfn) (void *, const char *,
 336                                               off_t offset, off_t length),
 337                                   void *data,
 338                                   int *err)
 339 {
 340   struct simple_object_coff_read *ocr =
 341     (struct simple_object_coff_read *) sobj->data;
 342   size_t scnhdr_size;
 343   unsigned char *scnbuf;
 344   const char *errmsg;
 345   unsigned int (*fetch_32) (const unsigned char *);
 346   unsigned int nscns;
 347   char *strtab;
 348   size_t strtab_size;
 349   unsigned int i;
 350
 351   scnhdr_size = sizeof (struct external_scnhdr);
 352   scnbuf = XNEWVEC (unsigned char, scnhdr_size * ocr->nscns);
 353   if (!simple_object_internal_read (sobj->descriptor,
 354                                     sobj->offset + ocr->scnhdr_offset,
 355                                     scnbuf, scnhdr_size * ocr->nscns, &errmsg,
 356                                     err))
 357     {
 358       XDELETEVEC (scnbuf);
 359       return errmsg;
 360     }
 361
 362   fetch_32 = (ocr->is_big_endian
 363               ? simple_object_fetch_big_32
 364               : simple_object_fetch_little_32);
 365
 366   nscns = ocr->nscns;
 367   strtab = NULL;
 368   strtab_size = 0;
 369   for (i = 0; i < nscns; ++i)
 370     {
 371       unsigned char *scnhdr;
 372       unsigned char *scnname;
 373       char namebuf[SCNNMLEN + 1];
 374       char *name;
 375       off_t scnptr;
 376       unsigned int size;
 377
 378       scnhdr = scnbuf + i * scnhdr_size;
 379       scnname = scnhdr + offsetof (struct external_scnhdr, s_name);
 380       memcpy (namebuf, scnname, SCNNMLEN);
 381       namebuf[SCNNMLEN] = '\0';
 382       name = &namebuf[0];
 383       if (namebuf[0] == '/')
 384         {
 385           size_t strindex;
 386           char *end;
 387
 388           strindex = strtol (namebuf + 1, &end, 10);
 389           if (*end == '\0')
 390             {
 391               /* The real section name is found in the string
 392                  table.  */
 393               if (strtab == NULL)
 394                 {
 395                   strtab = simple_object_coff_read_strtab (sobj,
 396                                                            &strtab_size,
 397                                                            &errmsg, err);
 398                   if (strtab == NULL)
 399                     {
 400                       XDELETEVEC (scnbuf);
 401                       return errmsg;
 402                     }
 403                 }
 404
 405               if (strindex < 4 || strindex >= strtab_size)
 406                 {
 407                   XDELETEVEC (strtab);
 408                   XDELETEVEC (scnbuf);
 409                   *err = 0;
 410                   return "section string index out of range";
 411                 }
 412
 413               name = strtab + strindex;
 414             }
 415         }
 416
 417       scnptr = fetch_32 (scnhdr + offsetof (struct external_scnhdr, s_scnptr));
 418       size = fetch_32 (scnhdr + offsetof (struct external_scnhdr, s_size));
 419
 420       if (!(*pfn) (data, name, scnptr, size))
 421         break;
 422     }
 423
 424   if (strtab != NULL)
 425     XDELETEVEC (strtab);
 426   XDELETEVEC (scnbuf);
 427
 428   return NULL;
 429 }
 430
 431 /* Fetch the attributes for an simple_object_read.  */
 432
 433 static void *
 434 simple_object_coff_fetch_attributes (simple_object_read *sobj,
 435                                      const char **errmsg ATTRIBUTE_UNUSED,
 436                                      int *err ATTRIBUTE_UNUSED)
 437 {
 438   struct simple_object_coff_read *ocr =
 439     (struct simple_object_coff_read *) sobj->data;
 440   struct simple_object_coff_attributes *ret;
 441
 442   ret = XNEW (struct simple_object_coff_attributes);
 443   ret->magic = ocr->magic;
 444   ret->is_big_endian = ocr->is_big_endian;
 445   ret->flags = ocr->flags;
 446   return ret;
 447 }
 448
 449 /* Release the private data for an simple_object_read.  */
 450
 451 static void
 452 simple_object_coff_release_read (void *data)
 453 {
 454   XDELETE (data);
 455 }
 456
 457 /* Compare two attributes structures.  */
 458
 459 static const char *
 460 simple_object_coff_attributes_merge (void *todata, void *fromdata, int *err)
 461 {
 462   struct simple_object_coff_attributes *to =
 463     (struct simple_object_coff_attributes *) todata;
 464   struct simple_object_coff_attributes *from =
 465     (struct simple_object_coff_attributes *) fromdata;
 466
 467   if (to->magic != from->magic || to->is_big_endian != from->is_big_endian)
 468     {
 469       *err = 0;
 470       return "COFF object format mismatch";
 471     }
 472   return NULL;
 473 }
 474
 475 /* Release the private data for an attributes structure.  */
 476
 477 static void
 478 simple_object_coff_release_attributes (void *data)
 479 {
 480   XDELETE (data);
 481 }
 482
 483 /* Prepare to write out a file.  */
 484
 485 static void *
 486 simple_object_coff_start_write (void *attributes_data,
 487                                 const char **errmsg ATTRIBUTE_UNUSED,
 488                                 int *err ATTRIBUTE_UNUSED)
 489 {
 490   struct simple_object_coff_attributes *attrs =
 491     (struct simple_object_coff_attributes *) attributes_data;
 492   struct simple_object_coff_attributes *ret;
 493
 494   /* We're just going to record the attributes, but we need to make a
 495      copy because the user may delete them.  */
 496   ret = XNEW (struct simple_object_coff_attributes);
 497   *ret = *attrs;
 498   return ret;
 499 }
 500
 501 /* Write out a COFF filehdr.  */
 502
 503 static int
 504 simple_object_coff_write_filehdr (simple_object_write *sobj, int descriptor,
 505                                   unsigned int nscns, size_t symtab_offset,
 506                                   unsigned int nsyms, const char **errmsg,
 507                                   int *err)
 508 {
 509   struct simple_object_coff_attributes *attrs =
 510     (struct simple_object_coff_attributes *) sobj->data;
 511   unsigned char hdrbuf[sizeof (struct external_filehdr)];
 512   unsigned char *hdr;
 513   void (*set_16) (unsigned char *, unsigned short);
 514   void (*set_32) (unsigned char *, unsigned int);
 515
 516   hdr = &hdrbuf[0];
 517
 518   set_16 = (attrs->is_big_endian
 519             ? simple_object_set_big_16
 520             : simple_object_set_little_16);
 521   set_32 = (attrs->is_big_endian
 522             ? simple_object_set_big_32
 523             : simple_object_set_little_32);
 524
 525   memset (hdr, 0, sizeof (struct external_filehdr));
 526
 527   set_16 (hdr + offsetof (struct external_filehdr, f_magic), attrs->magic);
 528   set_16 (hdr + offsetof (struct external_filehdr, f_nscns), nscns);
 529   /* f_timdat left as zero.  */
 530   set_32 (hdr + offsetof (struct external_filehdr, f_symptr), symtab_offset);
 531   set_32 (hdr + offsetof (struct external_filehdr, f_nsyms), nsyms);
 532   /* f_opthdr left as zero.  */
 533   set_16 (hdr + offsetof (struct external_filehdr, f_flags), attrs->flags);
 534
 535   return simple_object_internal_write (descriptor, 0, hdrbuf,
 536                                        sizeof (struct external_filehdr),
 537                                        errmsg, err);
 538 }
 539
 540 /* Write out a COFF section header.  */
 541
 542 static int
 543 simple_object_coff_write_scnhdr (simple_object_write *sobj, int descriptor,
 544                                  const char *name, size_t *name_offset,
 545                                  off_t scnhdr_offset, size_t scnsize,
 546                                  off_t offset, unsigned int align,
 547                                  const char **errmsg, int *err)
 548 {
 549   struct simple_object_coff_attributes *attrs =
 550     (struct simple_object_coff_attributes *) sobj->data;
 551   void (*set_32) (unsigned char *, unsigned int);
 552   unsigned char hdrbuf[sizeof (struct external_scnhdr)];
 553   unsigned char *hdr;
 554   size_t namelen;
 555   unsigned int flags;
 556
 557   set_32 = (attrs->is_big_endian
 558             ? simple_object_set_big_32
 559             : simple_object_set_little_32);
 560
 561   memset (hdrbuf, 0, sizeof hdrbuf);
 562   hdr = &hdrbuf[0];
 563
 564   namelen = strlen (name);
 565   if (namelen <= SCNNMLEN)
 566     strncpy ((char *) hdr + offsetof (struct external_scnhdr, s_name), name,
 567              SCNNMLEN);
 568   else
 569     {
 570       snprintf ((char *) hdr + offsetof (struct external_scnhdr, s_name),
 571                 SCNNMLEN, "/%lu", (unsigned long) *name_offset);
 572       *name_offset += namelen + 1;
 573     }
 574
 575   /* s_paddr left as zero.  */
 576   /* s_vaddr left as zero.  */
 577   set_32 (hdr + offsetof (struct external_scnhdr, s_size), scnsize);
 578   set_32 (hdr + offsetof (struct external_scnhdr, s_scnptr), offset);
 579   /* s_relptr left as zero.  */
 580   /* s_lnnoptr left as zero.  */
 581   /* s_nreloc left as zero.  */
 582   /* s_nlnno left as zero.  */
 583   flags = (STYP_DATA | IMAGE_SCN_MEM_DISCARDABLE | IMAGE_SCN_MEM_SHARED
 584            | IMAGE_SCN_MEM_READ);
 585   /* PE can represent alignment up to 13.  */
 586   if (align > 13)
 587     align = 13;
 588   flags |= IMAGE_SCN_ALIGN_POWER_CONST(align);
 589   set_32 (hdr + offsetof (struct external_scnhdr, s_flags), flags);
 590
 591   return simple_object_internal_write (descriptor, scnhdr_offset, hdrbuf,
 592                                        sizeof (struct external_scnhdr),
 593                                        errmsg, err);
 594 }
 595
 596 /* Write out a complete COFF file.  */
 597
 598 static const char *
 599 simple_object_coff_write_to_file (simple_object_write *sobj, int descriptor,
 600                                   int *err)
 601 {
 602   struct simple_object_coff_attributes *attrs =
 603     (struct simple_object_coff_attributes *) sobj->data;
 604   unsigned int nscns, secnum;
 605   simple_object_write_section *section;
 606   off_t scnhdr_offset;
 607   size_t symtab_offset;
 608   off_t secsym_offset;
 609   unsigned int nsyms;
 610   size_t offset;
 611   size_t name_offset;
 612   const char *errmsg;
 613   unsigned char strsizebuf[4];
 614   /* The interface doesn't give us access to the name of the input file
 615      yet.  We want to use its basename for the FILE symbol.  This is
 616      what 'gas' uses when told to assemble from stdin.  */
 617   const char *source_filename = "fake";
 618   size_t sflen;
 619   union
 620   {
 621     struct external_syment sym;
 622     union external_auxent aux;
 623   } syms[2];
 624   void (*set_16) (unsigned char *, unsigned short);
 625   void (*set_32) (unsigned char *, unsigned int);
 626
 627   set_16 = (attrs->is_big_endian
 628             ? simple_object_set_big_16
 629             : simple_object_set_little_16);
 630   set_32 = (attrs->is_big_endian
 631             ? simple_object_set_big_32
 632             : simple_object_set_little_32);
 633
 634   nscns = 0;
 635   for (section = sobj->sections; section != NULL; section = section->next)
 636     ++nscns;
 637
 638   scnhdr_offset = sizeof (struct external_filehdr);
 639   offset = scnhdr_offset + nscns * sizeof (struct external_scnhdr);
 640   name_offset = 4;
 641   for (section = sobj->sections; section != NULL; section = section->next)
 642     {
 643       size_t mask;
 644       size_t new_offset;
 645       size_t scnsize;
 646       struct simple_object_write_section_buffer *buffer;
 647
 648       mask = (1U << section->align) - 1;
 649       new_offset = offset & mask;
 650       new_offset &= ~ mask;
 651       while (new_offset > offset)
 652         {
 653           unsigned char zeroes[16];
 654           size_t write;
 655
 656           memset (zeroes, 0, sizeof zeroes);
 657           write = new_offset - offset;
 658           if (write > sizeof zeroes)
 659             write = sizeof zeroes;
 660           if (!simple_object_internal_write (descriptor, offset, zeroes, write,
 661                                              &errmsg, err))
 662             return errmsg;
 663         }
 664
 665       scnsize = 0;
 666       for (buffer = section->buffers; buffer != NULL; buffer = buffer->next)
 667         {
 668           if (!simple_object_internal_write (descriptor, offset + scnsize,
 669                                              ((const unsigned char *)
 670                                               buffer->buffer),
 671                                              buffer->size, &errmsg, err))
 672             return errmsg;
 673           scnsize += buffer->size;
 674         }
 675
 676       if (!simple_object_coff_write_scnhdr (sobj, descriptor, section->name,
 677                                             &name_offset, scnhdr_offset,
 678                                             scnsize, offset, section->align,
 679                                             &errmsg, err))
 680         return errmsg;
 681
 682       scnhdr_offset += sizeof (struct external_scnhdr);
 683       offset += scnsize;
 684     }
 685
 686   /* Symbol table is always half-word aligned.  */
 687   offset += (offset & 1);
 688   /* There is a file symbol and a section symbol per section,
 689      and each of these has a single auxiliary symbol following.  */
 690   nsyms = 2 * (nscns + 1);
 691   symtab_offset = offset;
 692   /* Advance across space reserved for symbol table to locate
 693      start of string table.  */
 694   offset += nsyms * sizeof (struct external_syment);
 695
 696   /* Write out file symbol.  */
 697   memset (&syms[0], 0, sizeof (syms));
 698   strcpy ((char *)&syms[0].sym.e.e_name[0], ".file");
 699   set_16 (&syms[0].sym.e_scnum[0], IMAGE_SYM_DEBUG);
 700   set_16 (&syms[0].sym.e_type[0], IMAGE_SYM_TYPE);
 701   syms[0].sym.e_sclass[0] = IMAGE_SYM_CLASS_FILE;
 702   syms[0].sym.e_numaux[0] = 1;
 703   /* The name need not be nul-terminated if it fits into the x_fname field
 704      directly, but must be if it has to be placed into the string table.  */
 705   sflen = strlen (source_filename);
 706   if (sflen <= E_FILNMLEN)
 707     memcpy (&syms[1].aux.x_file.x_fname[0], source_filename, sflen);
 708   else
 709     {
 710       set_32 (&syms[1].aux.x_file.x_n.x_offset[0], name_offset);
 711       if (!simple_object_internal_write (descriptor, offset + name_offset,
 712                                          ((const unsigned char *)
 713                                           source_filename),
 714                                          sflen + 1, &errmsg, err))
 715         return errmsg;
 716       name_offset += strlen (source_filename) + 1;
 717     }
 718   if (!simple_object_internal_write (descriptor, symtab_offset,
 719                                      (const unsigned char *) &syms[0],
 720                                      sizeof (syms), &errmsg, err))
 721     return errmsg;
 722
 723   /* Write the string table length, followed by the strings and section
 724      symbols in step with each other.  */
 725   set_32 (strsizebuf, name_offset);
 726   if (!simple_object_internal_write (descriptor, offset, strsizebuf, 4,
 727                                      &errmsg, err))
 728     return errmsg;
 729
 730   name_offset = 4;
 731   secsym_offset = symtab_offset + sizeof (syms);
 732   memset (&syms[0], 0, sizeof (syms));
 733   set_16 (&syms[0].sym.e_type[0], IMAGE_SYM_TYPE);
 734   syms[0].sym.e_sclass[0] = IMAGE_SYM_CLASS_STATIC;
 735   syms[0].sym.e_numaux[0] = 1;
 736   secnum = 1;
 737
 738   for (section = sobj->sections; section != NULL; section = section->next)
 739     {
 740       size_t namelen;
 741       size_t scnsize;
 742       struct simple_object_write_section_buffer *buffer;
 743
 744       namelen = strlen (section->name);
 745       set_16 (&syms[0].sym.e_scnum[0], secnum++);
 746       scnsize = 0;
 747       for (buffer = section->buffers; buffer != NULL; buffer = buffer->next)
 748         scnsize += buffer->size;
 749       set_32 (&syms[1].aux.x_scn.x_scnlen[0], scnsize);
 750       if (namelen > SCNNMLEN)
 751         {
 752           set_32 (&syms[0].sym.e.e.e_zeroes[0], 0);
 753           set_32 (&syms[0].sym.e.e.e_offset[0], name_offset);
 754           if (!simple_object_internal_write (descriptor, offset + name_offset,
 755                                              ((const unsigned char *)
 756                                               section->name),
 757                                              namelen + 1, &errmsg, err))
 758             return errmsg;
 759           name_offset += namelen + 1;
 760         }
 761       else
 762         {
 763           memcpy (&syms[0].sym.e.e_name[0], section->name,
 764                   strlen (section->name));
 765           memset (&syms[0].sym.e.e_name[strlen (section->name)], 0,
 766                   E_SYMNMLEN - strlen (section->name));
 767         }
 768
 769       if (!simple_object_internal_write (descriptor, secsym_offset,
 770                                          (const unsigned char *) &syms[0],
 771                                          sizeof (syms), &errmsg, err))
 772         return errmsg;
 773       secsym_offset += sizeof (syms);
 774     }
 775
 776   if (!simple_object_coff_write_filehdr (sobj, descriptor, nscns,
 777                                          symtab_offset, nsyms, &errmsg, err))
 778     return errmsg;
 779
 780   return NULL;
 781 }
 782
 783 /* Release the private data for an simple_object_write structure.  */
 784
 785 static void
 786 simple_object_coff_release_write (void *data)
 787 {
 788   XDELETE (data);
 789 }
 790
 791 /* The COFF functions.  */
 792
 793 const struct simple_object_functions simple_object_coff_functions =
 794 {
 795   simple_object_coff_match,
 796   simple_object_coff_find_sections,
 797   simple_object_coff_fetch_attributes,
 798   simple_object_coff_release_read,
 799   simple_object_coff_attributes_merge,
 800   simple_object_coff_release_attributes,
 801   simple_object_coff_start_write,
 802   simple_object_coff_write_to_file,
 803   simple_object_coff_release_write,
 804   NULL
 805 };