bfd/cache.c

   1 /* BFD library -- caching of file descriptors.
   2
   3    Copyright 1990, 1991, 1992, 1993, 1994, 1996, 2000, 2001, 2002,
   4    2003, 2004, 2005, 2007 Free Software Foundation, Inc.
   5
   6    Hacked by Steve Chamberlain of Cygnus Support (steve@cygnus.com).
   7
   8    This file is part of BFD, the Binary File Descriptor library.
   9
  10    This program is free software; you can redistribute it and/or modify
  11    it under the terms of the GNU General Public License as published by
  12    the Free Software Foundation; either version 3 of the License, or
  13    (at your option) any later version.
  14
  15    This program is distributed in the hope that it will be useful,
  16    but WITHOUT ANY WARRANTY; without even the implied warranty of
  17    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  18    GNU General Public License for more details.
  19
  20    You should have received a copy of the GNU General Public License
  21    along with this program; if not, write to the Free Software
  22    Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
  23    MA 02110-1301, USA.  */
  24
  25 /*
  26 SECTION
  27         File caching
  28
  29         The file caching mechanism is embedded within BFD and allows
  30         the application to open as many BFDs as it wants without
  31         regard to the underlying operating system's file descriptor
  32         limit (often as low as 20 open files).  The module in
  33         <<cache.c>> maintains a least recently used list of
  34         <<BFD_CACHE_MAX_OPEN>> files, and exports the name
  35         <<bfd_cache_lookup>>, which runs around and makes sure that
  36         the required BFD is open. If not, then it chooses a file to
  37         close, closes it and opens the one wanted, returning its file
  38         handle.
  39
  40 SUBSECTION
  41         Caching functions
  42 */
  43
  44 #include "sysdep.h"
  45 #include "bfd.h"
  46 #include "libbfd.h"
  47 #include "libiberty.h"
  48
  49 /* In some cases we can optimize cache operation when reopening files.
  50    For instance, a flush is entirely unnecessary if the file is already
  51    closed, so a flush would use CACHE_NO_OPEN.  Similarly, a seek using
  52    SEEK_SET or SEEK_END need not first seek to the current position.
  53    For stat we ignore seek errors, just in case the file has changed
  54    while we weren't looking.  If it has, then it's possible that the
  55    file is shorter and we don't want a seek error to prevent us doing
  56    the stat.  */
  57 enum cache_flag {
  58   CACHE_NORMAL = 0,
  59   CACHE_NO_OPEN = 1,
  60   CACHE_NO_SEEK = 2,
  61   CACHE_NO_SEEK_ERROR = 4
  62 };
  63
  64 /* The maximum number of files which the cache will keep open at
  65    one time.  */
  66
  67 #define BFD_CACHE_MAX_OPEN 10
  68
  69 /* The number of BFD files we have open.  */
  70
  71 static int open_files;
  72
  73 /* Zero, or a pointer to the topmost BFD on the chain.  This is
  74    used by the <<bfd_cache_lookup>> macro in @file{libbfd.h} to
  75    determine when it can avoid a function call.  */
  76
  77 static bfd *bfd_last_cache = NULL;
  78
  79 /* Insert a BFD into the cache.  */
  80
  81 static void
  82 insert (bfd *abfd)
  83 {
  84   if (bfd_last_cache == NULL)
  85     {
  86       abfd->lru_next = abfd;
  87       abfd->lru_prev = abfd;
  88     }
  89   else
  90     {
  91       abfd->lru_next = bfd_last_cache;
  92       abfd->lru_prev = bfd_last_cache->lru_prev;
  93       abfd->lru_prev->lru_next = abfd;
  94       abfd->lru_next->lru_prev = abfd;
  95     }
  96   bfd_last_cache = abfd;
  97 }
  98
  99 /* Remove a BFD from the cache.  */
 100
 101 static void
 102 snip (bfd *abfd)
 103 {
 104   abfd->lru_prev->lru_next = abfd->lru_next;
 105   abfd->lru_next->lru_prev = abfd->lru_prev;
 106   if (abfd == bfd_last_cache)
 107     {
 108       bfd_last_cache = abfd->lru_next;
 109       if (abfd == bfd_last_cache)
 110         bfd_last_cache = NULL;
 111     }
 112 }
 113
 114 /* Close a BFD and remove it from the cache.  */
 115
 116 static bfd_boolean
 117 bfd_cache_delete (bfd *abfd)
 118 {
 119   bfd_boolean ret;
 120
 121   if (fclose ((FILE *) abfd->iostream) == 0)
 122     ret = TRUE;
 123   else
 124     {
 125       ret = FALSE;
 126       bfd_set_error (bfd_error_system_call);
 127     }
 128
 129   snip (abfd);
 130
 131   abfd->iostream = NULL;
 132   --open_files;
 133
 134   return ret;
 135 }
 136
 137 /* We need to open a new file, and the cache is full.  Find the least
 138    recently used cacheable BFD and close it.  */
 139
 140 static bfd_boolean
 141 close_one (void)
 142 {
 143   register bfd *kill;
 144
 145   if (bfd_last_cache == NULL)
 146     kill = NULL;
 147   else
 148     {
 149       for (kill = bfd_last_cache->lru_prev;
 150            ! kill->cacheable;
 151            kill = kill->lru_prev)
 152         {
 153           if (kill == bfd_last_cache)
 154             {
 155               kill = NULL;
 156               break;
 157             }
 158         }
 159     }
 160
 161   if (kill == NULL)
 162     {
 163       /* There are no open cacheable BFD's.  */
 164       return TRUE;
 165     }
 166
 167   kill->where = real_ftell ((FILE *) kill->iostream);
 168
 169   return bfd_cache_delete (kill);
 170 }
 171
 172 /* Check to see if the required BFD is the same as the last one
 173    looked up. If so, then it can use the stream in the BFD with
 174    impunity, since it can't have changed since the last lookup;
 175    otherwise, it has to perform the complicated lookup function.  */
 176
 177 #define bfd_cache_lookup(x, flag) \
 178   ((x) == bfd_last_cache                        \
 179    ? (FILE *) (bfd_last_cache->iostream)        \
 180    : bfd_cache_lookup_worker (x, flag))
 181
 182 /* Called when the macro <<bfd_cache_lookup>> fails to find a
 183    quick answer.  Find a file descriptor for @var{abfd}.  If
 184    necessary, it open it.  If there are already more than
 185    <<BFD_CACHE_MAX_OPEN>> files open, it tries to close one first, to
 186    avoid running out of file descriptors.  It will return NULL
 187    if it is unable to (re)open the @var{abfd}.  */
 188
 189 static FILE *
 190 bfd_cache_lookup_worker (bfd *abfd, enum cache_flag flag)
 191 {
 192   bfd *orig_bfd = abfd;
 193   if ((abfd->flags & BFD_IN_MEMORY) != 0)
 194     abort ();
 195
 196   if (abfd->my_archive)
 197     abfd = abfd->my_archive;
 198
 199   if (abfd->iostream != NULL)
 200     {
 201       /* Move the file to the start of the cache.  */
 202       if (abfd != bfd_last_cache)
 203         {
 204           snip (abfd);
 205           insert (abfd);
 206         }
 207       return (FILE *) abfd->iostream;
 208     }
 209
 210   if (flag & CACHE_NO_OPEN)
 211     return NULL;
 212
 213   if (bfd_open_file (abfd) == NULL)
 214     ;
 215   else if (!(flag & CACHE_NO_SEEK)
 216            && real_fseek ((FILE *) abfd->iostream, abfd->where, SEEK_SET) != 0
 217            && !(flag & CACHE_NO_SEEK_ERROR))
 218     bfd_set_error (bfd_error_system_call);
 219   else
 220     return (FILE *) abfd->iostream;
 221
 222   (*_bfd_error_handler) (_("reopening %B: %s\n"),
 223                          orig_bfd, bfd_errmsg (bfd_get_error ()));
 224   return NULL;
 225 }
 226
 227 static file_ptr
 228 cache_btell (struct bfd *abfd)
 229 {
 230   FILE *f = bfd_cache_lookup (abfd, CACHE_NO_OPEN);
 231   if (f == NULL)
 232     return abfd->where;
 233   return real_ftell (f);
 234 }
 235
 236 static int
 237 cache_bseek (struct bfd *abfd, file_ptr offset, int whence)
 238 {
 239   FILE *f = bfd_cache_lookup (abfd, whence != SEEK_CUR ? CACHE_NO_SEEK : 0);
 240   if (f == NULL)
 241     return -1;
 242   return real_fseek (f, offset, whence);
 243 }
 244
 245 /* Note that archive entries don't have streams; they share their parent's.
 246    This allows someone to play with the iostream behind BFD's back.
 247
 248    Also, note that the origin pointer points to the beginning of a file's
 249    contents (0 for non-archive elements).  For archive entries this is the
 250    first octet in the file, NOT the beginning of the archive header.  */
 251
 252 static file_ptr
 253 cache_bread (struct bfd *abfd, void *buf, file_ptr nbytes)
 254 {
 255   FILE *f;
 256   file_ptr nread;
 257   /* FIXME - this looks like an optimization, but it's really to cover
 258      up for a feature of some OSs (not solaris - sigh) that
 259      ld/pe-dll.c takes advantage of (apparently) when it creates BFDs
 260      internally and tries to link against them.  BFD seems to be smart
 261      enough to realize there are no symbol records in the "file" that
 262      doesn't exist but attempts to read them anyway.  On Solaris,
 263      attempting to read zero bytes from a NULL file results in a core
 264      dump, but on other platforms it just returns zero bytes read.
 265      This makes it to something reasonable. - DJ */
 266   if (nbytes == 0)
 267     return 0;
 268
 269   f = bfd_cache_lookup (abfd, 0);
 270   if (f == NULL)
 271     return 0;
 272
 273 #if defined (__VAX) && defined (VMS)
 274   /* Apparently fread on Vax VMS does not keep the record length
 275      information.  */
 276   nread = read (fileno (f), buf, nbytes);
 277   /* Set bfd_error if we did not read as much data as we expected.  If
 278      the read failed due to an error set the bfd_error_system_call,
 279      else set bfd_error_file_truncated.  */
 280   if (nread == (file_ptr)-1)
 281     {
 282       bfd_set_error (bfd_error_system_call);
 283       return -1;
 284     }
 285 #else
 286   nread = fread (buf, 1, nbytes, f);
 287   /* Set bfd_error if we did not read as much data as we expected.  If
 288      the read failed due to an error set the bfd_error_system_call,
 289      else set bfd_error_file_truncated.  */
 290   if (nread < nbytes && ferror (f))
 291     {
 292       bfd_set_error (bfd_error_system_call);
 293       return -1;
 294     }
 295 #endif
 296   if (nread < nbytes)
 297     /* This may or may not be an error, but in case the calling code
 298        bails out because of it, set the right error code.  */
 299     bfd_set_error (bfd_error_file_truncated);
 300   return nread;
 301 }
 302
 303 static file_ptr
 304 cache_bwrite (struct bfd *abfd, const void *where, file_ptr nbytes)
 305 {
 306   file_ptr nwrite;
 307   FILE *f = bfd_cache_lookup (abfd, 0);
 308   if (f == NULL)
 309     return 0;
 310   nwrite = fwrite (where, 1, nbytes, f);
 311   if (nwrite < nbytes && ferror (f))
 312     {
 313       bfd_set_error (bfd_error_system_call);
 314       return -1;
 315     }
 316   return nwrite;
 317 }
 318
 319 static int
 320 cache_bclose (struct bfd *abfd)
 321 {
 322   return bfd_cache_close (abfd);
 323 }
 324
 325 static int
 326 cache_bflush (struct bfd *abfd)
 327 {
 328   int sts;
 329   FILE *f = bfd_cache_lookup (abfd, CACHE_NO_OPEN);
 330   if (f == NULL)
 331     return 0;
 332   sts = fflush (f);
 333   if (sts < 0)
 334     bfd_set_error (bfd_error_system_call);
 335   return sts;
 336 }
 337
 338 static int
 339 cache_bstat (struct bfd *abfd, struct stat *sb)
 340 {
 341   int sts;
 342   FILE *f = bfd_cache_lookup (abfd, CACHE_NO_SEEK_ERROR);
 343   if (f == NULL)
 344     return -1;
 345   sts = fstat (fileno (f), sb);
 346   if (sts < 0)
 347     bfd_set_error (bfd_error_system_call);
 348   return sts;
 349 }
 350
 351 static const struct bfd_iovec cache_iovec = {
 352   &cache_bread, &cache_bwrite, &cache_btell, &cache_bseek,
 353   &cache_bclose, &cache_bflush, &cache_bstat
 354 };
 355
 356 /*
 357 INTERNAL_FUNCTION
 358         bfd_cache_init
 359
 360 SYNOPSIS
 361         bfd_boolean bfd_cache_init (bfd *abfd);
 362
 363 DESCRIPTION
 364         Add a newly opened BFD to the cache.
 365 */
 366
 367 bfd_boolean
 368 bfd_cache_init (bfd *abfd)
 369 {
 370   BFD_ASSERT (abfd->iostream != NULL);
 371   if (open_files >= BFD_CACHE_MAX_OPEN)
 372     {
 373       if (! close_one ())
 374         return FALSE;
 375     }
 376   abfd->iovec = &cache_iovec;
 377   insert (abfd);
 378   ++open_files;
 379   return TRUE;
 380 }
 381
 382 /*
 383 INTERNAL_FUNCTION
 384         bfd_cache_close
 385
 386 SYNOPSIS
 387         bfd_boolean bfd_cache_close (bfd *abfd);
 388
 389 DESCRIPTION
 390         Remove the BFD @var{abfd} from the cache. If the attached file is open,
 391         then close it too.
 392
 393 RETURNS
 394         <<FALSE>> is returned if closing the file fails, <<TRUE>> is
 395         returned if all is well.
 396 */
 397
 398 bfd_boolean
 399 bfd_cache_close (bfd *abfd)
 400 {
 401   if (abfd->iovec != &cache_iovec)
 402     return TRUE;
 403
 404   if (abfd->iostream == NULL)
 405     /* Previously closed.  */
 406     return TRUE;
 407
 408   return bfd_cache_delete (abfd);
 409 }
 410
 411 /*
 412 FUNCTION
 413         bfd_cache_close_all
 414
 415 SYNOPSIS
 416         bfd_boolean bfd_cache_close_all (void);
 417
 418 DESCRIPTION
 419         Remove all BFDs from the cache. If the attached file is open,
 420         then close it too.
 421
 422 RETURNS
 423         <<FALSE>> is returned if closing one of the file fails, <<TRUE>> is
 424         returned if all is well.
 425 */
 426
 427 bfd_boolean
 428 bfd_cache_close_all ()
 429 {
 430   bfd_boolean ret = TRUE;
 431
 432   while (bfd_last_cache != NULL)
 433     ret &= bfd_cache_close (bfd_last_cache);
 434
 435   return ret;
 436 }
 437
 438 /*
 439 INTERNAL_FUNCTION
 440         bfd_open_file
 441
 442 SYNOPSIS
 443         FILE* bfd_open_file (bfd *abfd);
 444
 445 DESCRIPTION
 446         Call the OS to open a file for @var{abfd}.  Return the <<FILE *>>
 447         (possibly <<NULL>>) that results from this operation.  Set up the
 448         BFD so that future accesses know the file is open. If the <<FILE *>>
 449         returned is <<NULL>>, then it won't have been put in the
 450         cache, so it won't have to be removed from it.
 451 */
 452
 453 FILE *
 454 bfd_open_file (bfd *abfd)
 455 {
 456   abfd->cacheable = TRUE;       /* Allow it to be closed later.  */
 457
 458   if (open_files >= BFD_CACHE_MAX_OPEN)
 459     {
 460       if (! close_one ())
 461         return NULL;
 462     }
 463
 464   switch (abfd->direction)
 465     {
 466     case read_direction:
 467     case no_direction:
 468       abfd->iostream = (PTR) real_fopen (abfd->filename, FOPEN_RB);
 469       break;
 470     case both_direction:
 471     case write_direction:
 472       if (abfd->opened_once)
 473         {
 474           abfd->iostream = (PTR) real_fopen (abfd->filename, FOPEN_RUB);
 475           if (abfd->iostream == NULL)
 476             abfd->iostream = (PTR) real_fopen (abfd->filename, FOPEN_WUB);
 477         }
 478       else
 479         {
 480           /* Create the file.
 481
 482              Some operating systems won't let us overwrite a running
 483              binary.  For them, we want to unlink the file first.
 484
 485              However, gcc 2.95 will create temporary files using
 486              O_EXCL and tight permissions to prevent other users from
 487              substituting other .o files during the compilation.  gcc
 488              will then tell the assembler to use the newly created
 489              file as an output file.  If we unlink the file here, we
 490              open a brief window when another user could still
 491              substitute a file.
 492
 493              So we unlink the output file if and only if it has
 494              non-zero size.  */
 495 #ifndef __MSDOS__
 496           /* Don't do this for MSDOS: it doesn't care about overwriting
 497              a running binary, but if this file is already open by
 498              another BFD, we will be in deep trouble if we delete an
 499              open file.  In fact, objdump does just that if invoked with
 500              the --info option.  */
 501           struct stat s;
 502
 503           if (stat (abfd->filename, &s) == 0 && s.st_size != 0)
 504             unlink_if_ordinary (abfd->filename);
 505 #endif
 506           abfd->iostream = (PTR) real_fopen (abfd->filename, FOPEN_WUB);
 507           abfd->opened_once = TRUE;
 508         }
 509       break;
 510     }
 511
 512   if (abfd->iostream == NULL)
 513     bfd_set_error (bfd_error_system_call);
 514   else
 515     {
 516       if (! bfd_cache_init (abfd))
 517         return NULL;
 518     }
 519
 520   return (FILE *) abfd->iostream;
 521 }