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_1 (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_bread (struct bfd *abfd, void *buf, file_ptr nbytes)
 305 {
 306   file_ptr nread = 0;
 307
 308   /* Some filesystems are unable to handle reads that are too large
 309      (for instance, NetApp shares with oplocks turned off).  To avoid
 310      hitting this limitation, we read the buffer in chunks of 8MB max.  */
 311   while (nread < nbytes)
 312     {
 313       const file_ptr max_chunk_size = 0x800000;
 314       file_ptr chunk_size = nbytes - nread;
 315       file_ptr chunk_nread;
 316
 317       if (chunk_size > max_chunk_size)
 318         chunk_size = max_chunk_size;
 319
 320       chunk_nread = cache_bread_1 (abfd, buf + nread, chunk_size);
 321
 322       /* Update the nread count.
 323
 324          We just have to be careful of the case when cache_bread_1 returns
 325          a negative count:  If this is our first read, then set nread to
 326          that negative count in order to return that negative value to the
 327          caller.  Otherwise, don't add it to our total count, or we would
 328          end up returning a smaller number of bytes read than we actually
 329          did.  */
 330       if (nread == 0 || chunk_nread > 0)
 331         nread += chunk_nread;
 332
 333       if (chunk_nread < chunk_size)
 334         break;
 335     }
 336
 337   return nread;
 338 }
 339
 340 static file_ptr
 341 cache_bwrite (struct bfd *abfd, const void *where, file_ptr nbytes)
 342 {
 343   file_ptr nwrite;
 344   FILE *f = bfd_cache_lookup (abfd, 0);
 345   if (f == NULL)
 346     return 0;
 347   nwrite = fwrite (where, 1, nbytes, f);
 348   if (nwrite < nbytes && ferror (f))
 349     {
 350       bfd_set_error (bfd_error_system_call);
 351       return -1;
 352     }
 353   return nwrite;
 354 }
 355
 356 static int
 357 cache_bclose (struct bfd *abfd)
 358 {
 359   return bfd_cache_close (abfd);
 360 }
 361
 362 static int
 363 cache_bflush (struct bfd *abfd)
 364 {
 365   int sts;
 366   FILE *f = bfd_cache_lookup (abfd, CACHE_NO_OPEN);
 367   if (f == NULL)
 368     return 0;
 369   sts = fflush (f);
 370   if (sts < 0)
 371     bfd_set_error (bfd_error_system_call);
 372   return sts;
 373 }
 374
 375 static int
 376 cache_bstat (struct bfd *abfd, struct stat *sb)
 377 {
 378   int sts;
 379   FILE *f = bfd_cache_lookup (abfd, CACHE_NO_SEEK_ERROR);
 380   if (f == NULL)
 381     return -1;
 382   sts = fstat (fileno (f), sb);
 383   if (sts < 0)
 384     bfd_set_error (bfd_error_system_call);
 385   return sts;
 386 }
 387
 388 static const struct bfd_iovec cache_iovec = {
 389   &cache_bread, &cache_bwrite, &cache_btell, &cache_bseek,
 390   &cache_bclose, &cache_bflush, &cache_bstat
 391 };
 392
 393 /*
 394 INTERNAL_FUNCTION
 395         bfd_cache_init
 396
 397 SYNOPSIS
 398         bfd_boolean bfd_cache_init (bfd *abfd);
 399
 400 DESCRIPTION
 401         Add a newly opened BFD to the cache.
 402 */
 403
 404 bfd_boolean
 405 bfd_cache_init (bfd *abfd)
 406 {
 407   BFD_ASSERT (abfd->iostream != NULL);
 408   if (open_files >= BFD_CACHE_MAX_OPEN)
 409     {
 410       if (! close_one ())
 411         return FALSE;
 412     }
 413   abfd->iovec = &cache_iovec;
 414   insert (abfd);
 415   ++open_files;
 416   return TRUE;
 417 }
 418
 419 /*
 420 INTERNAL_FUNCTION
 421         bfd_cache_close
 422
 423 SYNOPSIS
 424         bfd_boolean bfd_cache_close (bfd *abfd);
 425
 426 DESCRIPTION
 427         Remove the BFD @var{abfd} from the cache. If the attached file is open,
 428         then close it too.
 429
 430 RETURNS
 431         <<FALSE>> is returned if closing the file fails, <<TRUE>> is
 432         returned if all is well.
 433 */
 434
 435 bfd_boolean
 436 bfd_cache_close (bfd *abfd)
 437 {
 438   if (abfd->iovec != &cache_iovec)
 439     return TRUE;
 440
 441   if (abfd->iostream == NULL)
 442     /* Previously closed.  */
 443     return TRUE;
 444
 445   return bfd_cache_delete (abfd);
 446 }
 447
 448 /*
 449 FUNCTION
 450         bfd_cache_close_all
 451
 452 SYNOPSIS
 453         bfd_boolean bfd_cache_close_all (void);
 454
 455 DESCRIPTION
 456         Remove all BFDs from the cache. If the attached file is open,
 457         then close it too.
 458
 459 RETURNS
 460         <<FALSE>> is returned if closing one of the file fails, <<TRUE>> is
 461         returned if all is well.
 462 */
 463
 464 bfd_boolean
 465 bfd_cache_close_all ()
 466 {
 467   bfd_boolean ret = TRUE;
 468
 469   while (bfd_last_cache != NULL)
 470     ret &= bfd_cache_close (bfd_last_cache);
 471
 472   return ret;
 473 }
 474
 475 /*
 476 INTERNAL_FUNCTION
 477         bfd_open_file
 478
 479 SYNOPSIS
 480         FILE* bfd_open_file (bfd *abfd);
 481
 482 DESCRIPTION
 483         Call the OS to open a file for @var{abfd}.  Return the <<FILE *>>
 484         (possibly <<NULL>>) that results from this operation.  Set up the
 485         BFD so that future accesses know the file is open. If the <<FILE *>>
 486         returned is <<NULL>>, then it won't have been put in the
 487         cache, so it won't have to be removed from it.
 488 */
 489
 490 FILE *
 491 bfd_open_file (bfd *abfd)
 492 {
 493   abfd->cacheable = TRUE;       /* Allow it to be closed later.  */
 494
 495   if (open_files >= BFD_CACHE_MAX_OPEN)
 496     {
 497       if (! close_one ())
 498         return NULL;
 499     }
 500
 501   switch (abfd->direction)
 502     {
 503     case read_direction:
 504     case no_direction:
 505       abfd->iostream = (PTR) real_fopen (abfd->filename, FOPEN_RB);
 506       break;
 507     case both_direction:
 508     case write_direction:
 509       if (abfd->opened_once)
 510         {
 511           abfd->iostream = (PTR) real_fopen (abfd->filename, FOPEN_RUB);
 512           if (abfd->iostream == NULL)
 513             abfd->iostream = (PTR) real_fopen (abfd->filename, FOPEN_WUB);
 514         }
 515       else
 516         {
 517           /* Create the file.
 518
 519              Some operating systems won't let us overwrite a running
 520              binary.  For them, we want to unlink the file first.
 521
 522              However, gcc 2.95 will create temporary files using
 523              O_EXCL and tight permissions to prevent other users from
 524              substituting other .o files during the compilation.  gcc
 525              will then tell the assembler to use the newly created
 526              file as an output file.  If we unlink the file here, we
 527              open a brief window when another user could still
 528              substitute a file.
 529
 530              So we unlink the output file if and only if it has
 531              non-zero size.  */
 532 #ifndef __MSDOS__
 533           /* Don't do this for MSDOS: it doesn't care about overwriting
 534              a running binary, but if this file is already open by
 535              another BFD, we will be in deep trouble if we delete an
 536              open file.  In fact, objdump does just that if invoked with
 537              the --info option.  */
 538           struct stat s;
 539
 540           if (stat (abfd->filename, &s) == 0 && s.st_size != 0)
 541             unlink_if_ordinary (abfd->filename);
 542 #endif
 543           abfd->iostream = (PTR) real_fopen (abfd->filename, FOPEN_WUB);
 544           abfd->opened_once = TRUE;
 545         }
 546       break;
 547     }
 548
 549   if (abfd->iostream == NULL)
 550     bfd_set_error (bfd_error_system_call);
 551   else
 552     {
 553       if (! bfd_cache_init (abfd))
 554         return NULL;
 555     }
 556
 557   return (FILE *) abfd->iostream;
 558 }