gdb/minsyms.c

   1 /* GDB routines for manipulating the minimal symbol tables.
   2    Copyright 1992 Free Software Foundation, Inc.
   3    Contributed by Cygnus Support, using pieces from other GDB modules.
   4
   5 This file is part of GDB.
   6
   7 This program is free software; you can redistribute it and/or modify
   8 it under the terms of the GNU General Public License as published by
   9 the Free Software Foundation; either version 2 of the License, or
  10 (at your option) any later version.
  11
  12 This program is distributed in the hope that it will be useful,
  13 but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15 GNU General Public License for more details.
  16
  17 You should have received a copy of the GNU General Public License
  18 along with this program; if not, write to the Free Software
  19 Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.  */
  20
  21
  22 /* This file contains support routines for creating, manipulating, and
  23    destroying minimal symbol tables.
  24
  25    Minimal symbol tables are used to hold some very basic information about
  26    all defined global symbols (text, data, bss, abs, etc).  The only two
  27    required pieces of information are the symbol's name and the address
  28    associated with that symbol.
  29
  30    In many cases, even if a file was compiled with no special options for
  31    debugging at all, as long as was not stripped it will contain sufficient
  32    information to build useful minimal symbol tables using this structure.
  33
  34    Even when a file contains enough debugging information to build a full
  35    symbol table, these minimal symbols are still useful for quickly mapping
  36    between names and addresses, and vice versa.  They are also sometimes used
  37    to figure out what full symbol table entries need to be read in. */
  38
  39
  40 #include <stdio.h>
  41 #include "defs.h"
  42 #include "symtab.h"
  43 #include "bfd.h"
  44 #include "symfile.h"
  45
  46 /* Accumulate the minimal symbols for each objfile in bunches of BUNCH_SIZE.
  47    At the end, copy them all into one newly allocated location on an objfile's
  48    symbol obstack.  */
  49
  50 #define BUNCH_SIZE 127
  51
  52 struct msym_bunch
  53 {
  54   struct msym_bunch *next;
  55   struct minimal_symbol contents[BUNCH_SIZE];
  56 };
  57
  58 /* Bunch currently being filled up.
  59    The next field points to chain of filled bunches.  */
  60
  61 static struct msym_bunch *msym_bunch;
  62
  63 /* Number of slots filled in current bunch.  */
  64
  65 static int msym_bunch_index;
  66
  67 /* Total number of minimal symbols recorded so far for the objfile.  */
  68
  69 static int msym_count;
  70
  71 /* Prototypes for local functions. */
  72
  73 static int
  74 compare_minimal_symbols PARAMS ((const void *, const void *));
  75
  76 static int
  77 compact_minimal_symbols PARAMS ((struct minimal_symbol *, int));
  78
  79 /* Call the function specified by FUNC for each currently available minimal
  80    symbol, for as long as this function continues to return NULL.  If the
  81    function ever returns non-NULL, then the iteration over the minimal
  82    symbols is terminated,, the result is returned to the caller.
  83
  84    The function called has full control over the form and content of the
  85    information returned via the non-NULL result, which may be as simple as a
  86    pointer to the minimal symbol that the iteration terminated on, or as
  87    complex as a pointer to a private structure containing multiple results. */
  88
  89 PTR
  90 iterate_over_msymbols (func, arg1, arg2, arg3)
  91      PTR (*func) PARAMS ((struct objfile *, struct minimal_symbol *,
  92                           PTR, PTR, PTR));
  93      PTR arg1;
  94      PTR arg2;
  95      PTR arg3;
  96 {
  97   register struct objfile *objfile;
  98   register struct minimal_symbol *msymbol;
  99   char *result = NULL;
 100
 101   for (objfile = object_files;
 102        objfile != NULL && result == NULL;
 103        objfile = objfile -> next)
 104     {
 105       for (msymbol = objfile -> msymbols;
 106            msymbol != NULL && msymbol -> name != NULL && result == NULL;
 107            msymbol++)
 108         {
 109           result = (*func)(objfile, msymbol, arg1, arg2, arg3);
 110         }
 111     }
 112   return (result);
 113 }
 114
 115 /* Look through all the current minimal symbol tables and find the first
 116    minimal symbol that matches NAME.  If OBJF is non-NULL, it specifies a
 117    particular objfile and the search is limited to that objfile.  Returns
 118    a pointer to the minimal symbol that matches, or NULL if no match is found.
 119
 120    Note:  One instance where their may be duplicate minimal symbols with
 121    the same name is when the symbol tables for a shared library and the
 122    symbol tables for an executable contain global symbols with the same
 123    names (the dynamic linker deals with the duplication). */
 124
 125 struct minimal_symbol *
 126 lookup_minimal_symbol (name, objf)
 127      register const char *name;
 128      struct objfile *objf;
 129 {
 130   struct objfile *objfile;
 131   struct minimal_symbol *msymbol;
 132   struct minimal_symbol *found_symbol = NULL;
 133
 134   for (objfile = object_files;
 135        objfile != NULL && found_symbol == NULL;
 136        objfile = objfile -> next)
 137     {
 138       if (objf == NULL || objf == objfile)
 139         {
 140           for (msymbol = objfile -> msymbols;
 141                msymbol != NULL && msymbol -> name != NULL &&
 142                found_symbol == NULL;
 143                msymbol++)
 144             {
 145               if (strcmp (msymbol -> name, name) == 0)
 146                 {
 147                   found_symbol = msymbol;
 148                 }
 149             }
 150         }
 151     }
 152   return (found_symbol);
 153 }
 154
 155
 156 /* Search through the minimal symbol table for each objfile and find the
 157    symbol whose address is the largest address that is still less than or
 158    equal to PC.  Returns a pointer to the minimal symbol if such a symbol
 159    is found, or NULL if PC is not in a suitable range.  Note that we need
 160    to look through ALL the minimal symbol tables before deciding on the
 161    symbol that comes closest to the specified PC. */
 162
 163 struct minimal_symbol *
 164 lookup_minimal_symbol_by_pc (pc)
 165      register CORE_ADDR pc;
 166 {
 167   register int lo;
 168   register int hi;
 169   register int new;
 170   register struct objfile *objfile;
 171   register struct minimal_symbol *msymbol;
 172   register struct minimal_symbol *best_symbol = NULL;
 173
 174   for (objfile = object_files;
 175        objfile != NULL;
 176        objfile = objfile -> next)
 177     {
 178       /* If this objfile has a minimal symbol table, go search it using
 179          a binary search.  Note that a minimal symbol table always consists
 180          of at least two symbols, a "real" symbol and the terminating
 181          "null symbol".  If there are no real symbols, then there is no
 182          minimal symbol table at all. */
 183
 184       if ((msymbol = objfile -> msymbols) != NULL)
 185         {
 186           lo = 0;
 187           hi = objfile -> minimal_symbol_count - 2;
 188
 189           /* This code assumes that the minimal symbols are sorted by
 190              ascending address values.  If the pc value is greater than or
 191              equal to the first symbol's address, then some symbol in this
 192              minimal symbol table is a suitable candidate for being the
 193              "best" symbol.  This includes the last real symbol, for cases
 194              where the pc value is larger than any address in this vector.
 195
 196              By iterating until the address associated with the current
 197              hi index (the endpoint of the test interval) is less than
 198              or equal to the desired pc value, we accomplish two things:
 199              (1) the case where the pc value is larger than any minimal
 200              symbol address is trivially solved, (2) the address associated
 201              with the hi index is always the one we want when the interation
 202              terminates.  In essence, we are iterating the test interval
 203              down until the pc value is pushed out of it from the high end.
 204
 205              Warning: this code is trickier than it would appear at first. */
 206
 207           if (pc >= msymbol[lo].address)
 208             {
 209               while (msymbol[hi].address > pc)
 210                 {
 211                   /* pc is still strictly less than highest address */
 212                   /* Note "new" will always be >= lo */
 213                   new = (lo + hi) / 2;
 214                   if ((msymbol[new].address >= pc) || (lo == new))
 215                     {
 216                       hi = new;
 217                     }
 218                   else
 219                     {
 220                       lo = new;
 221                     }
 222                 }
 223               /* The minimal symbol indexed by hi now is the best one in this
 224                  objfile's minimal symbol table.  See if it is the best one
 225                  overall. */
 226
 227               if ((best_symbol == NULL) ||
 228                   (best_symbol -> address < msymbol[hi].address))
 229                 {
 230                   best_symbol = &msymbol[hi];
 231                 }
 232             }
 233         }
 234     }
 235   return (best_symbol);
 236 }
 237
 238 /* Prepare to start collecting minimal symbols.  Note that presetting
 239    msym_bunch_index to BUNCH_SIZE causes the first call to save a minimal
 240    symbol to allocate the memory for the first bunch. */
 241
 242 void
 243 init_minimal_symbol_collection ()
 244 {
 245   msym_count = 0;
 246   msym_bunch = NULL;
 247   msym_bunch_index = BUNCH_SIZE;
 248 }
 249
 250 void
 251 prim_record_minimal_symbol (name, address, ms_type)
 252      const char *name;
 253      CORE_ADDR address;
 254      enum minimal_symbol_type ms_type;
 255 {
 256   register struct msym_bunch *new;
 257
 258   if (msym_bunch_index == BUNCH_SIZE)
 259     {
 260       new = (struct msym_bunch *) xmalloc (sizeof (struct msym_bunch));
 261       msym_bunch_index = 0;
 262       new -> next = msym_bunch;
 263       msym_bunch = new;
 264     }
 265   msym_bunch -> contents[msym_bunch_index].name = (char *) name;
 266   msym_bunch -> contents[msym_bunch_index].address = address;
 267   msym_bunch -> contents[msym_bunch_index].info = NULL;
 268   msym_bunch -> contents[msym_bunch_index].type = ms_type;
 269   msym_bunch_index++;
 270   msym_count++;
 271 }
 272
 273 /* Compare two minimal symbols by address and return a signed result based
 274    on unsigned comparisons, so that we sort into unsigned numeric order.  */
 275
 276 static int
 277 compare_minimal_symbols (fn1p, fn2p)
 278      const PTR fn1p;
 279      const PTR fn2p;
 280 {
 281   register const struct minimal_symbol *fn1;
 282   register const struct minimal_symbol *fn2;
 283
 284   fn1 = (const struct minimal_symbol *) fn1p;
 285   fn2 = (const struct minimal_symbol *) fn2p;
 286
 287   if (fn1 -> address < fn2 -> address)
 288     {
 289       return (-1);
 290     }
 291   else if (fn1 -> address > fn2 -> address)
 292     {
 293       return (1);
 294     }
 295   else
 296     {
 297       return (0);
 298     }
 299 }
 300
 301 /* Discard the currently collected minimal symbols, if any.  If we wish
 302    to save them for later use, we must have already copied them somewhere
 303    else before calling this function.
 304
 305    FIXME:  We could allocate the minimal symbol bunches on their own
 306    obstack and then simply blow the obstack away when we are done with
 307    it.  Is it worth the extra trouble though? */
 308
 309 /* ARGSUSED */
 310 void
 311 discard_minimal_symbols (foo)
 312      int foo;
 313 {
 314   register struct msym_bunch *next;
 315
 316   while (msym_bunch != NULL)
 317     {
 318       next = msym_bunch -> next;
 319       free (msym_bunch);
 320       msym_bunch = next;
 321     }
 322 }
 323
 324 /* Compact duplicate entries out of a minimal symbol table by walking
 325    through the table and compacting out entries with duplicate addresses
 326    and matching names.  Return the number of entries remaining.
 327
 328    On entry, the table resides between msymbol[0] and msymbol[mcount].
 329    On exit, it resides between msymbol[0] and msymbol[result_count].
 330
 331    When files contain multiple sources of symbol information, it is
 332    possible for the minimal symbol table to contain many duplicate entries.
 333    As an example, SVR4 systems use ELF formatted object files, which
 334    usually contain at least two different types of symbol tables (a
 335    standard ELF one and a smaller dynamic linking table), as well as
 336    DWARF debugging information for files compiled with -g.
 337
 338    Without compacting, the minimal symbol table for gdb itself contains
 339    over a 1000 duplicates, about a third of the total table size.  Aside
 340    from the potential trap of not noticing that two successive entries
 341    identify the same location, this duplication impacts the time required
 342    to linearly scan the table, which is done in a number of places.  So we
 343    just do one linear scan here and toss out the duplicates.
 344
 345    Note that we are not concerned here about recovering the space that
 346    is potentially freed up, because the strings themselves are allocated
 347    on the symbol_obstack, and will get automatically freed when the symbol
 348    table is freed.  The caller can free up the unused minimal symbols at
 349    the end of the compacted region if their allocation strategy allows it.
 350
 351    Also note we only go up to the next to last entry within the loop
 352    and then copy the last entry explicitly after the loop terminates.
 353
 354    Since the different sources of information for each symbol may
 355    have different levels of "completeness", we may have duplicates
 356    that have one entry with type "mst_unknown" and the other with a
 357    known type.  So if the one we are leaving alone has type mst_unknown,
 358    overwrite its type with the type from the one we are compacting out.  */
 359
 360 static int
 361 compact_minimal_symbols (msymbol, mcount)
 362      struct minimal_symbol *msymbol;
 363      int mcount;
 364 {
 365   struct minimal_symbol *copyfrom;
 366   struct minimal_symbol *copyto;
 367
 368   if (mcount > 0)
 369     {
 370       copyfrom = copyto = msymbol;
 371       while (copyfrom < msymbol + mcount - 1)
 372         {
 373           if (copyfrom -> address == (copyfrom + 1) -> address
 374               && (strcmp (copyfrom -> name, (copyfrom + 1) -> name) == 0))
 375             {
 376               if ((copyfrom + 1) -> type == mst_unknown)
 377                 {
 378                   (copyfrom + 1) -> type = copyfrom -> type;
 379                 }
 380               copyfrom++;
 381             }
 382           else
 383             {
 384               *copyto++ = *copyfrom++;
 385             }
 386         }
 387       *copyto++ = *copyfrom++;
 388       mcount = copyto - msymbol;
 389     }
 390   return (mcount);
 391 }
 392
 393 /* Add the minimal symbols in the existing bunches to the objfile's
 394    official minimal symbol table.  99% of the time, this adds the
 395    bunches to NO existing symbols.  Once in a while for shared
 396    libraries, we add symbols (e.g. common symbols) to an existing
 397    objfile.  */
 398
 399 void
 400 install_minimal_symbols (objfile)
 401      struct objfile *objfile;
 402 {
 403   register int bindex;
 404   register int mcount;
 405   register struct msym_bunch *bunch;
 406   register struct minimal_symbol *msymbols;
 407   int nbytes;
 408   int alloc_count;
 409
 410   if (msym_count > 0)
 411     {
 412       /* Allocate enough space in the obstack, into which we will gather the
 413          bunches of new and existing minimal symbols, sort them, and then
 414          compact out the duplicate entries.  Once we have a final table,
 415          we will give back the excess space.  */
 416
 417       alloc_count = msym_count + objfile->minimal_symbol_count + 1;
 418       obstack_blank (&objfile->symbol_obstack,
 419                      alloc_count * sizeof (struct minimal_symbol));
 420       msymbols = (struct minimal_symbol *)
 421                  obstack_base (&objfile->symbol_obstack);
 422
 423       /* Copy in the existing minimal symbols, if there are any.  */
 424
 425       if (objfile->minimal_symbol_count)
 426         memcpy ((char *)msymbols, (char *)objfile->msymbols,
 427                 objfile->minimal_symbol_count * sizeof (struct minimal_symbol));
 428
 429       /* Walk through the list of minimal symbol bunches, adding each symbol
 430          to the new contiguous array of symbols.  Note that we start with the
 431          current, possibly partially filled bunch (thus we use the current
 432          msym_bunch_index for the first bunch we copy over), and thereafter
 433          each bunch is full. */
 434
 435       mcount = objfile->minimal_symbol_count;
 436
 437       for (bunch = msym_bunch; bunch != NULL; bunch = bunch -> next)
 438         {
 439           for (bindex = 0; bindex < msym_bunch_index; bindex++, mcount++)
 440             {
 441               msymbols[mcount] = bunch -> contents[bindex];
 442 #ifdef NAMES_HAVE_UNDERSCORE
 443               if (msymbols[mcount].name[0] == '_')
 444                 {
 445                   msymbols[mcount].name++;
 446                 }
 447 #endif
 448 #ifdef SOME_NAMES_HAVE_DOT
 449               if (msymbols[mcount].name[0] == '.')
 450                 {
 451                   msymbols[mcount].name++;
 452                 }
 453 #endif
 454             }
 455           msym_bunch_index = BUNCH_SIZE;
 456         }
 457
 458       /* Sort the minimal symbols by address.  */
 459
 460       qsort (msymbols, mcount, sizeof (struct minimal_symbol),
 461              compare_minimal_symbols);
 462
 463       /* Compact out any duplicates, and free up whatever space we are
 464          no longer using.  */
 465
 466       mcount = compact_minimal_symbols (msymbols, mcount);
 467
 468       obstack_blank (&objfile->symbol_obstack,
 469         (mcount + 1 - alloc_count) * sizeof (struct minimal_symbol));
 470       msymbols = (struct minimal_symbol *)
 471         obstack_finish (&objfile->symbol_obstack);
 472
 473       /* We also terminate the minimal symbol table
 474          with a "null symbol", which is *not* included in the size of
 475          the table.  This makes it easier to find the end of the table
 476          when we are handed a pointer to some symbol in the middle of it.
 477          Zero out the fields in the "null symbol" allocated at the end
 478          of the array.  Note that the symbol count does *not* include
 479          this null symbol, which is why it is indexed by mcount and not
 480          mcount-1. */
 481
 482       msymbols[mcount].name = NULL;
 483       msymbols[mcount].address = 0;
 484       msymbols[mcount].info = NULL;
 485       msymbols[mcount].type = mst_unknown;
 486
 487       /* Attach the minimal symbol table to the specified objfile.
 488          The strings themselves are also located in the symbol_obstack
 489          of this objfile.  */
 490
 491       objfile -> minimal_symbol_count = mcount;
 492       objfile -> msymbols = msymbols;
 493     }
 494 }
 495