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