gdb/gnu-v3-abi.c

   1 /* Abstraction of GNU v3 abi.
   2    Contributed by Jim Blandy <jimb@redhat.com>
   3
   4    Copyright 2001, 2002, 2003 Free Software Foundation, Inc.
   5
   6    This file is part of GDB.
   7
   8    This program is free software; you can redistribute it and/or
   9    modify it under the terms of the GNU General Public License as
  10    published by the Free Software Foundation; either version 2 of the
  11    License, or (at your option) any later version.
  12
  13    This program is distributed in the hope that it will be useful,
  14    but WITHOUT ANY WARRANTY; without even the implied warranty of
  15    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16    GNU General Public License for more details.
  17
  18    You should have received a copy of the GNU General Public License
  19    along with this program; if not, write to the Free Software
  20    Foundation, Inc., 59 Temple Place - Suite 330,
  21    Boston, MA 02111-1307, USA.  */
  22
  23 #include "defs.h"
  24 #include "value.h"
  25 #include "cp-abi.h"
  26 #include "cp-support.h"
  27 #include "demangle.h"
  28 #include "gdb_assert.h"
  29 #include "gdb_string.h"
  30
  31 static struct cp_abi_ops gnu_v3_abi_ops;
  32
  33 static int
  34 gnuv3_is_vtable_name (const char *name)
  35 {
  36   return strncmp (name, "_ZTV", 4) == 0;
  37 }
  38
  39 static int
  40 gnuv3_is_operator_name (const char *name)
  41 {
  42   return strncmp (name, "operator", 8) == 0;
  43 }
  44
  45
  46 /* To help us find the components of a vtable, we build ourselves a
  47    GDB type object representing the vtable structure.  Following the
  48    V3 ABI, it goes something like this:
  49
  50    struct gdb_gnu_v3_abi_vtable {
  51
  52      / * An array of virtual call and virtual base offsets.  The real
  53          length of this array depends on the class hierarchy; we use
  54          negative subscripts to access the elements.  Yucky, but
  55          better than the alternatives.  * /
  56      ptrdiff_t vcall_and_vbase_offsets[0];
  57
  58      / * The offset from a virtual pointer referring to this table
  59          to the top of the complete object.  * /
  60      ptrdiff_t offset_to_top;
  61
  62      / * The type_info pointer for this class.  This is really a
  63          std::type_info *, but GDB doesn't really look at the
  64          type_info object itself, so we don't bother to get the type
  65          exactly right.  * /
  66      void *type_info;
  67
  68      / * Virtual table pointers in objects point here.  * /
  69
  70      / * Virtual function pointers.  Like the vcall/vbase array, the
  71          real length of this table depends on the class hierarchy.  * /
  72      void (*virtual_functions[0]) ();
  73
  74    };
  75
  76    The catch, of course, is that the exact layout of this table
  77    depends on the ABI --- word size, endianness, alignment, etc.  So
  78    the GDB type object is actually a per-architecture kind of thing.
  79
  80    vtable_type_gdbarch_data is a gdbarch per-architecture data pointer
  81    which refers to the struct type * for this structure, laid out
  82    appropriately for the architecture.  */
  83 static struct gdbarch_data *vtable_type_gdbarch_data;
  84
  85
  86 /* Human-readable names for the numbers of the fields above.  */
  87 enum {
  88   vtable_field_vcall_and_vbase_offsets,
  89   vtable_field_offset_to_top,
  90   vtable_field_type_info,
  91   vtable_field_virtual_functions
  92 };
  93
  94
  95 /* Return a GDB type representing `struct gdb_gnu_v3_abi_vtable',
  96    described above, laid out appropriately for ARCH.
  97
  98    We use this function as the gdbarch per-architecture data
  99    initialization function.  We assume that the gdbarch framework
 100    calls the per-architecture data initialization functions after it
 101    sets current_gdbarch to the new architecture.  */
 102 static void *
 103 build_gdb_vtable_type (struct gdbarch *arch)
 104 {
 105   struct type *t;
 106   struct field *field_list, *field;
 107   int offset;
 108
 109   struct type *void_ptr_type
 110     = lookup_pointer_type (builtin_type_void);
 111   struct type *ptr_to_void_fn_type
 112     = lookup_pointer_type (lookup_function_type (builtin_type_void));
 113
 114   /* ARCH can't give us the true ptrdiff_t type, so we guess.  */
 115   struct type *ptrdiff_type
 116     = init_type (TYPE_CODE_INT, TARGET_PTR_BIT / TARGET_CHAR_BIT, 0,
 117                  "ptrdiff_t", 0);
 118
 119   /* We assume no padding is necessary, since GDB doesn't know
 120      anything about alignment at the moment.  If this assumption bites
 121      us, we should add a gdbarch method which, given a type, returns
 122      the alignment that type requires, and then use that here.  */
 123
 124   /* Build the field list.  */
 125   field_list = xmalloc (sizeof (struct field [4]));
 126   memset (field_list, 0, sizeof (struct field [4]));
 127   field = &field_list[0];
 128   offset = 0;
 129
 130   /* ptrdiff_t vcall_and_vbase_offsets[0]; */
 131   FIELD_NAME (*field) = "vcall_and_vbase_offsets";
 132   FIELD_TYPE (*field)
 133     = create_array_type (0, ptrdiff_type,
 134                          create_range_type (0, builtin_type_int, 0, -1));
 135   FIELD_BITPOS (*field) = offset * TARGET_CHAR_BIT;
 136   offset += TYPE_LENGTH (FIELD_TYPE (*field));
 137   field++;
 138
 139   /* ptrdiff_t offset_to_top; */
 140   FIELD_NAME (*field) = "offset_to_top";
 141   FIELD_TYPE (*field) = ptrdiff_type;
 142   FIELD_BITPOS (*field) = offset * TARGET_CHAR_BIT;
 143   offset += TYPE_LENGTH (FIELD_TYPE (*field));
 144   field++;
 145
 146   /* void *type_info; */
 147   FIELD_NAME (*field) = "type_info";
 148   FIELD_TYPE (*field) = void_ptr_type;
 149   FIELD_BITPOS (*field) = offset * TARGET_CHAR_BIT;
 150   offset += TYPE_LENGTH (FIELD_TYPE (*field));
 151   field++;
 152
 153   /* void (*virtual_functions[0]) (); */
 154   FIELD_NAME (*field) = "virtual_functions";
 155   FIELD_TYPE (*field)
 156     = create_array_type (0, ptr_to_void_fn_type,
 157                          create_range_type (0, builtin_type_int, 0, -1));
 158   FIELD_BITPOS (*field) = offset * TARGET_CHAR_BIT;
 159   offset += TYPE_LENGTH (FIELD_TYPE (*field));
 160   field++;
 161
 162   /* We assumed in the allocation above that there were four fields.  */
 163   gdb_assert (field == (field_list + 4));
 164
 165   t = init_type (TYPE_CODE_STRUCT, offset, 0, 0, 0);
 166   TYPE_NFIELDS (t) = field - field_list;
 167   TYPE_FIELDS (t) = field_list;
 168   TYPE_TAG_NAME (t) = "gdb_gnu_v3_abi_vtable";
 169
 170   return t;
 171 }
 172
 173
 174 /* Return the offset from the start of the imaginary `struct
 175    gdb_gnu_v3_abi_vtable' object to the vtable's "address point"
 176    (i.e., where objects' virtual table pointers point).  */
 177 static int
 178 vtable_address_point_offset (void)
 179 {
 180   struct type *vtable_type = gdbarch_data (current_gdbarch,
 181                                            vtable_type_gdbarch_data);
 182
 183   return (TYPE_FIELD_BITPOS (vtable_type, vtable_field_virtual_functions)
 184           / TARGET_CHAR_BIT);
 185 }
 186
 187
 188 static struct type *
 189 gnuv3_rtti_type (struct value *value,
 190                  int *full_p, int *top_p, int *using_enc_p)
 191 {
 192   struct type *vtable_type = gdbarch_data (current_gdbarch,
 193                                            vtable_type_gdbarch_data);
 194   struct type *value_type = check_typedef (VALUE_TYPE (value));
 195   CORE_ADDR vtable_address;
 196   struct value *vtable;
 197   struct minimal_symbol *vtable_symbol;
 198   const char *vtable_symbol_name;
 199   const char *class_name;
 200   struct type *run_time_type;
 201   struct type *base_type;
 202   LONGEST offset_to_top;
 203
 204   /* We only have RTTI for class objects.  */
 205   if (TYPE_CODE (value_type) != TYPE_CODE_CLASS)
 206     return NULL;
 207
 208   /* If we can't find the virtual table pointer for value_type, we
 209      can't find the RTTI.  */
 210   fill_in_vptr_fieldno (value_type);
 211   if (TYPE_VPTR_FIELDNO (value_type) == -1)
 212     return NULL;
 213
 214   if (using_enc_p)
 215     *using_enc_p = 0;
 216
 217   /* Fetch VALUE's virtual table pointer, and tweak it to point at
 218      an instance of our imaginary gdb_gnu_v3_abi_vtable structure.  */
 219   base_type = check_typedef (TYPE_VPTR_BASETYPE (value_type));
 220   if (value_type != base_type)
 221     {
 222       value = value_cast (base_type, value);
 223       if (using_enc_p)
 224         *using_enc_p = 1;
 225     }
 226   vtable_address
 227     = value_as_address (value_field (value, TYPE_VPTR_FIELDNO (value_type)));
 228   vtable = value_at_lazy (vtable_type,
 229                           vtable_address - vtable_address_point_offset ());
 230
 231   /* Find the linker symbol for this vtable.  */
 232   vtable_symbol
 233     = lookup_minimal_symbol_by_pc (VALUE_ADDRESS (vtable)
 234                                    + VALUE_OFFSET (vtable)
 235                                    + VALUE_EMBEDDED_OFFSET (vtable));
 236   if (! vtable_symbol)
 237     return NULL;
 238
 239   /* The symbol's demangled name should be something like "vtable for
 240      CLASS", where CLASS is the name of the run-time type of VALUE.
 241      If we didn't like this approach, we could instead look in the
 242      type_info object itself to get the class name.  But this way
 243      should work just as well, and doesn't read target memory.  */
 244   vtable_symbol_name = SYMBOL_DEMANGLED_NAME (vtable_symbol);
 245   if (vtable_symbol_name == NULL
 246       || strncmp (vtable_symbol_name, "vtable for ", 11))
 247     {
 248       warning ("can't find linker symbol for virtual table for `%s' value",
 249                TYPE_NAME (value_type));
 250       if (vtable_symbol_name)
 251         warning ("  found `%s' instead", vtable_symbol_name);
 252       return NULL;
 253     }
 254   class_name = vtable_symbol_name + 11;
 255
 256   /* Try to look up the class name as a type name.  */
 257   /* FIXME: chastain/2003-11-26: block=NULL is bogus.  See pr gdb/1465. */
 258   run_time_type = cp_lookup_rtti_type (class_name, NULL);
 259   if (run_time_type == NULL)
 260     return NULL;
 261
 262   /* Get the offset from VALUE to the top of the complete object.
 263      NOTE: this is the reverse of the meaning of *TOP_P.  */
 264   offset_to_top
 265     = value_as_long (value_field (vtable, vtable_field_offset_to_top));
 266
 267   if (full_p)
 268     *full_p = (- offset_to_top == VALUE_EMBEDDED_OFFSET (value)
 269                && (TYPE_LENGTH (VALUE_ENCLOSING_TYPE (value))
 270                    >= TYPE_LENGTH (run_time_type)));
 271   if (top_p)
 272     *top_p = - offset_to_top;
 273
 274   return run_time_type;
 275 }
 276
 277
 278 static struct value *
 279 gnuv3_virtual_fn_field (struct value **value_p,
 280                         struct fn_field *f, int j,
 281                         struct type *type, int offset)
 282 {
 283   struct type *vtable_type = gdbarch_data (current_gdbarch,
 284                                            vtable_type_gdbarch_data);
 285   struct value *value = *value_p;
 286   struct type *value_type = check_typedef (VALUE_TYPE (value));
 287   struct type *vfn_base;
 288   CORE_ADDR vtable_address;
 289   struct value *vtable;
 290   struct value *vfn;
 291
 292   /* Some simple sanity checks.  */
 293   if (TYPE_CODE (value_type) != TYPE_CODE_CLASS)
 294     error ("Only classes can have virtual functions.");
 295
 296   /* Find the base class that defines this virtual function.  */
 297   vfn_base = TYPE_FN_FIELD_FCONTEXT (f, j);
 298   if (! vfn_base)
 299     /* In programs compiled with G++ version 1, the debug info doesn't
 300        say which base class defined the virtual function.  We'll guess
 301        it's the same base class that has our vtable; this is wrong for
 302        multiple inheritance, but it's better than nothing.  */
 303     vfn_base = TYPE_VPTR_BASETYPE (type);
 304
 305   /* This type may have been defined before its virtual function table
 306      was.  If so, fill in the virtual function table entry for the
 307      type now.  */
 308   if (TYPE_VPTR_FIELDNO (vfn_base) < 0)
 309     fill_in_vptr_fieldno (vfn_base);
 310   if (TYPE_VPTR_FIELDNO (vfn_base) < 0)
 311     error ("Could not find virtual table pointer for class \"%s\".",
 312            TYPE_TAG_NAME (vfn_base) ? TYPE_TAG_NAME (vfn_base) : "<unknown>");
 313
 314   /* Now that we know which base class is defining our virtual
 315      function, cast our value to that baseclass.  This takes care of
 316      any necessary `this' adjustments.  */
 317   if (vfn_base != value_type)
 318     value = value_cast (vfn_base, value);
 319
 320   /* Now value is an object of the appropriate base type.  Fetch its
 321      virtual table.  */
 322   /* It might be possible to do this cast at the same time as the above.
 323      Does multiple inheritance affect this?
 324      Can this even trigger, or is TYPE_VPTR_BASETYPE idempotent?
 325   */
 326   if (TYPE_VPTR_BASETYPE (vfn_base) != vfn_base)
 327     value = value_cast (TYPE_VPTR_BASETYPE (vfn_base), value);
 328   vtable_address
 329     = value_as_address (value_field (value, TYPE_VPTR_FIELDNO (vfn_base)));
 330
 331   vtable = value_at_lazy (vtable_type,
 332                           vtable_address - vtable_address_point_offset ());
 333
 334   /* Fetch the appropriate function pointer from the vtable.  */
 335   vfn = value_subscript (value_field (vtable, vtable_field_virtual_functions),
 336                          value_from_longest (builtin_type_int,
 337                                              TYPE_FN_FIELD_VOFFSET (f, j)));
 338
 339   /* Cast the function pointer to the appropriate type.  */
 340   vfn = value_cast (lookup_pointer_type (TYPE_FN_FIELD_TYPE (f, j)),
 341                     vfn);
 342
 343   /* Is (type)value always numerically the same as (vfn_base)value?
 344      If so we can spare this cast and use one of the ones above.  */
 345   *value_p = value_addr (value_cast (type, *value_p));
 346
 347   return vfn;
 348 }
 349
 350 /* Compute the offset of the baseclass which is
 351    the INDEXth baseclass of class TYPE,
 352    for value at VALADDR (in host) at ADDRESS (in target).
 353    The result is the offset of the baseclass value relative
 354    to (the address of)(ARG) + OFFSET.
 355
 356    -1 is returned on error. */
 357 static int
 358 gnuv3_baseclass_offset (struct type *type, int index, char *valaddr,
 359                         CORE_ADDR address)
 360 {
 361   struct type *vtable_type = gdbarch_data (current_gdbarch,
 362                                            vtable_type_gdbarch_data);
 363   struct value *vtable;
 364   struct type *vbasetype;
 365   struct value *offset_val, *vbase_array;
 366   CORE_ADDR vtable_address;
 367   long int cur_base_offset, base_offset;
 368
 369   /* If it isn't a virtual base, this is easy.  The offset is in the
 370      type definition.  */
 371   if (!BASETYPE_VIA_VIRTUAL (type, index))
 372     return TYPE_BASECLASS_BITPOS (type, index) / 8;
 373
 374   /* To access a virtual base, we need to use the vbase offset stored in
 375      our vtable.  Recent GCC versions provide this information.  If it isn't
 376      available, we could get what we needed from RTTI, or from drawing the
 377      complete inheritance graph based on the debug info.  Neither is
 378      worthwhile.  */
 379   cur_base_offset = TYPE_BASECLASS_BITPOS (type, index) / 8;
 380   if (cur_base_offset >= - vtable_address_point_offset ())
 381     error ("Expected a negative vbase offset (old compiler?)");
 382
 383   cur_base_offset = cur_base_offset + vtable_address_point_offset ();
 384   if ((- cur_base_offset) % TYPE_LENGTH (builtin_type_void_data_ptr) != 0)
 385     error ("Misaligned vbase offset.");
 386   cur_base_offset = cur_base_offset
 387     / ((int) TYPE_LENGTH (builtin_type_void_data_ptr));
 388
 389   /* We're now looking for the cur_base_offset'th entry (negative index)
 390      in the vcall_and_vbase_offsets array.  We used to cast the object to
 391      its TYPE_VPTR_BASETYPE, and reference the vtable as TYPE_VPTR_FIELDNO;
 392      however, that cast can not be done without calling baseclass_offset again
 393      if the TYPE_VPTR_BASETYPE is a virtual base class, as described in the
 394      v3 C++ ABI Section 2.4.I.2.b.  Fortunately the ABI guarantees that the
 395      vtable pointer will be located at the beginning of the object, so we can
 396      bypass the casting.  Verify that the TYPE_VPTR_FIELDNO is in fact at the
 397      start of whichever baseclass it resides in, as a sanity measure - iff
 398      we have debugging information for that baseclass.  */
 399
 400   vbasetype = TYPE_VPTR_BASETYPE (type);
 401   if (TYPE_VPTR_FIELDNO (vbasetype) < 0)
 402     fill_in_vptr_fieldno (vbasetype);
 403
 404   if (TYPE_VPTR_FIELDNO (vbasetype) >= 0
 405       && TYPE_FIELD_BITPOS (vbasetype, TYPE_VPTR_FIELDNO (vbasetype)) != 0)
 406     error ("Illegal vptr offset in class %s",
 407            TYPE_NAME (vbasetype) ? TYPE_NAME (vbasetype) : "<unknown>");
 408
 409   vtable_address = value_as_address (value_at_lazy (builtin_type_void_data_ptr,
 410                                                     address));
 411   vtable = value_at_lazy (vtable_type,
 412                           vtable_address - vtable_address_point_offset ());
 413   offset_val = value_from_longest(builtin_type_int, cur_base_offset);
 414   vbase_array = value_field (vtable, vtable_field_vcall_and_vbase_offsets);
 415   base_offset = value_as_long (value_subscript (vbase_array, offset_val));
 416   return base_offset;
 417 }
 418
 419 static void
 420 init_gnuv3_ops (void)
 421 {
 422   vtable_type_gdbarch_data = gdbarch_data_register_post_init (build_gdb_vtable_type);
 423
 424   gnu_v3_abi_ops.shortname = "gnu-v3";
 425   gnu_v3_abi_ops.longname = "GNU G++ Version 3 ABI";
 426   gnu_v3_abi_ops.doc = "G++ Version 3 ABI";
 427   gnu_v3_abi_ops.is_destructor_name = is_gnu_v3_mangled_dtor;
 428   gnu_v3_abi_ops.is_constructor_name = is_gnu_v3_mangled_ctor;
 429   gnu_v3_abi_ops.is_vtable_name = gnuv3_is_vtable_name;
 430   gnu_v3_abi_ops.is_operator_name = gnuv3_is_operator_name;
 431   gnu_v3_abi_ops.rtti_type = gnuv3_rtti_type;
 432   gnu_v3_abi_ops.virtual_fn_field = gnuv3_virtual_fn_field;
 433   gnu_v3_abi_ops.baseclass_offset = gnuv3_baseclass_offset;
 434 }
 435
 436 extern initialize_file_ftype _initialize_gnu_v3_abi; /* -Wmissing-prototypes */
 437
 438 void
 439 _initialize_gnu_v3_abi (void)
 440 {
 441   init_gnuv3_ops ();
 442
 443   register_cp_abi (&gnu_v3_abi_ops);
 444 }