gdb/gnu-v3-abi.c

   1 /* Abstraction of GNU v3 abi.
   2    Contributed by Jim Blandy <jimb@redhat.com>
   3
   4    Copyright 2001, 2002 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 "demangle.h"
  27 #include "gdb_assert.h"
  28 #include "gdb_string.h"
  29
  30 static struct cp_abi_ops gnu_v3_abi_ops;
  31
  32 static int
  33 gnuv3_is_vtable_name (const char *name)
  34 {
  35   return strncmp (name, "_ZTV", 4) == 0;
  36 }
  37
  38 static int
  39 gnuv3_is_operator_name (const char *name)
  40 {
  41   return strncmp (name, "operator", 8) == 0;
  42 }
  43
  44
  45 /* To help us find the components of a vtable, we build ourselves a
  46    GDB type object representing the vtable structure.  Following the
  47    V3 ABI, it goes something like this:
  48
  49    struct gdb_gnu_v3_abi_vtable {
  50
  51      / * An array of virtual call and virtual base offsets.  The real
  52          length of this array depends on the class hierarchy; we use
  53          negative subscripts to access the elements.  Yucky, but
  54          better than the alternatives.  * /
  55      ptrdiff_t vcall_and_vbase_offsets[0];
  56
  57      / * The offset from a virtual pointer referring to this table
  58          to the top of the complete object.  * /
  59      ptrdiff_t offset_to_top;
  60
  61      / * The type_info pointer for this class.  This is really a
  62          std::type_info *, but GDB doesn't really look at the
  63          type_info object itself, so we don't bother to get the type
  64          exactly right.  * /
  65      void *type_info;
  66
  67      / * Virtual table pointers in objects point here.  * /
  68
  69      / * Virtual function pointers.  Like the vcall/vbase array, the
  70          real length of this table depends on the class hierarchy.  * /
  71      void (*virtual_functions[0]) ();
  72
  73    };
  74
  75    The catch, of course, is that the exact layout of this table
  76    depends on the ABI --- word size, endianness, alignment, etc.  So
  77    the GDB type object is actually a per-architecture kind of thing.
  78
  79    vtable_type_gdbarch_data is a gdbarch per-architecture data pointer
  80    which refers to the struct type * for this structure, laid out
  81    appropriately for the architecture.  */
  82 static struct gdbarch_data *vtable_type_gdbarch_data;
  83
  84
  85 /* Human-readable names for the numbers of the fields above.  */
  86 enum {
  87   vtable_field_vcall_and_vbase_offsets,
  88   vtable_field_offset_to_top,
  89   vtable_field_type_info,
  90   vtable_field_virtual_functions
  91 };
  92
  93
  94 /* Return a GDB type representing `struct gdb_gnu_v3_abi_vtable',
  95    described above, laid out appropriately for ARCH.
  96
  97    We use this function as the gdbarch per-architecture data
  98    initialization function.  We assume that the gdbarch framework
  99    calls the per-architecture data initialization functions after it
 100    sets current_gdbarch to the new architecture.  */
 101 static void *
 102 build_gdb_vtable_type (struct gdbarch *arch)
 103 {
 104   struct type *t;
 105   struct field *field_list, *field;
 106   int offset;
 107
 108   struct type *void_ptr_type
 109     = lookup_pointer_type (builtin_type_void);
 110   struct type *ptr_to_void_fn_type
 111     = lookup_pointer_type (lookup_function_type (builtin_type_void));
 112
 113   /* ARCH can't give us the true ptrdiff_t type, so we guess.  */
 114   struct type *ptrdiff_type
 115     = init_type (TYPE_CODE_INT, TARGET_PTR_BIT / TARGET_CHAR_BIT, 0,
 116                  "ptrdiff_t", 0);
 117
 118   /* We assume no padding is necessary, since GDB doesn't know
 119      anything about alignment at the moment.  If this assumption bites
 120      us, we should add a gdbarch method which, given a type, returns
 121      the alignment that type requires, and then use that here.  */
 122
 123   /* Build the field list.  */
 124   field_list = xmalloc (sizeof (struct field [4]));
 125   memset (field_list, 0, sizeof (struct field [4]));
 126   field = &field_list[0];
 127   offset = 0;
 128
 129   /* ptrdiff_t vcall_and_vbase_offsets[0]; */
 130   FIELD_NAME (*field) = "vcall_and_vbase_offsets";
 131   FIELD_TYPE (*field)
 132     = create_array_type (0, ptrdiff_type,
 133                          create_range_type (0, builtin_type_int, 0, -1));
 134   FIELD_BITPOS (*field) = offset * TARGET_CHAR_BIT;
 135   offset += TYPE_LENGTH (FIELD_TYPE (*field));
 136   field++;
 137
 138   /* ptrdiff_t offset_to_top; */
 139   FIELD_NAME (*field) = "offset_to_top";
 140   FIELD_TYPE (*field) = ptrdiff_type;
 141   FIELD_BITPOS (*field) = offset * TARGET_CHAR_BIT;
 142   offset += TYPE_LENGTH (FIELD_TYPE (*field));
 143   field++;
 144
 145   /* void *type_info; */
 146   FIELD_NAME (*field) = "type_info";
 147   FIELD_TYPE (*field) = void_ptr_type;
 148   FIELD_BITPOS (*field) = offset * TARGET_CHAR_BIT;
 149   offset += TYPE_LENGTH (FIELD_TYPE (*field));
 150   field++;
 151
 152   /* void (*virtual_functions[0]) (); */
 153   FIELD_NAME (*field) = "virtual_functions";
 154   FIELD_TYPE (*field)
 155     = create_array_type (0, ptr_to_void_fn_type,
 156                          create_range_type (0, builtin_type_int, 0, -1));
 157   FIELD_BITPOS (*field) = offset * TARGET_CHAR_BIT;
 158   offset += TYPE_LENGTH (FIELD_TYPE (*field));
 159   field++;
 160
 161   /* We assumed in the allocation above that there were four fields.  */
 162   gdb_assert (field == (field_list + 4));
 163
 164   t = init_type (TYPE_CODE_STRUCT, offset, 0, 0, 0);
 165   TYPE_NFIELDS (t) = field - field_list;
 166   TYPE_FIELDS (t) = field_list;
 167   TYPE_TAG_NAME (t) = "gdb_gnu_v3_abi_vtable";
 168
 169   return t;
 170 }
 171
 172
 173 /* Return the offset from the start of the imaginary `struct
 174    gdb_gnu_v3_abi_vtable' object to the vtable's "address point"
 175    (i.e., where objects' virtual table pointers point).  */
 176 static int
 177 vtable_address_point_offset (void)
 178 {
 179   struct type *vtable_type = gdbarch_data (current_gdbarch,
 180                                            vtable_type_gdbarch_data);
 181
 182   return (TYPE_FIELD_BITPOS (vtable_type, vtable_field_virtual_functions)
 183           / TARGET_CHAR_BIT);
 184 }
 185
 186
 187 static struct type *
 188 gnuv3_rtti_type (struct value *value,
 189                  int *full_p, int *top_p, int *using_enc_p)
 190 {
 191   struct type *vtable_type = gdbarch_data (current_gdbarch,
 192                                            vtable_type_gdbarch_data);
 193   struct type *value_type = check_typedef (VALUE_TYPE (value));
 194   CORE_ADDR vtable_address;
 195   struct value *vtable;
 196   struct minimal_symbol *vtable_symbol;
 197   const char *vtable_symbol_name;
 198   const char *class_name;
 199   struct symbol *class_symbol;
 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                           VALUE_BFD_SECTION (value));
 231
 232   /* Find the linker symbol for this vtable.  */
 233   vtable_symbol
 234     = lookup_minimal_symbol_by_pc (VALUE_ADDRESS (vtable)
 235                                    + VALUE_OFFSET (vtable)
 236                                    + VALUE_EMBEDDED_OFFSET (vtable));
 237   if (! vtable_symbol)
 238     return NULL;
 239
 240   /* The symbol's demangled name should be something like "vtable for
 241      CLASS", where CLASS is the name of the run-time type of VALUE.
 242      If we didn't like this approach, we could instead look in the
 243      type_info object itself to get the class name.  But this way
 244      should work just as well, and doesn't read target memory.  */
 245   vtable_symbol_name = SYMBOL_DEMANGLED_NAME (vtable_symbol);
 246   if (vtable_symbol_name == NULL
 247       || strncmp (vtable_symbol_name, "vtable for ", 11))
 248     {
 249       warning ("can't find linker symbol for virtual table for `%s' value",
 250                TYPE_NAME (value_type));
 251       if (vtable_symbol_name)
 252         warning ("  found `%s' instead", vtable_symbol_name);
 253       return NULL;
 254     }
 255   class_name = vtable_symbol_name + 11;
 256
 257   /* Try to look up the class name as a type name.  */
 258   class_symbol = lookup_symbol (class_name, 0, STRUCT_NAMESPACE, 0, 0);
 259   if (! class_symbol)
 260     {
 261       warning ("can't find class named `%s', as given by C++ RTTI", class_name);
 262       return NULL;
 263     }
 264
 265   /* Make sure the type symbol is sane.  (An earlier version of this
 266      code would find constructor functions, who have the same name as
 267      the class.)  */
 268   if (SYMBOL_CLASS (class_symbol) != LOC_TYPEDEF
 269       || TYPE_CODE (SYMBOL_TYPE (class_symbol)) != TYPE_CODE_CLASS)
 270     {
 271       warning ("C++ RTTI gives a class name of `%s', but that isn't a type name",
 272                class_name);
 273       return NULL;
 274     }
 275
 276   /* This is the object's run-time type!  */
 277   run_time_type = SYMBOL_TYPE (class_symbol);
 278
 279   /* Get the offset from VALUE to the top of the complete object.
 280      NOTE: this is the reverse of the meaning of *TOP_P.  */
 281   offset_to_top
 282     = value_as_long (value_field (vtable, vtable_field_offset_to_top));
 283
 284   if (full_p)
 285     *full_p = (- offset_to_top == VALUE_EMBEDDED_OFFSET (value)
 286                && (TYPE_LENGTH (VALUE_ENCLOSING_TYPE (value))
 287                    >= TYPE_LENGTH (run_time_type)));
 288   if (top_p)
 289     *top_p = - offset_to_top;
 290
 291   return run_time_type;
 292 }
 293
 294
 295 static struct value *
 296 gnuv3_virtual_fn_field (struct value **value_p,
 297                         struct fn_field *f, int j,
 298                         struct type *type, int offset)
 299 {
 300   struct type *vtable_type = gdbarch_data (current_gdbarch,
 301                                            vtable_type_gdbarch_data);
 302   struct value *value = *value_p;
 303   struct type *value_type = check_typedef (VALUE_TYPE (value));
 304   struct type *vfn_base;
 305   CORE_ADDR vtable_address;
 306   struct value *vtable;
 307   struct value *vfn;
 308
 309   /* Some simple sanity checks.  */
 310   if (TYPE_CODE (value_type) != TYPE_CODE_CLASS)
 311     error ("Only classes can have virtual functions.");
 312
 313   /* Find the base class that defines this virtual function.  */
 314   vfn_base = TYPE_FN_FIELD_FCONTEXT (f, j);
 315   if (! vfn_base)
 316     /* In programs compiled with G++ version 1, the debug info doesn't
 317        say which base class defined the virtual function.  We'll guess
 318        it's the same base class that has our vtable; this is wrong for
 319        multiple inheritance, but it's better than nothing.  */
 320     vfn_base = TYPE_VPTR_BASETYPE (type);
 321
 322   /* This type may have been defined before its virtual function table
 323      was.  If so, fill in the virtual function table entry for the
 324      type now.  */
 325   if (TYPE_VPTR_FIELDNO (vfn_base) < 0)
 326     fill_in_vptr_fieldno (vfn_base);
 327   if (TYPE_VPTR_FIELDNO (vfn_base) < 0)
 328     error ("Could not find virtual table pointer for class \"%s\".",
 329            TYPE_TAG_NAME (vfn_base) ? TYPE_TAG_NAME (vfn_base) : "<unknown>");
 330
 331   /* Now that we know which base class is defining our virtual
 332      function, cast our value to that baseclass.  This takes care of
 333      any necessary `this' adjustments.  */
 334   if (vfn_base != value_type)
 335     value = value_cast (vfn_base, value);
 336
 337   /* Now value is an object of the appropriate base type.  Fetch its
 338      virtual table.  */
 339   /* It might be possible to do this cast at the same time as the above.
 340      Does multiple inheritance affect this?
 341      Can this even trigger, or is TYPE_VPTR_BASETYPE idempotent?
 342   */
 343   if (TYPE_VPTR_BASETYPE (vfn_base) != vfn_base)
 344     value = value_cast (TYPE_VPTR_BASETYPE (vfn_base), value);
 345   vtable_address
 346     = value_as_address (value_field (value, TYPE_VPTR_FIELDNO (vfn_base)));
 347
 348   vtable = value_at_lazy (vtable_type,
 349                           vtable_address - vtable_address_point_offset (),
 350                           VALUE_BFD_SECTION (value));
 351
 352   /* Fetch the appropriate function pointer from the vtable.  */
 353   vfn = value_subscript (value_field (vtable, vtable_field_virtual_functions),
 354                          value_from_longest (builtin_type_int,
 355                                              TYPE_FN_FIELD_VOFFSET (f, j)));
 356
 357   /* Cast the function pointer to the appropriate type.  */
 358   vfn = value_cast (lookup_pointer_type (TYPE_FN_FIELD_TYPE (f, j)),
 359                     vfn);
 360
 361   /* Is (type)value always numerically the same as (vfn_base)value?
 362      If so we can spare this cast and use one of the ones above.  */
 363   *value_p = value_addr (value_cast (type, *value_p));
 364
 365   return vfn;
 366 }
 367
 368 /* Compute the offset of the baseclass which is
 369    the INDEXth baseclass of class TYPE,
 370    for value at VALADDR (in host) at ADDRESS (in target).
 371    The result is the offset of the baseclass value relative
 372    to (the address of)(ARG) + OFFSET.
 373
 374    -1 is returned on error. */
 375 int
 376 gnuv3_baseclass_offset (struct type *type, int index, char *valaddr,
 377                         CORE_ADDR address)
 378 {
 379   struct type *vtable_type = gdbarch_data (current_gdbarch,
 380                                            vtable_type_gdbarch_data);
 381   struct value *vtable;
 382   struct type *vbasetype;
 383   struct value *offset_val, *vbase_array;
 384   CORE_ADDR vtable_address;
 385   long int cur_base_offset, base_offset;
 386
 387   /* If it isn't a virtual base, this is easy.  The offset is in the
 388      type definition.  */
 389   if (!BASETYPE_VIA_VIRTUAL (type, index))
 390     return TYPE_BASECLASS_BITPOS (type, index) / 8;
 391
 392   /* To access a virtual base, we need to use the vbase offset stored in
 393      our vtable.  Recent GCC versions provide this information.  If it isn't
 394      available, we could get what we needed from RTTI, or from drawing the
 395      complete inheritance graph based on the debug info.  Neither is
 396      worthwhile.  */
 397   cur_base_offset = TYPE_BASECLASS_BITPOS (type, index) / 8;
 398   if (cur_base_offset >= - vtable_address_point_offset ())
 399     error ("Expected a negative vbase offset (old compiler?)");
 400
 401   cur_base_offset = cur_base_offset + vtable_address_point_offset ();
 402   if ((- cur_base_offset) % TYPE_LENGTH (builtin_type_void_data_ptr) != 0)
 403     error ("Misaligned vbase offset.");
 404   cur_base_offset = cur_base_offset
 405     / ((int) TYPE_LENGTH (builtin_type_void_data_ptr));
 406
 407   /* We're now looking for the cur_base_offset'th entry (negative index)
 408      in the vcall_and_vbase_offsets array.  We used to cast the object to
 409      its TYPE_VPTR_BASETYPE, and reference the vtable as TYPE_VPTR_FIELDNO;
 410      however, that cast can not be done without calling baseclass_offset again
 411      if the TYPE_VPTR_BASETYPE is a virtual base class, as described in the
 412      v3 C++ ABI Section 2.4.I.2.b.  Fortunately the ABI guarantees that the
 413      vtable pointer will be located at the beginning of the object, so we can
 414      bypass the casting.  Verify that the TYPE_VPTR_FIELDNO is in fact at the
 415      start of whichever baseclass it resides in, as a sanity measure.  */
 416
 417   vbasetype = TYPE_VPTR_BASETYPE (type);
 418   if (TYPE_FIELD_BITPOS (vbasetype, TYPE_VPTR_FIELDNO (vbasetype)) != 0)
 419     error ("Illegal vptr offset in class %s",
 420            TYPE_NAME (vbasetype) ? TYPE_NAME (vbasetype) : "<unknown>");
 421
 422   vtable_address = value_as_address (value_at_lazy (builtin_type_void_data_ptr,
 423                                                     address, NULL));
 424   vtable = value_at_lazy (vtable_type,
 425                           vtable_address - vtable_address_point_offset (),
 426                           NULL);
 427   offset_val = value_from_longest(builtin_type_int, cur_base_offset);
 428   vbase_array = value_field (vtable, vtable_field_vcall_and_vbase_offsets);
 429   base_offset = value_as_long (value_subscript (vbase_array, offset_val));
 430   return base_offset;
 431 }
 432
 433 static void
 434 init_gnuv3_ops (void)
 435 {
 436   vtable_type_gdbarch_data = register_gdbarch_data (build_gdb_vtable_type, 0);
 437
 438   gnu_v3_abi_ops.shortname = "gnu-v3";
 439   gnu_v3_abi_ops.longname = "GNU G++ Version 3 ABI";
 440   gnu_v3_abi_ops.doc = "G++ Version 3 ABI";
 441   gnu_v3_abi_ops.is_destructor_name = is_gnu_v3_mangled_dtor;
 442   gnu_v3_abi_ops.is_constructor_name = is_gnu_v3_mangled_ctor;
 443   gnu_v3_abi_ops.is_vtable_name = gnuv3_is_vtable_name;
 444   gnu_v3_abi_ops.is_operator_name = gnuv3_is_operator_name;
 445   gnu_v3_abi_ops.rtti_type = gnuv3_rtti_type;
 446   gnu_v3_abi_ops.virtual_fn_field = gnuv3_virtual_fn_field;
 447   gnu_v3_abi_ops.baseclass_offset = gnuv3_baseclass_offset;
 448 }
 449
 450
 451 void
 452 _initialize_gnu_v3_abi (void)
 453 {
 454   init_gnuv3_ops ();
 455
 456   register_cp_abi (gnu_v3_abi_ops);
 457 }