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                           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   /* FIXME: chastain/2003-11-26: block=NULL is bogus.  See pr gdb/1465. */
 259   run_time_type = cp_lookup_rtti_type (class_name, NULL);
 260   if (run_time_type == NULL)
 261     return NULL;
 262
 263   /* Get the offset from VALUE to the top of the complete object.
 264      NOTE: this is the reverse of the meaning of *TOP_P.  */
 265   offset_to_top
 266     = value_as_long (value_field (vtable, vtable_field_offset_to_top));
 267
 268   if (full_p)
 269     *full_p = (- offset_to_top == VALUE_EMBEDDED_OFFSET (value)
 270                && (TYPE_LENGTH (VALUE_ENCLOSING_TYPE (value))
 271                    >= TYPE_LENGTH (run_time_type)));
 272   if (top_p)
 273     *top_p = - offset_to_top;
 274
 275   return run_time_type;
 276 }
 277
 278
 279 static struct value *
 280 gnuv3_virtual_fn_field (struct value **value_p,
 281                         struct fn_field *f, int j,
 282                         struct type *type, int offset)
 283 {
 284   struct type *vtable_type = gdbarch_data (current_gdbarch,
 285                                            vtable_type_gdbarch_data);
 286   struct value *value = *value_p;
 287   struct type *value_type = check_typedef (VALUE_TYPE (value));
 288   struct type *vfn_base;
 289   CORE_ADDR vtable_address;
 290   struct value *vtable;
 291   struct value *vfn;
 292
 293   /* Some simple sanity checks.  */
 294   if (TYPE_CODE (value_type) != TYPE_CODE_CLASS)
 295     error ("Only classes can have virtual functions.");
 296
 297   /* Find the base class that defines this virtual function.  */
 298   vfn_base = TYPE_FN_FIELD_FCONTEXT (f, j);
 299   if (! vfn_base)
 300     /* In programs compiled with G++ version 1, the debug info doesn't
 301        say which base class defined the virtual function.  We'll guess
 302        it's the same base class that has our vtable; this is wrong for
 303        multiple inheritance, but it's better than nothing.  */
 304     vfn_base = TYPE_VPTR_BASETYPE (type);
 305
 306   /* This type may have been defined before its virtual function table
 307      was.  If so, fill in the virtual function table entry for the
 308      type now.  */
 309   if (TYPE_VPTR_FIELDNO (vfn_base) < 0)
 310     fill_in_vptr_fieldno (vfn_base);
 311   if (TYPE_VPTR_FIELDNO (vfn_base) < 0)
 312     error ("Could not find virtual table pointer for class \"%s\".",
 313            TYPE_TAG_NAME (vfn_base) ? TYPE_TAG_NAME (vfn_base) : "<unknown>");
 314
 315   /* Now that we know which base class is defining our virtual
 316      function, cast our value to that baseclass.  This takes care of
 317      any necessary `this' adjustments.  */
 318   if (vfn_base != value_type)
 319     value = value_cast (vfn_base, value);
 320
 321   /* Now value is an object of the appropriate base type.  Fetch its
 322      virtual table.  */
 323   /* It might be possible to do this cast at the same time as the above.
 324      Does multiple inheritance affect this?
 325      Can this even trigger, or is TYPE_VPTR_BASETYPE idempotent?
 326   */
 327   if (TYPE_VPTR_BASETYPE (vfn_base) != vfn_base)
 328     value = value_cast (TYPE_VPTR_BASETYPE (vfn_base), value);
 329   vtable_address
 330     = value_as_address (value_field (value, TYPE_VPTR_FIELDNO (vfn_base)));
 331
 332   vtable = value_at_lazy (vtable_type,
 333                           vtable_address - vtable_address_point_offset (),
 334                           VALUE_BFD_SECTION (value));
 335
 336   /* Fetch the appropriate function pointer from the vtable.  */
 337   vfn = value_subscript (value_field (vtable, vtable_field_virtual_functions),
 338                          value_from_longest (builtin_type_int,
 339                                              TYPE_FN_FIELD_VOFFSET (f, j)));
 340
 341   /* Cast the function pointer to the appropriate type.  */
 342   vfn = value_cast (lookup_pointer_type (TYPE_FN_FIELD_TYPE (f, j)),
 343                     vfn);
 344
 345   /* Is (type)value always numerically the same as (vfn_base)value?
 346      If so we can spare this cast and use one of the ones above.  */
 347   *value_p = value_addr (value_cast (type, *value_p));
 348
 349   return vfn;
 350 }
 351
 352 /* Compute the offset of the baseclass which is
 353    the INDEXth baseclass of class TYPE,
 354    for value at VALADDR (in host) at ADDRESS (in target).
 355    The result is the offset of the baseclass value relative
 356    to (the address of)(ARG) + OFFSET.
 357
 358    -1 is returned on error. */
 359 static int
 360 gnuv3_baseclass_offset (struct type *type, int index, char *valaddr,
 361                         CORE_ADDR address)
 362 {
 363   struct type *vtable_type = gdbarch_data (current_gdbarch,
 364                                            vtable_type_gdbarch_data);
 365   struct value *vtable;
 366   struct type *vbasetype;
 367   struct value *offset_val, *vbase_array;
 368   CORE_ADDR vtable_address;
 369   long int cur_base_offset, base_offset;
 370
 371   /* If it isn't a virtual base, this is easy.  The offset is in the
 372      type definition.  */
 373   if (!BASETYPE_VIA_VIRTUAL (type, index))
 374     return TYPE_BASECLASS_BITPOS (type, index) / 8;
 375
 376   /* To access a virtual base, we need to use the vbase offset stored in
 377      our vtable.  Recent GCC versions provide this information.  If it isn't
 378      available, we could get what we needed from RTTI, or from drawing the
 379      complete inheritance graph based on the debug info.  Neither is
 380      worthwhile.  */
 381   cur_base_offset = TYPE_BASECLASS_BITPOS (type, index) / 8;
 382   if (cur_base_offset >= - vtable_address_point_offset ())
 383     error ("Expected a negative vbase offset (old compiler?)");
 384
 385   cur_base_offset = cur_base_offset + vtable_address_point_offset ();
 386   if ((- cur_base_offset) % TYPE_LENGTH (builtin_type_void_data_ptr) != 0)
 387     error ("Misaligned vbase offset.");
 388   cur_base_offset = cur_base_offset
 389     / ((int) TYPE_LENGTH (builtin_type_void_data_ptr));
 390
 391   /* We're now looking for the cur_base_offset'th entry (negative index)
 392      in the vcall_and_vbase_offsets array.  We used to cast the object to
 393      its TYPE_VPTR_BASETYPE, and reference the vtable as TYPE_VPTR_FIELDNO;
 394      however, that cast can not be done without calling baseclass_offset again
 395      if the TYPE_VPTR_BASETYPE is a virtual base class, as described in the
 396      v3 C++ ABI Section 2.4.I.2.b.  Fortunately the ABI guarantees that the
 397      vtable pointer will be located at the beginning of the object, so we can
 398      bypass the casting.  Verify that the TYPE_VPTR_FIELDNO is in fact at the
 399      start of whichever baseclass it resides in, as a sanity measure - iff
 400      we have debugging information for that baseclass.  */
 401
 402   vbasetype = TYPE_VPTR_BASETYPE (type);
 403   if (TYPE_VPTR_FIELDNO (vbasetype) < 0)
 404     fill_in_vptr_fieldno (vbasetype);
 405
 406   if (TYPE_VPTR_FIELDNO (vbasetype) >= 0
 407       && TYPE_FIELD_BITPOS (vbasetype, TYPE_VPTR_FIELDNO (vbasetype)) != 0)
 408     error ("Illegal vptr offset in class %s",
 409            TYPE_NAME (vbasetype) ? TYPE_NAME (vbasetype) : "<unknown>");
 410
 411   vtable_address = value_as_address (value_at_lazy (builtin_type_void_data_ptr,
 412                                                     address, NULL));
 413   vtable = value_at_lazy (vtable_type,
 414                           vtable_address - vtable_address_point_offset (),
 415                           NULL);
 416   offset_val = value_from_longest(builtin_type_int, cur_base_offset);
 417   vbase_array = value_field (vtable, vtable_field_vcall_and_vbase_offsets);
 418   base_offset = value_as_long (value_subscript (vbase_array, offset_val));
 419   return base_offset;
 420 }
 421
 422 static void
 423 init_gnuv3_ops (void)
 424 {
 425   vtable_type_gdbarch_data = gdbarch_data_register_post_init (build_gdb_vtable_type);
 426
 427   gnu_v3_abi_ops.shortname = "gnu-v3";
 428   gnu_v3_abi_ops.longname = "GNU G++ Version 3 ABI";
 429   gnu_v3_abi_ops.doc = "G++ Version 3 ABI";
 430   gnu_v3_abi_ops.is_destructor_name = is_gnu_v3_mangled_dtor;
 431   gnu_v3_abi_ops.is_constructor_name = is_gnu_v3_mangled_ctor;
 432   gnu_v3_abi_ops.is_vtable_name = gnuv3_is_vtable_name;
 433   gnu_v3_abi_ops.is_operator_name = gnuv3_is_operator_name;
 434   gnu_v3_abi_ops.rtti_type = gnuv3_rtti_type;
 435   gnu_v3_abi_ops.virtual_fn_field = gnuv3_virtual_fn_field;
 436   gnu_v3_abi_ops.baseclass_offset = gnuv3_baseclass_offset;
 437 }
 438
 439 extern initialize_file_ftype _initialize_gnu_v3_abi; /* -Wmissing-prototypes */
 440
 441 void
 442 _initialize_gnu_v3_abi (void)
 443 {
 444   init_gnuv3_ops ();
 445
 446   register_cp_abi (&gnu_v3_abi_ops);
 447 }