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/* Abstraction of GNU v2 abi.
Copyright (C) 2001-2021 Free Software Foundation, Inc.
Contributed by Daniel Berlin <>
This file is part of GDB.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <>. */
#include "defs.h"
#include "symtab.h"
#include "gdbtypes.h"
#include "value.h"
#include "demangle.h"
#include "gdb-demangle.h"
#include "cp-abi.h"
#include "cp-support.h"
#include <ctype.h>
static cp_abi_ops gnu_v2_abi_ops;
static int vb_match (struct type *, int, struct type *);
static enum dtor_kinds
gnuv2_is_destructor_name (const char *name)
if ((name[0] == '_' && is_cplus_marker (name[1]) && name[2] == '_')
|| startswith (name, "__dt__"))
return complete_object_dtor;
return (enum dtor_kinds) 0;
static enum ctor_kinds
gnuv2_is_constructor_name (const char *name)
if ((name[0] == '_' && name[1] == '_'
&& (isdigit (name[2]) || strchr ("Qt", name[2])))
|| startswith (name, "__ct__"))
return complete_object_ctor;
return (enum ctor_kinds) 0;
static int
gnuv2_is_vtable_name (const char *name)
return (((name)[0] == '_'
&& (((name)[1] == 'V' && (name)[2] == 'T')
|| ((name)[1] == 'v' && (name)[2] == 't'))
&& is_cplus_marker ((name)[3])) ||
((name)[0] == '_' && (name)[1] == '_'
&& (name)[2] == 'v' && (name)[3] == 't' && (name)[4] == '_'));
static int
gnuv2_is_operator_name (const char *name)
return startswith (name, CP_OPERATOR_STR);
/* Return a virtual function as a value.
ARG1 is the object which provides the virtual function
table pointer. *ARG1P is side-effected in calling this function.
F is the list of member functions which contains the desired virtual
J is an index into F which provides the desired virtual function.
TYPE is the type in which F is located. */
static struct value *
gnuv2_virtual_fn_field (struct value **arg1p, struct fn_field * f, int j,
struct type * type, int offset)
struct value *arg1 = *arg1p;
struct type *type1 = check_typedef (value_type (arg1));
struct type *entry_type;
/* First, get the virtual function table pointer. That comes
with a strange type, so cast it to type `pointer to long' (which
should serve just fine as a function type). Then, index into
the table, and convert final value to appropriate function type. */
struct value *entry;
struct value *vfn;
struct value *vtbl;
struct type *fcontext = TYPE_FN_FIELD_FCONTEXT (f, j);
struct type *context;
struct type *context_vptr_basetype;
int context_vptr_fieldno;
if (fcontext == NULL)
/* We don't have an fcontext (e.g. the program was compiled with
g++ version 1). Try to get the vtbl from the TYPE_VPTR_BASETYPE.
This won't work right for multiple inheritance, but at least we
should do as well as GDB 3.x did. */
fcontext = TYPE_VPTR_BASETYPE (type);
context = lookup_pointer_type (fcontext);
/* Now context is a pointer to the basetype containing the vtbl. */
if (TYPE_TARGET_TYPE (context) != type1)
struct value *tmp = value_cast (context, value_addr (arg1));
arg1 = value_ind (tmp);
type1 = check_typedef (value_type (arg1));
context = type1;
/* Now context is the basetype containing the vtbl. */
/* This type may have been defined before its virtual function table
was. If so, fill in the virtual function table entry for the
type now. */
context_vptr_fieldno = get_vptr_fieldno (context, &context_vptr_basetype);
/* FIXME: What to do if vptr_fieldno is still -1? */
/* The virtual function table is now an array of structures
which have the form { int16 offset, delta; void *pfn; }. */
vtbl = value_primitive_field (arg1, 0, context_vptr_fieldno,
/* With older versions of g++, the vtbl field pointed to an array
of structures. Nowadays it points directly to the structure. */
if (value_type (vtbl)->code () == TYPE_CODE_PTR
&& TYPE_TARGET_TYPE (value_type (vtbl))->code () == TYPE_CODE_ARRAY)
/* Handle the case where the vtbl field points to an
array of structures. */
vtbl = value_ind (vtbl);
/* Index into the virtual function table. This is hard-coded because
looking up a field is not cheap, and it may be important to save
time, e.g. if the user has set a conditional breakpoint calling
a virtual function. */
entry = value_subscript (vtbl, vi);
/* Handle the case where the vtbl field points directly to a
structure. */
vtbl = value_ptradd (vtbl, vi);
entry = value_ind (vtbl);
entry_type = check_typedef (value_type (entry));
if (entry_type->code () == TYPE_CODE_STRUCT)
/* Move the `this' pointer according to the virtual function table. */
set_value_offset (arg1, value_offset (arg1)
+ value_as_long (value_field (entry, 0)));
if (!value_lazy (arg1))
set_value_lazy (arg1, 1);
value_fetch_lazy (arg1);
vfn = value_field (entry, 2);
else if (entry_type->code () == TYPE_CODE_PTR)
vfn = entry;
error (_("I'm confused: virtual function table has bad type"));
/* Reinstantiate the function pointer with the correct type. */
deprecated_set_value_type (vfn,
lookup_pointer_type (TYPE_FN_FIELD_TYPE (f, j)));
*arg1p = arg1;
return vfn;
static struct type *
gnuv2_value_rtti_type (struct value *v, int *full, LONGEST *top, int *using_enc)
struct type *known_type;
struct type *rtti_type;
struct bound_minimal_symbol minsym;
char *p;
const char *linkage_name;
struct type *btype;
struct type *known_type_vptr_basetype;
int known_type_vptr_fieldno;
if (full)
*full = 0;
if (top)
*top = -1;
if (using_enc)
*using_enc = 0;
/* Get declared type. */
known_type = value_type (v);
known_type = check_typedef (known_type);
/* RTTI works only or class objects. */
if (known_type->code () != TYPE_CODE_STRUCT)
return NULL;
/* Plan on this changing in the future as i get around to setting
the vtables properly for G++ compiled stuff. Also, I'll be using
the type info functions, which are always right. Deal with it
until then. */
/* Try to get the vptr basetype, fieldno. */
known_type_vptr_fieldno = get_vptr_fieldno (known_type,
/* If we can't find it, give up. */
if (known_type_vptr_fieldno < 0)
return NULL;
/* Make sure our basetype and known type match, otherwise, cast
so we can get at the vtable properly. */
btype = known_type_vptr_basetype;
btype = check_typedef (btype);
if (btype != known_type )
v = value_cast (btype, v);
if (using_enc)
/* We can't use value_ind here, because it would want to use RTTI, and
we'd waste a bunch of time figuring out we already know the type.
Besides, we don't care about the type, just the actual pointer. */
if (value_address (value_field (v, known_type_vptr_fieldno)) == 0)
return NULL;
vtbl = value_as_address (value_field (v, known_type_vptr_fieldno));
/* Try to find a symbol that is the vtable. */
if (minsym.minsym==NULL
|| (linkage_name=minsym.minsym->linkage_name ())==NULL
|| !is_vtable_name (linkage_name))
return NULL;
/* If we just skip the prefix, we get screwed by namespaces. */
gdb::unique_xmalloc_ptr<char> demangled_name
= gdb_demangle(linkage_name,DMGL_PARAMS|DMGL_ANSI);
p = strchr (demangled_name.get (), ' ');
if (p)
*p = '\0';
/* Lookup the type for the name. */
/* FIXME: chastain/2003-11-26: block=NULL is bogus. See pr gdb/1465. */
rtti_type = cp_lookup_rtti_type (demangled_name.get (), NULL);
if (rtti_type == NULL)
return NULL;
if (TYPE_N_BASECLASSES(rtti_type) > 1 && full && (*full) != 1)
if (top)
*top = TYPE_BASECLASS_BITPOS (rtti_type,
TYPE_VPTR_FIELDNO(rtti_type)) / 8;
if (top && ((*top) >0))
if (TYPE_LENGTH(rtti_type) > TYPE_LENGTH(known_type))
if (full)
if (full)
if (full)
return rtti_type;
/* Return true if the INDEXth field of TYPE is a virtual baseclass
pointer which is for the base class whose type is BASECLASS. */
static int
vb_match (struct type *type, int index, struct type *basetype)
struct type *fieldtype;
const char *name = type->field (index).name ();
const char *field_class_name = NULL;
if (*name != '_')
return 0;
/* gcc 2.4 uses _vb$. */
if (name[1] == 'v' && name[2] == 'b' && is_cplus_marker (name[3]))
field_class_name = name + 4;
/* gcc 2.5 will use __vb_. */
if (name[1] == '_' && name[2] == 'v' && name[3] == 'b' && name[4] == '_')
field_class_name = name + 5;
if (field_class_name == NULL)
/* This field is not a virtual base class pointer. */
return 0;
/* It's a virtual baseclass pointer, now we just need to find out whether
it is for this baseclass. */
fieldtype = type->field (index).type ();
if (fieldtype == NULL
|| fieldtype->code () != TYPE_CODE_PTR)
/* "Can't happen". */
return 0;
/* What we check for is that either the types are equal (needed for
nameless types) or have the same name. This is ugly, and a more
elegant solution should be devised (which would probably just push
the ugliness into symbol reading unless we change the stabs format). */
if (TYPE_TARGET_TYPE (fieldtype) == basetype)
return 1;
if (basetype->name () != NULL
&& TYPE_TARGET_TYPE (fieldtype)->name () != NULL
&& strcmp (basetype->name (),
TYPE_TARGET_TYPE (fieldtype)->name ()) == 0)
return 1;
return 0;
/* Compute the offset of the baseclass which is the INDEXth baseclass
of class TYPE, for value at VALADDR (in host) at ADDRESS (in
target). The result is the offset of the baseclass value relative
to (the address of)(ARG) + OFFSET. */
static int
gnuv2_baseclass_offset (struct type *type, int index,
const bfd_byte *valaddr, LONGEST embedded_offset,
CORE_ADDR address, const struct value *val)
struct type *basetype = TYPE_BASECLASS (type, index);
if (BASETYPE_VIA_VIRTUAL (type, index))
/* Must hunt for the pointer to this virtual baseclass. */
int i, len = type->num_fields ();
int n_baseclasses = TYPE_N_BASECLASSES (type);
/* First look for the virtual baseclass pointer
in the fields. */
for (i = n_baseclasses; i < len; i++)
if (vb_match (type, i, basetype))
struct type *field_type;
LONGEST field_offset;
int field_length;
field_type = check_typedef (type->field (i).type ());
field_offset = TYPE_FIELD_BITPOS (type, i) / 8;
field_length = TYPE_LENGTH (field_type);
if (!value_bytes_available (val, embedded_offset + field_offset,
_("Virtual baseclass pointer is not available"));
addr = unpack_pointer (field_type,
valaddr + embedded_offset + field_offset);
return addr - (LONGEST) address + embedded_offset;
/* Not in the fields, so try looking through the baseclasses. */
for (i = index + 1; i < n_baseclasses; i++)
/* Don't go through baseclass_offset, as that wraps
exceptions, thus, inner exceptions would be wrapped more
than once. */
int boffset =
gnuv2_baseclass_offset (type, i, valaddr,
embedded_offset, address, val);
if (boffset)
return boffset;
error (_("Baseclass offset not found"));
/* Baseclass is easily computed. */
return TYPE_BASECLASS_BITPOS (type, index) / 8;
static void
init_gnuv2_ops (void)
gnu_v2_abi_ops.shortname = "gnu-v2";
gnu_v2_abi_ops.longname = "GNU G++ Version 2 ABI";
gnu_v2_abi_ops.doc = "G++ Version 2 ABI";
gnu_v2_abi_ops.is_destructor_name = gnuv2_is_destructor_name;
gnu_v2_abi_ops.is_constructor_name = gnuv2_is_constructor_name;
gnu_v2_abi_ops.is_vtable_name = gnuv2_is_vtable_name;
gnu_v2_abi_ops.is_operator_name = gnuv2_is_operator_name;
gnu_v2_abi_ops.virtual_fn_field = gnuv2_virtual_fn_field;
gnu_v2_abi_ops.rtti_type = gnuv2_value_rtti_type;
gnu_v2_abi_ops.baseclass_offset = gnuv2_baseclass_offset;
void _initialize_gnu_v2_abi ();
_initialize_gnu_v2_abi ()
init_gnuv2_ops ();
register_cp_abi (&gnu_v2_abi_ops);