This is the mail archive of the
gdb@sources.redhat.com
mailing list for the GDB project.
Re: C++ debugging progress
>>>>> "Jason" == Jason Merrill <jason@redhat.com> writes:
> Yep. Since Base is a virtual base of Left, the DW_AT_data_member_location
> here should be a complex expression telling the debugger to go through the
> vtable. I'll get on it.
> I'll also change the stabs output to give the offset within the vtable
> rather than the offset of the base in a complete object; gdb will still
> need to be clever enough to know what to do with it.
Please give this a spin; gdb doesn't like it, but I think it's correct.
Note that the offset given in the stabs output should be treated as
negative, so for V3 objects,
BaseAddr = LeftAddr + *((*LeftAddr) - Offset)
The dwarf2 output is the above encoded in reverse Polish notation. I
suppose we could rely on gdb to know the equation for dwarf, too, but that
would be nonconforming and only saves four bytes.
2001-11-28 Jason Merrill <jason@redhat.com>
* dwarf2out.c (add_data_member_location_attribute): Do the
right thing for virtual bases.
* dbxout.c (dbxout_type): For a virtual base, print the offset
within the vtable.
*** dwarf2out.c.~1~ Fri Nov 23 17:27:50 2001
--- dwarf2out.c Wed Nov 28 20:42:37 2001
*************** add_data_member_location_attribute (die,
*** 8407,8434 ****
dw_die_ref die;
tree decl;
{
! unsigned long offset;
! dw_loc_descr_ref loc_descr;
! enum dwarf_location_atom op;
if (TREE_CODE (decl) == TREE_VEC)
! offset = tree_low_cst (BINFO_OFFSET (decl), 0);
else
offset = field_byte_offset (decl);
! /* The DWARF2 standard says that we should assume that the structure address
! is already on the stack, so we can specify a structure field address
! by using DW_OP_plus_uconst. */
#ifdef MIPS_DEBUGGING_INFO
! /* ??? The SGI dwarf reader does not handle the DW_OP_plus_uconst operator
! correctly. It works only if we leave the offset on the stack. */
! op = DW_OP_constu;
#else
! op = DW_OP_plus_uconst;
#endif
! loc_descr = new_loc_descr (op, offset, 0);
add_AT_loc (die, DW_AT_data_member_location, loc_descr);
}
--- 8407,8471 ----
dw_die_ref die;
tree decl;
{
! long offset;
! dw_loc_descr_ref loc_descr = 0;
if (TREE_CODE (decl) == TREE_VEC)
! {
! /* We're working on the TAG_inheritance for a base class. */
!
! if (TREE_VIA_VIRTUAL (decl))
! {
! /* For C++ virtual bases we can't just use BINFO_OFFSET, as they
! aren't at a fixed offset from all (sub)objects of the same type.
! We need to extract the appropriate offset from our vtable. */
!
! dw_loc_descr_ref tmp;
! /* Make a copy of the object address. */
! tmp = new_loc_descr (DW_OP_dup, 0, 0);
! add_loc_descr (&loc_descr, tmp);
! /* Extract the vtable address. */
! tmp = new_loc_descr (DW_OP_deref, 0, 0);
! add_loc_descr (&loc_descr, tmp);
! /* Calculate the address of the offset. */
! offset = tree_low_cst (BINFO_VPTR_FIELD (decl), 0);
! if (offset >= 0)
! abort ();
! tmp = int_loc_descriptor (-offset);
! add_loc_descr (&loc_descr, tmp);
! tmp = new_loc_descr (DW_OP_minus, 0, 0);
! add_loc_descr (&loc_descr, tmp);
! /* Extract the offset. */
! tmp = new_loc_descr (DW_OP_deref, 0, 0);
! add_loc_descr (&loc_descr, tmp);
! /* Add it to the object address. */
! tmp = new_loc_descr (DW_OP_plus, 0, 0);
! add_loc_descr (&loc_descr, tmp);
! }
! else
! offset = tree_low_cst (BINFO_OFFSET (decl), 0);
! }
else
offset = field_byte_offset (decl);
! if (! loc_descr)
! {
! enum dwarf_location_atom op;
!
! /* The DWARF2 standard says that we should assume that the structure address
! is already on the stack, so we can specify a structure field address
! by using DW_OP_plus_uconst. */
#ifdef MIPS_DEBUGGING_INFO
! /* ??? The SGI dwarf reader does not handle the DW_OP_plus_uconst operator
! correctly. It works only if we leave the offset on the stack. */
! op = DW_OP_constu;
#else
! op = DW_OP_plus_uconst;
#endif
! loc_descr = new_loc_descr (op, offset, 0);
! }
add_AT_loc (die, DW_AT_data_member_location, loc_descr);
}
*** dbxout.c.~1~ Thu Nov 15 16:59:31 2001
--- dbxout.c Wed Nov 28 20:49:04 2001
*************** dbxout_type (type, full)
*** 1492,1499 ****
putc (TREE_VIA_VIRTUAL (child) ? '1' : '0', asmfile);
putc (TREE_VIA_PUBLIC (child) ? '2' : '0', asmfile);
CHARS (2);
! print_wide_int (tree_low_cst (BINFO_OFFSET (child), 0)
! * BITS_PER_UNIT);
putc (',', asmfile);
CHARS (1);
dbxout_type (BINFO_TYPE (child), 0);
--- 1492,1506 ----
putc (TREE_VIA_VIRTUAL (child) ? '1' : '0', asmfile);
putc (TREE_VIA_PUBLIC (child) ? '2' : '0', asmfile);
CHARS (2);
! if (TREE_VIA_VIRTUAL (child))
! /* For a virtual base, print the (negative) offset within
! the vtable where we must look to find the necessary
! adjustment. */
! print_wide_int (-tree_low_cst (BINFO_VPTR_FIELD (child), 0)
! * BITS_PER_UNIT);
! else
! print_wide_int (tree_low_cst (BINFO_OFFSET (child), 0)
! * BITS_PER_UNIT);
putc (',', asmfile);
CHARS (1);
dbxout_type (BINFO_TYPE (child), 0);