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Re: Handling of c++ function members
On Mon, 2011-09-26 at 23:00 +0200, Joost van der Sluis wrote:
> On Mon, 2011-09-26 at 16:38 -0400, Daniel Jacobowitz wrote:
> > On Mon, Sep 26, 2011 at 12:46 PM, Joost van der Sluis <firstname.lastname@example.org> wrote:
> > Can you be a little more specific, maybe an example?
> What I understood is, that DW_AT_vtable_elem_location should contain a
> Dwarf-block that calculates the location of a pointer in which the
> location of the function member is stored.
If you need an example, you can compile the wikipedia
virtual-function-example (after fixing compilation by adding the
declaration of 'it') http://en.wikipedia.org/wiki/Virtual_function
objdump -W of the function 'eat' in that example:
<1><1902>: Abbrev Number: 66 (DW_TAG_class_type)
<1903> DW_AT_name : (indirect string, offset: 0x17e6): Animal
<1907> DW_AT_byte_size : 8
<1908> DW_AT_decl_file : 2
<1909> DW_AT_decl_line : 4
<190a> DW_AT_containing_type: <0x1902>
<190e> DW_AT_sibling : <0x19be>
<2><1953>: Abbrev Number: 69 (DW_TAG_subprogram)
<1954> DW_AT_external : 1
<1955> DW_AT_name : eat
<1959> DW_AT_decl_file : 2
<195a> DW_AT_decl_line : 6
<195b> DW_AT_MIPS_linkage_name: (indirect string, offset: 0xad3): _ZNK6Animal3eatEv
<195f> DW_AT_virtuality : 1 (virtual)
<1960> DW_AT_vtable_elem_location: 2 byte block: 10 0 (DW_OP_constu: 0)
<1963> DW_AT_containing_type: <0x1902>
<1967> DW_AT_accessibility: 1 (public)
<1968> DW_AT_declaration : 1
<1969> DW_AT_object_pointer: <0x1971>
<196d> DW_AT_sibling : <0x1978>
<3><1971>: Abbrev Number: 25 (DW_TAG_formal_parameter)
<1972> DW_AT_type : <0x2a55>
<1976> DW_AT_artificial : 1
> But it seems to me that gcc stores the index of the function member
> within some vtable in DW_AT_vtable_elem_location, instead of the memory
> address itself. In gnu-v2-abi.c there is some code that 'knows' how this
> vtable is organized so it is able to calculate the location of the
> And there are two thing's I'm not sure about: gcc stores
> DW_AT_containing_type in the debug-info, with the 'parent' entry of the
> DW_TAG_subprogram entry. To me it looks that this is duplicated
> information, and not specified in the Dwarf-specs. Secondly I do not
> understand where the DW_AT_object_pointer is used for?
DW_AT_containing_type is placed into NFN's Context field by dwarf2read.
Joost van der Sluis.