On Mon, Feb 28, 2022 at 12:55 PM Greg Clayton via Dwarf-Discuss < dwarf-discuss@lists.dwarfstd.org> wrote:
> > > On Feb 28, 2022, at 5:49 AM, Ron Louzon via Dwarf-Discuss < > dwarf-discuss@lists.dwarfstd.org> wrote: > > I have an application which uses DwarfLib to extract type information from > debug executable images. I have found in the DWARF data that some > structure types have a "virtual" pointer added as their first member and > this pointer's DIE contains the tag DW_AT_artificial=true. How does that > pointer member affect the offsets of the members that follow it in the > structure. > > > This will cause all other members to be pushed out by a pointer size. > > Should this 4-byte pointer be ignored or will its size cause the other > structure members to be pushed out in memory by 4 bytes? > > > All offsets in the DWARF should be correct for all members, including > artificial members and any members that follow it in memory. So yes, if > there is a vtable pointer added as the first member, its offset and all > other offsets will be correct, so there is no need to adjust anything when > reading this data. > > You could choose to not show this, but I find it is often easier to show > this information in case some compiler change in the future marks something > that you might want to see as artificial. For example the "this" parameter > to C++ methods is marked as artificial, and people do want to see the > "this" in the variables view. Granted that is a variable vs a member > variable. > Probably the important distinction there is that "this", while artificial, is named/usable in the source whereas the vtable isn't. Either having some DWARF attribute to communicate that distinction, or a workaround might be to detect that the vtable name uses a reserved identifier could be good - I guess the reality is that DWARF consumers probably hardcode some sort of "this is the vtable pointer" -o so maybe we should have some DWARF attribute that communicates that, instead of relying on the string name of the member? Not sure.
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