> On Feb 28, 2022, at 1:11 PM, David Blaikie via Dwarf-Discuss > <dwarf-discuss@lists.dwarfstd.org> wrote: > > > > On Mon, Feb 28, 2022 at 12:55 PM Greg Clayton via Dwarf-Discuss > <dwarf-discuss@lists.dwarfstd.org <mailto:dwarf-discuss@lists.dwarfstd.org>> > wrote: > > >> On Feb 28, 2022, at 5:49 AM, Ron Louzon via Dwarf-Discuss >> <dwarf-discuss@lists.dwarfstd.org <mailto: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.
Sounds interesting, yes. Maybe a DW_AT_language_runtime attribute? This could let people know that the item is part of the language runtime and not necessarily something the user would always want to see. > _______________________________________________ > Dwarf-Discuss mailing list > Dwarf-Discuss@lists.dwarfstd.org <mailto:Dwarf-Discuss@lists.dwarfstd.org> > http://lists.dwarfstd.org/listinfo.cgi/dwarf-discuss-dwarfstd.org > <http://lists.dwarfstd.org/listinfo.cgi/dwarf-discuss-dwarfstd.org>
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