dblaikie added a comment. In D101237#2728726 <https://reviews.llvm.org/D101237#2728726>, @teemperor wrote:
>> (and it could tell clang exactly how large the structure is too - from the >> DWARF) > > We are actually doing that to my knowledge and return the `DW_AT_byte_size` > value for the record type. The relevant API that LLDB implements to get > layout/size info back to Clang is: > > bool layoutRecordType( > const clang::RecordDecl *Record, uint64_t &Size, uint64_t &Alignment, > llvm::DenseMap<const clang::FieldDecl *, uint64_t> &FieldOffsets, > llvm::DenseMap<const clang::CXXRecordDecl *, clang::CharUnits> > &BaseOffsets, > llvm::DenseMap<const clang::CXXRecordDecl *, clang::CharUnits> > &VirtualBaseOffsets) override; > > I think the `sizeof` part actually works* in this regard as we just return > whatever we got from DWARF. I get the correct results for the example above > (both with and without this patch). There might be some weirder corner cases > that could go wrong but I think the main concern are more complicated > situations like in the crash that is fixed here. > > FWIW, I took a look at the DWARF standard and I think that is actually > something we should already emit in the form of a `DW_AT_byte_size 0` > attribute at the field? Quote: > > If the size of a data member is not the same as the size of the type given > for the data member, the data member has either a DW_AT_byte_size or a > DW_AT_bit_size attribute whose integer constant value (see Section 2.19) is > the amount of storage needed to hold the value of the data member. > > I am not a DWARF laywer so maybe I understand that part wrong. > > (*I actually found a bug that miscalculated empty structs while testing, but > that's unrelated. Patch incoming). Hmm, sounds sort of plausible - but might not be right. The cppreference article on no_unique_address presents some interesting challenges that will be maybe surprising (well, I guess not, given the need to render these situations for empty bases already) - yeah, I guess probably the question to ask is: How are empty bases rendered today? I think the trick is they're rendered not as zero length, but as having a location that overlaps with another field - and having a length of 1 (which is the real length of the "empty" object). Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D101237/new/ https://reviews.llvm.org/D101237 _______________________________________________ lldb-commits mailing list lldb-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-commits
