Re: dwarf_aggregate_size() seems to fall over on pointer types

[Conrad Rad <cse dot cem at gmail dot com>]

On Wed, Oct 1, 2014 at 1:46 PM, Josh Stone <jistone@redhat.com> wrote:
> On 10/01/2014 10:15 AM, Conrad Rad wrote:
>> I've compiled a small example program, repro, and output[2]:
>> http://pastie.org/9610702
>>
>> dwarf_aggregate_size() has no trouble with most member types, or even
>> pointer types on the output from GCC. However, it returns an error on
>> Clang's output.
>>
>> Perhaps Clang is just eliding pointer size information, assuming
>> consumers will consult the Elf machine class and infer?
>
> Indeed, clang doesn't seem to output DW_AT_byte_size on any
> DW_TAG_pointer_type, but gcc does.
>
> FWIW, the DWARF4 Appendix A does *not* list DW_AT_byte_size as being
> applicable to DW_TAG_pointer_type, nor DW_TAG_reference_type, nor
> DW_TAG_rvalue_reference_type.  However, that is just "informative", and
> producers are free to omit some of the suggestions as well as add their
> own, so it's not an error that gcc produces DW_AT_byte_size.
>
>> Am I missing something? Is this a Clang bug or an elfutils bug?
>
> I don't think it's strictly a bug in either.  Clang is not required to
> produce byte_size, and elfutils is just reporting what it knows.
>
> Still, it might be nice if elfutils made that machine-class inference
> for you.  (But I worry about things like that mips pointer issue
> reported recently.)

It'd be nice. If it's just pointers and arrays of pointers, I can
cobble a fallback together. Members that have struct types with
pointer members should get their own size information emitted by both
compilers, I guess? (Both generate size information for 'struct b'.)

What was the issue with MIPS pointers, by the way?

Thanks,
Conrad