From: Josh Stone <jistone@redhat.com>
To: elfutils-devel@lists.fedorahosted.org
Subject: Re: dwarf_aggregate_size() seems to fall over on pointer types
Date: Wed, 01 Oct 2014 10:46:52 -0700 [thread overview]
Message-ID: <542C3E0C.3000503@redhat.com> (raw)
In-Reply-To: CAG6CVpW-0N9-b+xEax5cuowKTxAKwDntyUB-haaZPmpM3q28FA@mail.gmail.com
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On 10/01/2014 10:15 AM, Conrad Rad wrote:
> Hi all,
>
> First, I'm not super familiar with DWARF, and perhaps this is a bug in
> the DWARF information emitted by Clang (3.4). It's definitely a
> difference between GCC and Clang DWARF output.
>
> I've been fiddling with a pahole-alike tool[0] that sits directly on
> elfutils (as opposed to libdwarves, which hasn't been updated for some
> time and doesn't handle some of the tags Clang emits). I've observed
> that dwarf_aggregate_size() doesn't seem to like types that are
> pointers or arrays of pointers[1].
>
> 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.)
next reply other threads:[~2014-10-01 17:46 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-01 17:46 Josh Stone [this message]
-- strict thread matches above, loose matches on Subject: below --
2014-10-02 20:56 Mark Wielaard
2014-10-02 12:50 Conrad Rad
2014-10-02 12:05 Mark Wielaard
2014-10-01 20:33 Roland McGrath
2014-10-01 19:26 Conrad Rad
2014-10-01 19:23 Conrad Rad
2014-10-01 19:10 Conrad Rad
2014-10-01 18:47 Josh Stone
2014-10-01 18:34 Conrad Rad
2014-10-01 18:33 Mark Wielaard
2014-10-01 17:15 Conrad Rad
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