[llvm-dev] [yaml2obj] GSoC-20: Add DWARF support to yaml2obj

David Blaikie via llvm-dev llvm-dev at lists.llvm.org
Tue Mar 31 10:55:32 PDT 2020

+1 to all that & cc'ing a few of the usual suspects as FYI

On Tue, Mar 31, 2020 at 10:36 AM Pavel Labath via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> On 31/03/2020 18:29, Adrian Prantl via llvm-dev wrote:
> > It's great to see someone interested in improving yaml2obj!
> >
> > As far as I'm concerned, the main problem with yam2obj for DWARF
> testcases is that at the moment, it is both too high-level and too
> low-level at the same time. For writing debug info testcases, yaml2obj at
> the moment does not add anything on top of assembler. If it is only
> providing an alternative syntax, and no other features, it isn't that
> useful. Let me explain what I mean:
> >
> > 1. Too high-level
> >
> > For testing parsers we need to be able to create malformed input, so we
> need to be able to manually tweak offsets and headers where necessary. IIRC
> currently yaml2obj always creates section headers automatically, and can do
> so for only one DWARF version. It would be valuable to support more than
> one version of DWARF, and to support them on a per-section basis (it is not
> uncommon to mix a DWARF 5 .debug_info section with a DWARF 4 line table).
> Also there needs to be a way to optionally manually specify headers
> byte-for-byte, for when we do need this.
> >
> > 2. Too low-level
> >
> > For functionality tests, however, we don't want to hardcode things like
> byte offsets, because it makes it extremely hard to write/modify tests by
> hand. It would be awesome if yaml2obj could automatically generate
> abbreviation sections if the user requests it, if their exact layout isn't
> relevant to the test. Similarly, having to manually adjust object file
> metadata, such as Mach-O section load commands or ELF headers every time
> we're editing a test in a way that changes the size of, e.g., the
> .debug_info section prevents us from using yaml2obj for any kind of
> hand-written tests.
> >
> > The tasks you are describing to add explicit syntax for more DWARF
> constructs are also good and necessary, but addressing one or both of these
> problems would be even more important to increase the usefulness of
> yaml2obj for DWARF testing.
> >
> > -- adrian
> >
> Hello Xing,
> I'd like to echo Adrian here. I currently find the assembly much more
> readable and maintainable that the yaml dwarf representation, and so I
> always write tests that way.
> For me personally, the ability to write/edit syntactically correct dwarf
> easily is much more important than being able to generate "incorrect"
> dwarf -- I'm perfectly happy to continue to write the latter in
> assembly, but there is a lot that could be improved about the experience
> of writing "correct" dwarf. Ideally, I'd have a mode where I can just
> write the logical DIE structure (tags, attributes and their values), and
> the tool would split that into the abbrev/loclist/range/etc. sections.
> regards,
> pavel
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