[Dwarf-Discuss] line table dir/file

[Eric Christopher]

Hi Paul,

I too remember this discussion and clang's implementation is how I saw this
being added when we did.

-eric

On Mon, Feb 24, 2020 at 11:34 AM Robinson, Paul via Dwarf-Discuss <
dwarf-discuss at lists.dwarfstd.org> wrote:

> Hmmm.
>
> When the committee was reworking the file/dir tables for DWARF v5,
> one thing that came up was that the root file/directory were *not*
> in the .debug_line section, and therefore the line table could not
> be interpreted fully without a .debug_info section, because that
> was where the root file and compilation directory were kept--not
> in the line table itself.  Am I imagining this discussion?  We
> added text to the document specifically describing file/dir 0 and
> that they were to be explicitly kept (duplicated from .debug_info)
> so that the .debug_line section could be fully dumped even in the
> absence of a corresponding .debug_info section.  This was the
> "strip all but the line table" scenario.
>
> I can easily believe that nobody *actually uses* file/dir 0, but
> that's a different question from what producers are supposed to
> produce in v5 and how consumers are supposed to interpret it.
>
> Offhand it looks like there are three possibilities:
> a) Clang got it right and everyone else got it wrong.
> b) The spec is ambiguous and we're observing the consequences.
> c) Clang got it wrong and everyone else got it right.
>
> But in all three cases, we need to settle on (i) what the spec
> actually says, (ii) does it say what the committee intended,
> (iii) if not, what to do about it.
>
> I don't think we should start with (iii).
> --paulr
>
> > -----Original Message-----
> > From: Dwarf-Discuss <dwarf-discuss-bounces at lists.dwarfstd.org> On Behalf
> > Of David Anderson via Dwarf-Discuss
> > Sent: Friday, February 21, 2020 5:40 PM
> > To: dwarf-discuss at lists.dwarfstd.org
> > Subject: [Dwarf-Discuss] line table dir/file
> >
> > I've attached a pdf that
> > shows some cases of current usage of the line
> > table directory and file arrays and of indexes.
> >
> > clang seems (with my limited access to other compilers)
> > the outlier in treating a index of 0 (from file [N] to
> > the directory)  as
> > a 0 origin references.
> > Only 0-origin for DWARF5.
> >
> > So reserving 0 as an index to the directories table
> > to mean 'no directory available'  would
> > seem to be the right course.
> >
> > The standard (or an errata, if we do such a thing)
> > needs works to establish 1-origin for these indexes into
> > the directory table and clarifies the 1-origin
> > indexes by referencing such in more places
> > in the document.
> >
> > A tar.gz of the test setup is available by email
> > if anyone cares.  It is about 1 MiB in size (most
> > of the size is in two ancient IRIX Elf files)..
> >
> > David Anderson
> >
>
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