[PATCH] Add a UnitKind field to DWARFUnit so that we can discriminate the unit's origin section.

[David Blaikie]

On Wed, Sep 10, 2014 at 12:45 AM, Frédéric Riss <friss at apple.com> wrote:

>
> > On 09 Sep 2014, at 23:40, David Blaikie <dblaikie at gmail.com> wrote:
> >
> >
> >
> > On Tue, Sep 9, 2014 at 5:53 AM, Frederic Riss <friss at apple.com> wrote:
> > Hi dblaikie, samsonov, echristo, aprantl,
> >
> > There is no simple way to get the origin section of a DWARFUnit. It is
> necessary
> > to know from which section a Unit has been extracted to be able to
> resolve
> > cross-unit references (to find the right list to search fo the reference
> > target).
> >
> > Would it make more sense to give it the actual section (or some kind of
> alias/handle to it) rather than a flag? That way it'd work for fission
> (split-dwarf) as well, and type units that may be in comdat sections?
>
> Although this discriminates on origin section, the way it’s used is just
> to lookup the right Unit list in the context.


OK - then perhaps it should just be a pointer/reference/whatever to the
relevant unit list? Or do you need this for other purposes as well?


> It’s not the actual section that matters (the unit already contains a
> StringRef pointing to the section data). The next patch introduces:
>
> DWARFUnit *DWARFContext::getUnitForOffset(const DWARFUnit *Unit, uint32_t
> Offset) {
>    switch (Unit->getKind()) {
>    case DWARFUnit::UK_Compile:
>      return getCompileUnitForOffset(Offset);
>    case DWARFUnit::UK_DWOCompile:
>      return getDWOCompileUnitForOffset(Offset);
>    case DWARFUnit::UK_Type:
>      return getTypeUnitForOffset(Offset);
>    case DWARFUnit::UK_DWOType:
>      return getDWOTypeUnitForOffset(Offset);
>    }
>    llvm_unreachable("Unkown unit type in getUnitForOffset.");
>  }
>
> I’m open to any other way to achieve that. And this handles LTO and
> fission uses (or I can’t see what issues you’re thinking about).
>
> Fred
>
> >
> > This patch adds a field and an accessor to the DWARFUnit that indicates
> where
> > it originated from. This information will be used in a subsequent patch
> to
> > implement a generic version of
> DWARFContext::getCompilationUnitForOffset()
> > that will work with arbitrary unit types.
> >
> > Note that this is nearly implemented like the start of LLVM-style RTTI
> for
> > the DWARFUnit, but it seems that we don't need separate classes to
> represent
> > the DWO variants of Units as only their origin changes. Thus we only
> > introduce this discriminant field.
> >
> > http://reviews.llvm.org/D5264
> >
> > Files:
> >   lib/DebugInfo/DWARFCompileUnit.h
> >   lib/DebugInfo/DWARFContext.cpp
> >   lib/DebugInfo/DWARFTypeUnit.h
> >   lib/DebugInfo/DWARFUnit.cpp
> >   lib/DebugInfo/DWARFUnit.h
> >
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20140910/48691ee0/attachment.html>