[PATCH] D30357: [ObjectYAML] NFC. Refactor DWARFYAML CompileUnit dump code

[Chris Bieneman via Phabricator via llvm-commits]

beanz added inline comments.


================
Comment at: lib/ObjectYAML/DWARFVisitor.cpp:59
+              writeSize =
+                  DebugInfo.DebugLines[0].TotalLength == UINT32_MAX ? 8 : 4;
+            OnVariableSizeValue(FormVal->Value, writeSize);
----------------
probinson wrote:
> beanz wrote:
> > aprantl wrote:
> > > This would be easier to read if written like this:
> > > ```
> > > uint64_t?? writeSize;
> > > if (!DebugInfo.DebugLines.empty())
> > >   writeSize =  DebugInfo.DebugLines[0].TotalLength == UINT32_MAX ? 8 : 4;
> > > else if (Unit.Version == 2)
> > >   writeSize = Unit.AddrSize
> > > else
> > >   writeSize = 4;
> > > ```
> > There is actually some slightly incorrect logic here. The correct logic should be more like:
> > 
> > 
> > ```
> > size_t writeSize = 4;
> > if (Unit.Version == 2)
> >   writeSize = Unit.AddrSize;
> > else if (!DebugInfo.DebugLines.empty())
> >   writeSize = DebugInfo.DebugLines[0].TotalLength == UINT32_MAX ? 8 : 4;
> > ```
> > 
> > The idea being that size 4 as a default is sane. If version == 2, then you use AddrSize, otherwise it is based on whether it is DWARF32 or DWARF64 which requires the Line table.
> Why do you need the line table?  Every unit has a length that lets you determine its 32/64 format.
Reading the DWARF 4 spec (7.2.2 Initial Length Values) I believe you are correct that the unit's should start with a length that lets you determine the 32/64 format, however I don't believe that is how our parser is written:

https://github.com/llvm-mirror/llvm/blob/master/lib/DebugInfo/DWARF/DWARFUnit.cpp#L91

It looks to me like we only ever read a 32-bit value for the length from the unit.

Am I misunderstanding something here?


https://reviews.llvm.org/D30357