[Bug libdw/30967] Discriminator in Dwarf_Line_s may exceed 24 bits

["mark at klomp dot org" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=30967

Mark Wielaard <mark at klomp dot org> changed:

           What    |Removed                     |Added
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                 CC|                            |roland at gnu dot org

--- Comment #5 from Mark Wielaard <mark at klomp dot org> ---
(In reply to Aleksei Vetrov from comment #4)
> (In reply to Frank Ch. Eigler from comment #3)
> > Is there some reason not to just bump up that bitfield width from :24 to :32
> > or more for now, until a deeper analysis of llvm informs us as to how wide
> > these discriminator codes can really be?
> 
> For me it is ok to bump that bitfield, but there is a warning in the code:
> 
> > All the flags and other bit fields should add up to 48 bits
> > to give the whole struct a nice round size.
> 
> So this question should be directed to the author of this code: Roland
> McGrath <roland@redhat.com>. I think there may be slight performance/memory
> issues, but as a temporary solution it looks good.

Added Roland (now with another email address) to the CC.

Note that we have blown the size of this struct already to support the NVIDIA
extensions :{

The issue here is that we create (very) large arrays of struct Dwarf_Line_s and
we do that eagerly, see bug #27405

So we would like to keep that struct as small as possible.

Another "solution"/workaround would be to just ignore such crazy big
discriminator values and just set them to zero or store them modulo 24 bits
(they are probably still unique then).

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