[Bug libdw/28294] dwarf_aggregate_size fails on some array types

[mark at klomp dot org via Elfutils-devel]

https://sourceware.org/bugzilla/show_bug.cgi?id=28294

Mark Wielaard  changed:

   What|Removed |Added

 Status|UNCONFIRMED |ASSIGNED
 CC||mark at klomp dot org
   Last reconfirmed||2021-09-11
 Ever confirmed|0   |1
   Assignee|unassigned at sourceware dot org   |mark at klomp dot org

--- Comment #1 from Mark Wielaard  ---
Created attachment 13662
  --> https://sourceware.org/bugzilla/attachment.cgi?id=13662&action=edit
Use type of subrange (if any) to determine signedness of upper/lower values

Check if the subrange has an associate type, if it does then check the type to
determine whether the upper and lower values need to be interpreted as signed
of unsigned values. We default to signed because that is what
run-aggregate-size.sh testfile-size4 expects (but it is an hardwritten
testcase, we can flip the default if that makes more sense).

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[Bug libdw/28294] dwarf_aggregate_size fails on some array types

[mark at klomp dot org via Elfutils-devel]

https://sourceware.org/bugzilla/show_bug.cgi?id=28294

--- Comment #2 from Mark Wielaard  ---
(In reply to Eli Boling from comment #0)
> In dwarf_aggregate_size.c, the helper function array_size unconditionally
> uses dwarf_formsdata to obtain the value of the DW_AT_upper_bound attribute
> for array types.  In many cases, this will return a negative value for C
> arrays that have positive upper bounds, causing the function to return a
> failure value, which propagates up through dwarf_aggregate_size.
> 
> This is an exemplary type (via readelf -w):
>  <1><90e>: Abbrev Number: 37 (DW_TAG_array_type)
> <90f>   DW_AT_type: <0x118>
>  <2><913>: Abbrev Number: 11 (DW_TAG_subrange_type)
> <914>   DW_AT_type: <0x2c>
> <918>   DW_AT_upper_bound : 249
> 
> And the same type, via eu-readelf --debug-dump=info:
>  [   90e]array_type   abbrev: 37
>  type (ref4) [   118]
>  [   913]  subrange_typeabbrev: 11
>type (ref4) [2c]
>upper_bound  (data1) 249
> 
> If dwarf_aggregate_size is called on this type, when it gets the upper_bound
> attribute, it will get a value of -7, and fail.  For other array sizes, this
> will work.
> 
> Looking around a bit, the closest discussion I could find on the topic was
> this one about signed vs unsigned interpretation of array bounds back in
> 2005:
> http://www.dwarfstd.org/ShowIssue.php?issue=020702.1
> 
> I exchanged emails with Mark Wielaard on this, and he indicated that this
> did appear to be a bug, but he wasn't sure yet where the correct fix would
> be.

Could you try the attached patch?
I don't know if it works, it depends on the subrange_type at [2c].
If it doesn't work, could you post the full debug-dump or attach a test binary?

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