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

mark at klomp dot org sourceware-bugzilla@sourceware.org
Sat Sep 11 23:43:13 GMT 2021


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

--- Comment #2 from Mark Wielaard <mark at klomp dot org> ---
(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_type        abbrev: 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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