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From: "gprocida+abigail at google dot com" <sourceware-bugzilla@sourceware.org>
To: libabigail@sourceware.org
Subject: [Bug default/26297] New: Possible misinterpretation of
 DW_AT_declaration via DW_AT_specification
Date: Thu, 23 Jul 2020 18:27:00 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D26297

            Bug ID: 26297
           Summary: Possible misinterpretation of DW_AT_declaration via
                    DW_AT_specification
           Product: libabigail
           Version: unspecified
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: default
          Assignee: dodji at redhat dot com
          Reporter: gprocida+abigail at google dot com
                CC: libabigail at sourceware dot org
  Target Milestone: ---

Hi Dodji.

I was looking into libabigail's emission of anonymous declaration-only unio=
ns
and starting comparing what I saw there against what dwarfdump and pahole -=
aAE
reported. The pahole output didn't look entirely trustworthy.

dwarfdump tests/data/test-read-dwarf/libtest23.so

shows a DW_TAG_union with a DW_AT_declaration yes attribute. I thought "how=
's
that?" but spotted that it was referred to via a DW_AT_specification attrib=
ute
from another declaration.

A little web search found the discussion

https://gdb-patches.sourceware.narkive.com/PLB1ixbx/dw-at-specification-lon=
g-ago-gdb-change

which concluded that DW_AT_declaration found by following a DW_AT_specifica=
tion
should be ignored.

I coded a naive change that plumbed through a "followed_spec" boolean throu=
gh
bits of the DWARF reader and the results were quite startling.

Please take a look at this and let me know your thoughts.

https://github.com/myxoid/libabigail/commit/fb3b7302a9923b8ee7ca279cc949220=
7140d886d

It may be useful to switch some tests to --type-id-style hash and turn on
annotation to better understand the changes.=20

Regards,
Giuliano.

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