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From: "gprocida+abigail at google dot com" <sourceware-bugzilla@sourceware.org>
To: libabigail@sourceware.org
Subject: [Bug default/26807] New: Issues with enum-underlying types
Date: Thu, 29 Oct 2020 10:08:11 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D26807

            Bug ID: 26807
           Summary: Issues with enum-underlying types
           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.

I've posted an RFC patch which illustrates a few issues with libabigail's
treatment of enum-underlying types.

https://sourceware.org/pipermail/libabigail/2020q4/002788.html

Repeating them here:

- signedness and changes thereof (as seen in DWARF) are not modelled
- size and alignment changes are reported twice
- size changes are not considered ABI incompatibilities
- *all* enum-underlying types are currently considered anonymous
  and have the same name, even when they differ in size, alignment or
  signedness=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20

The last item is closely related to the others but is troublesome in a
different way. It can cause non-deterministic ordering of such types in XML
output (in the presence of concurrent heap-allocation by other threads). In
particular, it causes test flakiness.

I've not attempted to find a way that signedness changes can cause API
surprises. However, there are mentions of undefined behaviour that may occur
when casting in https://en.cppreference.com/w/cpp/language/enum.

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