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Subject: Re: [PATCH v5 1/2] check-uapi: Introduce check-uapi.sh
From:   Mark Wielaard <mark@klomp.org>
To:     John Moon <quic_johmoo@quicinc.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     Masahiro Yamada <masahiroy@kernel.org>,
        Nathan Chancellor <nathan@kernel.org>,
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        Bjorn Andersson <andersson@kernel.org>,
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        Matthias Maennich <maennich@google.com>,
        Giuliano Procida <gprocida@google.com>,
        kernel-team@android.com, libabigail@sourceware.org,
        Jordan Crouse <jorcrous@amazon.com>,
        Trilok Soni <quic_tsoni@quicinc.com>,
        Satya Durga Srinivasu Prabhala <quic_satyap@quicinc.com>,
        Elliot Berman <quic_eberman@quicinc.com>,
        Guru Das Srinagesh <quic_gurus@quicinc.com>
Date:   Thu, 13 Apr 2023 16:37:14 +0200
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Hi,

On Wed, 2023-04-12 at 09:37 -0700, John Moon via Libabigail wrote:
> On 4/11/2023 11:14 PM, Greg Kroah-Hartman wrote:
> > > Would you find the tool more useful if it simply filtered out all instances
> > > where the size of the type did not change? This would filter out the
> > > following which the tool currently flags:
> > > 
> > > - enum expansions
> > > - reserved field expansions
> > > - expansions of a struct with a flex array at the end
> > > - type changes
> > > - re-ordering of existing members
> > > - ...others?
> > 
> > Obviously not, as some of those are real breakages, and some are not at
> > all.
> > 
> > Please understand what is an abi breakage.  Adding new enums is not.
> > Using a reserved field is not.  Reording existing members IS.
> > 
> 
> Yes, understood that method would miss certain classes of breakages. I 
> was suggesting it as a way to improve the signal-to-noise ratio of the 
> tool since we don't currently have an algorithm for determining 
> breakages with 100% accuracy.

Note that you can check the exit code of libabigail's abidiff to see
whether something is an incompatible abi change or not, see:
https://sourceware.org/libabigail/manual/abidiff.html#return-values

You can also of course use suppressions to instruct abidiff to avoid
reporting changes involving certain ABI artifacts:
https://sourceware.org/libabigail/manual/libabigail-concepts.html#suppr-spec-label

Cheers,

Mark