linux-kernel - Re: [PATCH v2 0/2] Validating UAPI backwards compatibility

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Date:   Wed, 1 Mar 2023 09:50:30 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     John Moon <quic_johmoo@...cinc.com>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nicolas Schier <nicolas@...sle.eu>,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Arnd Bergmann <arnd@...db.de>,
        Bjorn Andersson <andersson@...nel.org>,
        Todd Kjos <tkjos@...gle.com>,
        Matthias Maennich <maennich@...gle.com>,
        Giuliano Procida <gprocida@...gle.com>,
        kernel-team@...roid.com, libabigail@...rceware.org,
        Jordan Crouse <jorcrous@...zon.com>,
        Trilok Soni <quic_tsoni@...cinc.com>,
        Satya Durga Srinivasu Prabhala <quic_satyap@...cinc.com>,
        Elliot Berman <quic_eberman@...cinc.com>
Subject: Re: [PATCH v2 0/2] Validating UAPI backwards compatibility

On Tue, Feb 28, 2023 at 11:54 PM John Moon <quic_johmoo@...cinc.com> wrote:
>
> Currently, the script works with gcc. It generates output like this when
> a backwards-incompatible change is made to a UAPI header:
>
>  !!! ABI differences detected in include/uapi/linux/acct.h (compared to
>  file at HEAD^1) !!!
>
>      [C] 'struct acct' changed:
>        type size changed from 512 to 544 (in bits)
>        1 data member insertion:
>          '__u32 new_val', at offset 512 (in bits) at acct.h:71:1
>
>  0/1 UAPI header file changes are backwards compatible
>  UAPI header ABI check failed
>
> However, we have not had success with clang. It seems clang is more
> aggressive in optimizing dead code away (no matter which options we
> pass). Therefore, no ABI differences are found.

Hi John,
Do you have the list of bugs you've filed upstream against clang wrt.
information missing when using `-fno-eliminate-unused-debug-types`?

https://github.com/llvm/llvm-project/issues is the issue tracker.

Seeing a strong participant in both the Android and LLVM ecosystems
supply scripts that lack clang support...raises eyebrows.
-- 
Thanks,
~Nick Desaulniers