Re: [Linaro-TCWG-CI] gcc-16-7434-g6b550d69fe7c: 2 regressions on master-thumb_m55_hard_eabi

I think this is the same issue as reported in
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124124,
that was addressed by:

commit r16-7911-g3a41229f92022bfb388911854d597721fce76714
<https://gcc.gnu.org/cgit/gcc/commit/?id=3a41229f92022bfb388911854d597721fce76714>
Author: Tomasz KamiÅski <[email protected]>
Date:   Thu Mar 5 08:57:24 2026 +0100

    libstdc++: Fix atomic/cons/zero_padding.cc test for arm-none-eabi
[PR124124 <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124124>]

    The test uses dg-require-atomic-cmpxchg-word that checks if atomic compare
    exchange is available for pointer sized integers, and then test types that
    are eight bytes in size. This causes issue for targets for which pointers
    are four byte and libatomic is not present, like arm-none-eabi.

    This patch addresses by using short member in TailPadding and MidPadding,
    instead of int. This reduces the size of types to four bytes, while keeping
    padding bytes present.

            PR libstdc++/124124
<https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124124>

    libstdc++-v3/ChangeLog:

            * testsuite/29_atomics/atomic/cons/zero_padding.cc: Limit size of
            test types to four bytes.



On Sun, Mar 22, 2026 at 9:01 PM <[email protected]> wrote:

> Dear contributor,
>
> Our automatic CI has detected problems related to your patch(es). Please
> find some details below.
>
> In  arm-eabi cortex-m55 hard, after:
>   | commit gcc-16-7434-g6b550d69fe7c
>   | Author: Tomasz Kamiński <[email protected]>
>   | Date:   Thu Jan 29 18:14:47 2026 +0100
>   |
>   |     libstdc++: Allow constant initialization of std::atomic of types
> with padding [PR123875]
>   |
>   |     Currently for the types T that contains padding bits,
> std::atomic<T>(T)
>   |     constructor was not usable at compile-time in C++14 or later
> modes. This
>   |     regression caused by use of __builtin_clear_padding introduced in
>   | ... 49 lines of the commit log omitted.
>
> Produces 2 regressions:
>   |
>   | regressions.sum:
>   | Running libstdc++:libstdc++-dg/conformance.exp ...
>   | FAIL: 29_atomics/atomic/cons/static_zero_padding.cc -std=gnu++20 (test
> for excess errors)
>   | UNRESOLVED: 29_atomics/atomic/cons/static_zero_padding.cc -std=gnu++20
> compilation failed to produce executable
>
> Used configuration :
>  *CI config* tcwg_gnu_embed_check_gcc arm-eabi -mthumb
> -march=armv8.1-m.main+mve.fp+fp.dp -mtune=cortex-m55 -mfloat-abi=hard
> -mfpu=auto
>  *configure and test flags:* --target arm-eabi --disable-multilib
> --with-mode=thumb --with-arch=armv8.1-m.main+mve.fp+fp.dp --with-float=hard
> --target_board=-mthumb/-march=armv8.1-m.main+mve.fp+fp.dp/-mtune=cortex-m55/-mfloat-abi=hard/-mfpu=auto
> qemu-cpu=cortex-m55
>
> We track this bug report under
> https://linaro.atlassian.net/browse/GNU-1865. Please let us know if you
> have a fix.
>
> If you have any questions regarding this report, please ask on
> [email protected] mailing list.
>
>
> -----------------8<--------------------------8<--------------------------8<--------------------------
>
> The information below contains the details of the failures, and the ways
> to reproduce a debug environment:
>
> You can find the failure logs in *.log.1.xz files in
>  *
> https://ci.linaro.org/job/tcwg_gnu_embed_check_gcc--master-thumb_m55_hard_eabi-build/1098/artifact/artifacts/00-sumfiles/
> The full lists of regressions and improvements as well as configure and
> make commands are in
>  *
> https://ci.linaro.org/job/tcwg_gnu_embed_check_gcc--master-thumb_m55_hard_eabi-build/1098/artifact/artifacts/notify/
> The list of [ignored] baseline and flaky failures are in
>  *
> https://ci.linaro.org/job/tcwg_gnu_embed_check_gcc--master-thumb_m55_hard_eabi-build/1098/artifact/artifacts/sumfiles/xfails.xfail
>
> Current build   :
> https://ci.linaro.org/job/tcwg_gnu_embed_check_gcc--master-thumb_m55_hard_eabi-build/1098/artifact/artifacts
> Reference build :
> https://ci.linaro.org/job/tcwg_gnu_embed_check_gcc--master-thumb_m55_hard_eabi-build/1097/artifact/artifacts
>
> Instruction to reproduce the build :
> https://gitlab.com/LinaroLtd/tcwg/ci/interesting-commits/-/raw/master/gcc/sha1/6b550d69fe7cb62ea6e240ce7a4ba29ce33aa1b1/tcwg_gnu_embed_check_gcc/master-thumb_m55_hard_eabi/reproduction_instructions.txt
>
> Full commit : See in git+ssh://[email protected]/git/gcc.git