RFR: JDK-8313790: [arm32] Specify -marm when building without an ABI profile [v2]

[Magnus Ihse Bursie]

On Sat, 4 Nov 2023 06:39:34 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

>> See [JDK-8288719](https://bugs.openjdk.org/browse/JDK-8288719) and subsequent [discussion](https://mail.openjdk.org/pipermail/build-dev/2022-May/034635.html) back in 2022.
>> 
>> On Arm, we can generate either arm- or thumb-code (`-marm` or `-mthumb`). 
>> 
>> At the moment, if we don't specify an ABI profile (`--with_abi_profile`) when configuring the build, we call gcc without `-marm` or `-mthumb`. Then we use whatever the toolchain defaults too, which is pretty much random (it depends on how the toolchain itself had been built). That can cause really rare but tricky problems when combining static assembly and C++ code (See e.g. JDK-8288719).
>> 
>> I propose to always specify `-marm` as default, unless an ABI profile is given, to prevent such errors.
>> 
>> Thanks to @marchof for testing this.
>
> Thomas Stuefe has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains eight additional commits since the last revision:
> 
>  - Merge branch 'openjdk:master' into JDK-8313790-arm32-Specify-marm-when-building-without-an-ABI-profile
>  - Merge branch 'openjdk:master' into JDK-8313790-arm32-Specify-marm-when-building-without-an-ABI-profile
>  - Merge branch 'openjdk:master' into JDK-8313790-arm32-Specify-marm-when-building-without-an-ABI-profile
>  - Merge branch 'openjdk:master' into JDK-8313790-arm32-Specify-marm-when-building-without-an-ABI-profile
>  - Merge branch 'openjdk:master' into JDK-8313790-arm32-Specify-marm-when-building-without-an-ABI-profile
>  - Merge branch 'openjdk:master' into JDK-8313790-arm32-Specify-marm-when-building-without-an-ABI-profile
>  - Merge branch 'openjdk:master' into JDK-8313790-arm32-Specify-marm-when-building-without-an-ABI-profile
>  - start

I thought `--with-abi-profile` was required when building on arm32. Would that not be a better fix to do?

(And even if we don't go that route, I think it would be better to have an "else" clause that sets the fallback value you propose here, rather than to set it once at the start and then overwrite it for almost all cases.)

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PR Comment: https://git.openjdk.org/jdk/pull/15162#issuecomment-1794703170
PR Comment: https://git.openjdk.org/jdk/pull/15162#issuecomment-1794705921