RFR: 8366777: Build fails unknown pseudo-op with old AS on linux-aarch64 [v13]

[Erik Joelsson]

On Thu, 11 Sep 2025 14:11:39 GMT, SendaoYan <syan at openjdk.org> wrote:

>> Hi all,
>> 
>> Build jdk on linux-aarch64 with older assembler version(as 2.30) will report compilation failre, shows as [JDK-8366777](https://bugs.openjdk.org/browse/JDK-8366777).
>> 
>> This PR add the expression `svfloat64_t a() {}` to makefile which will trigger the compilation during configure stage. After this PR, at configure stage will check the gcc and assember support `-march=armv8-a+sve` or not more comprehensive.
>> 
>> Testing:
>> - [x] On linux-aarch64 gcc12.3.1 as2.37, configure set SVE_CFLAGS as '-march=armv8-a+sve'
>> - [x] On linux-aarch64 gcc10.3.0 as2.30, configure set SVE_CFLAGS as empty
>> 
>> 
>> The compilation fails demo as below:
>> 
>> 
>> # cat sve.c 
>> #include <arm_sve.h>
>> svfloat64_t a() {}
>> # gcc -march=armv8-a+sve sve.c 
>> /tmp/ccVOzMzb.s: Assembler messages:
>> /tmp/ccVOzMzb.s:6: Error: unknown pseudo-op: `.variant_pcs'
>
> SendaoYan has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Create a seperate macro FLAGS_SETUP_SVE

This definitely looks better but still some things that can be improved.

make/autoconf/flags-other.m4 line 116:

> 114:   UTIL_ARG_ENABLE(NAME: aarch64-sve, DEFAULT: auto,
> 115:     RESULT: AARCH64_SVE_ENABLED,
> 116:     DESC: [Use SVE when compile libsleef],

Suggestion:

    DESC: [Use SVE when compiling libsleef],

make/autoconf/flags-other.m4 line 119:

> 117:     CHECK_AVAILABLE: [
> 118:       # Check whether the compiler supports the Arm C Language Extensions (ACLE)
> 119:       # for SVE. Set SVE_CFLAGS to -march=armv8-a+sve if it does.

This comment is a bit out of date with the code now. This is just the check available part. Maybe move this to before the macro call?

make/autoconf/flags-other.m4 line 140:

> 138:           ])],
> 139:           [AVAILABLE=yes],
> 140:           [AVAILABLE=no]

The documentation of `UTIL_ARG_ENABLE` says that `AVAILABLE` needs to be set to `false` when not available.

make/autoconf/flags-other.m4 line 146:

> 144:         CFLAGS="$saved_cflags"
> 145:         AC_LANG_POP([C])
> 146:       fi

I think we need `AVAILABLE=fallse` when not matching the toolchain. This can also be expressed as `AVAILABLE: false` as a parameter to `UTIL_ARG_ENABLE`. The `CHECK_AVAILABLE` gets a chance to overwrite that value.

make/autoconf/flags-other.m4 line 167:

> 165:     fi
> 166:     CFLAGS="$OLD_CFLAGS"
> 167:     AC_LANG_POP(C)

This part should be included in the `IF_ENABLED` block in `UTIL_ARG_ENABLE`.

-------------

PR Review: https://git.openjdk.org/jdk/pull/27073#pullrequestreview-3213638099
PR Review Comment: https://git.openjdk.org/jdk/pull/27073#discussion_r2342338970
PR Review Comment: https://git.openjdk.org/jdk/pull/27073#discussion_r2342341790
PR Review Comment: https://git.openjdk.org/jdk/pull/27073#discussion_r2342355196
PR Review Comment: https://git.openjdk.org/jdk/pull/27073#discussion_r2342354523
PR Review Comment: https://git.openjdk.org/jdk/pull/27073#discussion_r2342359541