`-ftrivial-auto-var-init=pattern` [1] supported by gcc-12 was added recently to help detect uses of uninitialized memory. [2] Under this extension mode, `__builtin_clear_padding` is called to clear the padding bits in object representation. But the builtin function does not support variable length aggregates [3].
`vfloat2_sve_sleef` is a typedef of `svfloat32x2_t`, which is defined as an opaque sizeless type in ARM C Language Extensions (ACLE) [4]. When `__builtin_clear_padding` is applied to such a type, it triggers the unsupported code path and results in build failures when compiling libsleef on Linux-AArch64, as reported in JDK-8364185 [5]. Switching the initialization mode with gcc-12 from `pattern` to `zero` avoids the use of this unsupported `__builtin_clear_padding` and resolves the issue. I did not encounter similar problems when building with Clang-16 [6]. This patch changes the initialization mode from `pattern` to `zero` when compiling libsleef SVE component on Linux-AArch64 with gcc-12 to fix the build failure and help avoid potential security issues related to uninitialized padding Testing (combined with https://github.com/openjdk/jdk/pull/26577): 1. Release and fastdebug build with gcc-11, gcc-12, and clang-16 2. `test/jdk/jdk/incubator/vector` passed on both 256-bit SVE and NEON machines [1] https://gcc.gnu.org/onlinedocs/gcc-12.1.0/gcc/Optimize-Options.html#index-ftrivial-auto-var-init [2] https://github.com/openjdk/jdk/commit/fae37aaae8b36fd74309b84fa1fdf017c7d932ed [3] https://gcc.gnu.org/pipermail/gcc-patches/2020-November/559214.html [4] https://arm-software.github.io/acle/main/acle.html#arm_sveh [5] https://bugs.openjdk.org/browse/JDK-8364185 [6] https://releases.llvm.org/16.0.0/tools/clang/docs/ReleaseNotes.html ------------- Commit messages: - 8365312: __builtin_clear_padding not supported for variable length aggregates Changes: https://git.openjdk.org/jdk/pull/26755/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26755&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8365312 Stats: 11 lines in 1 file changed: 11 ins; 0 del; 0 mod Patch: https://git.openjdk.org/jdk/pull/26755.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/26755/head:pull/26755 PR: https://git.openjdk.org/jdk/pull/26755
