On Fri, 20 May 2022 08:36:28 GMT, Magnus Ihse Bursie <i...@openjdk.org> wrote:
>> On AArch64 it is sometimes convenient to have LSE atomics right from the >> start. Currently they are enabled after feature detection and RR reverse >> debugger works incorrectly. >> >> New build configuration feature 'hardlse' is added. If it is enabled for >> aarch64 type of build, then statically compiled stubs replace the initial >> pessimistic implementation and dynamically generated replacements (when LSE >> support is detected). The feature works for builds of all debug levels. >> >> New file atomic_linux_aarch64_lse.S is derived from atomic_linux_aarch64.S >> and inherits its copyright. This alternative static implementation >> corresponds to the dynamically generated code. >> >> Note, this configuration part is necessary but not sufficient to fully avoid >> strex instructions for practical purposes. Other parts are: >> >> * Run on the OS built without strex family instructions. E.g. Amazon Linux >> 2022. >> * Compile with outline atomics enabled and the configuration flag enabled. >> E.g. configure with >> --with-extra-cflags='-march=armv8.3-a+crc+crypto -moutline-atomics' >> --with-extra-cxxflags='-march=armv8.3-a+crc+crypto -moutline-atomics' >> --with-extra-ldflags='-Wl,--allow-multiple-definition' >> --with-jvm-features=hardlse >> >> Testing: tier1, tier2 on linux-aarch64 release builds with feature off and >> feature on. > > make/autoconf/jvm-features.m4 line 442: > >> 440: JVM_FEATURES_VARIANT_FILTER="link-time-opt opt-size" >> 441: fi >> 442: # Filter out hardlse feature by default > > You should not set up a PLATFORM filter in `JVM_FEATURES_PREPARE_VARIANT`. > > In fact, you will need a `JVM_FEATURES_CHECK_HARD_LSE`, which verifies that > it can only be enabled on aarch64. See e.g. `JVM_FEATURES_CHECK_JVMCI` foor > inspiration on how to write this and where to call it. I suggest you set up > `JVM_FEATURES_PLATFORM_FILTER` in that function as well. Magnus, thank you for the comments. I'm taking a direction suggested by Andrew and Nick -- linux-aarch64 only solution without build configuration feature, determined by actual compiler flags. Will update the PR shortly after some final testing. ------------- PR: https://git.openjdk.java.net/jdk/pull/8779
