On Wed, 18 Oct 2023 04:44:26 GMT, Jorn Vernee <jver...@openjdk.org> wrote:
>> Add the ability to pass heap segments to native code. This requires using >> `Linker.Option.critical(true)` as a linker option. It has the same >> limitations as normal critical calls, namely: upcalls into Java are not >> allowed, and the native function should return relatively quickly. Heap >> segments are exposed to native code through temporary native addresses that >> are valid for the duration of the native call. >> >> The motivation for this is supporting existing Java array-based APIs that >> might have to pass multi-megabyte size arrays to native code, and are >> current relying on Get-/ReleasePrimitiveArrayCritical from JNI. Where making >> a copy of the array would be overly prohibitive. >> >> Components of this patch: >> >> - New binding operator `SegmentBase`, which gets the base object of a >> `MemorySegment`. >> - Rename `UnboxAddress` to `SegmentOffset`. Add flag to specify whether >> processing heap segments should be allowed. >> - `CallArranger` impls use new binding operators when >> `Linker.Option.critical(/* allowHeap= */ true)` is specified. >> - `NativeMethodHandle`/`NativeEntryPoint` allow `Object` in their signatures. >> - The object/oop + offset is exposed as temporary address to native code. >> - Since we stay in the `_thread_in_Java` state, we can safely expose the >> oops passed to the downcall stub to native code, without needing GCLocker. >> These oops are valid until we poll for safepoint, which we never do >> (invoking pure native code). >> - Only x64 and AArch64 for now. >> - I've refactored `ArgumentShuffle` in the C++ code to no longer rely on >> callbacks to get the set of source and destination registers (using >> `CallingConventionClosure`), but instead just rely on 2 equal size arrays >> with source and destination registers. This allows filtering the input java >> registers before passing them to `ArgumentShuffle`, which is required to >> filter out registers holding segment offsets. Replacing placeholder >> registers is also done as a separate pre-processing step now. See changes >> in: >> https://github.com/openjdk/jdk/pull/16201/commits/d2b40f1117d63cc6d74e377bf88cdcf6d15ff866 >> - I've factored out `DowncallStubGenerator` in the x64 and AArch64 code to >> use a common `DowncallLinker::StubGenerator`. >> - Fallback linker is also supported using JNI's >> `GetPrimitiveArrayCritical`/`ReleasePrimitiveArrayCritical` >> >> Aside: fixed existing issue with `DowncallLinker` not properly acquiring >> segments in interpreted mode. >> >> Numbers for the included benchmark on my machine are: >> >> >> Benchmar... > > Jorn Vernee has updated the pull request incrementally with one additional > commit since the last revision: > > drop unused in_reg_spiller src/java.base/share/classes/jdk/internal/foreign/abi/aarch64/CallArranger.java line 156: > 154: > 155: BindingCalculator argCalc = forUpcall ? new > BoxBindingCalculator(true) : new UnboxBindingCalculator(true, > forVariadicFunction, options.allowsHeapAccess()); > 156: BindingCalculator retCalc = forUpcall ? new > UnboxBindingCalculator(false, forVariadicFunction, false) : new > BoxBindingCalculator(false); asymmetry noted - that said, not much that can be done here - as for an upcall it is not clear what the surrounding context is (e.g. where's the place where unpinning happens) src/java.base/share/classes/jdk/internal/foreign/abi/fallback/FallbackLinker.java line 188: > 186: acquiredSessions.add(sessionImpl); > 187: if (invData.allowsHeapAccess() && !ms.isNative()) { > 188: heapBases[i] = ms.heapBase().get(); This will fail if the segment is read-only. Use the unsafe variant. ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/16201#discussion_r1363562390 PR Review Comment: https://git.openjdk.org/jdk/pull/16201#discussion_r1363566076
