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  1. JDK
  2. JDK-8346832

runtime/CompressedOops/CompressedCPUSpecificClassSpaceReservation.java fails on RISC-V

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    • Icon: Bug Bug
    • Resolution: Fixed
    • Icon: P4 P4
    • 25
    • 24, 25
    • hotspot
    • b05
    • riscv
    • linux

      This test first expects `tryReserveForUnscaled` and `tryReserveForZeroBased` from the process output. In addition, when test
      without CDS, it also expects `reserve_between (range [0x0000000800000000-0x0000100000000000)` which is not lower than zero-based
      limit. But the process output gives `reserve_between (range [0x0000000100000000-0x0000100000000000)`, which is not expected.

      Previously, we have the code handling this case in CompressedKlassPointers::reserve_address_space_for_compressed_classes.
      But I find that the code is gone after JDK-8305895: Implement JEP 450: Compact Object Headers.

      ```
      diff --git a/src/hotspot/cpu/riscv/compressedKlass_riscv.cpp b/src/hotspot/cpu/riscv/compressedKlass_riscv.cpp
      index cffadb4189b..7c8d6b8f5bb 100644
      --- a/src/hotspot/cpu/riscv/compressedKlass_riscv.cpp
      +++ b/src/hotspot/cpu/riscv/compressedKlass_riscv.cpp
      @@ -56,9 +56,9 @@ char* CompressedKlassPointers::reserve_address_space_for_compressed_classes(size
           result = reserve_address_space_for_zerobased_encoding(size, aslr);
         }

      - // Failing that, optimize for case (3) - a base with only bits set between [33-44)
      + // Failing that, optimize for case (3) - a base with only bits set between [32-44)
         if (result == nullptr) {
      - const uintptr_t from = nth_bit(32 + (optimize_for_zero_base ? LogKlassAlignmentInBytes : 0));
      + const uintptr_t from = nth_bit(32);
           constexpr uintptr_t to = nth_bit(44);
           constexpr size_t alignment = nth_bit(32);
           result = reserve_address_space_X(from, to, size, alignment, aslr);
      ```

      It seems to me more reasonable to add the optimize_for_zero_base check back and replace the LogKlassAlignmentInBytes with
      CompressedKlassPointers::max_shift(). max_shift() is used in CompressedKlassPointers::reserve_address_space_for_zerobased_encoding
      to calculate zerobased_max as well [1].

      Testing: same test passes with fastdebug build on linux-riscv64 platform.

      [1] https://github.com/openjdk/jdk/blob/master/src/hotspot/share/oops/compressedKlass.cpp#L201

            fyang Fei Yang
            fyang Fei Yang
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              Created:
              Updated:
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