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  1. JDK
  2. JDK-8255628

AOT code fails with mismatched UseEmptySlotsInSupers

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      The AOT library must be built with the same UseEmptySlotsInSupers value as used at runtime, since AOT assumes that all field offsets are the same as at runtime. When a mismatched UseEmptySlotsInSupers is specified, AOT code can fail.

      Here's a simple reproducer that fails with a fastdebug build from a recent openjdk repo:

      ==========================================================================================
      # doit.sh
      # Please edit the following two lines
      export JAVA_HOME=/jdk/bld/fastdebug/images/jdk
      export DEVKIT=/home/iklam/devkit/latest

      # Gather the list of classes to compile
      ${JAVA_HOME}/bin/java -Xshare:off -verbose -version 2> /dev/null | grep class.load.*jrt..java.base \
          | sed -e 's/.*class,load..//g' -e 's/ source.*//g' > classes.txt

      # This takes about 160 seconds on a fast machine
      if test ! -f test.so; then
          time ${JAVA_HOME}/bin/jaotc \
              --info \
              -J-Xmx4g \
              -J-server \
              -J-ea \
              -J-esa \
              --compile-commands open/test/hotspot/jtreg/compiler/aot/scripts/java.base-list.txt \
              --linker-path ${DEVKIT}/bin/ld \
              --compile-with-assertions \
              --output \
              test.so \
              --class-name $(cat classes.txt) | tee test.so.log
      fi

      echo "=== running with +UseEmptySlotsInSupers (OK)"
      ${JAVA_HOME}/bin/java -Xshare:off -ea -esa -XX:+UnlockExperimentalVMOptions -XX:AOTLibrary=$(pwd)/test.so -XX:+UseEmptySlotsInSupers -version

      echo "=== running with -UseEmptySlotsInSupers (will get stuck)"
      ${JAVA_HOME}/bin/java -Xshare:off -ea -esa -XX:+UnlockExperimentalVMOptions -XX:AOTLibrary=$(pwd)/test.so -XX:-UseEmptySlotsInSupers -version
      ==========================================================================================

      $ bash doit.sh
      === running with +UseEmptySlotsInSupers (OK)
      java version "16-internal" 2021-03-16
      Java(TM) SE Runtime Environment (fastdebug build 16-internal+0-adhoc.iklam.open)
      Java HotSpot(TM) 64-Bit Server VM (fastdebug build 16-internal+0-adhoc.iklam.open, mixed mode, aot)
      === running with -UseEmptySlotsInSupers (will get stuck)
      ^C

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            Unassigned Unassigned
            iklam Ioi Lam
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              Updated:
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