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  1. JDK
  2. JDK-8282773

Refactor parsing of integer VM options

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Details

    • Enhancement
    • Resolution: Fixed
    • P4
    • 19
    • 19
    • hotspot
    • b15

    Description

      When a VM option is given an integer value (e.g., -XX:ActiveProcessorCount=123), the set_numeric_flag function in arguments.cpp is called:

      https://github.com/openjdk/jdk/blob/cde923dd471a22cd69ea2cd4994bb16eba780804/src/hotspot/share/runtime/arguments.cpp#L841

      The current implementation always calls strtoull() to get an unsigned 64-bit number, and then try to cast/truncate the result to the target type, and perform sign conversion as needed.

      This is cumbersome and buggy, because the target type (such as intx) may have different bit-widths in different builds. Also, manual casting of unsigned to sign values can run into corner cases.

      ====================================================

      Proposed design: use C++ templates and SFINAE to automatically choose the correct function for parsing the input string. The VM should avoid doing cast and size conversion as much as possible.

      Also use a similar technique to write a comprehensive set of test cases to validate the implementation.

      ====================================================

      Here are existing bugs (as of the above version)

      (1) linux-x86/x64: ActiveProcessorCount is an int, but the VM doesn't catch the underflow:

      $ ./images/jdk/bin/java -XX:ActiveProcessorCount=-0x80000001
      Error occurred during initialization of VM
      Too large parallelism for remembered sets.

      (2) linux-x86: CICompilerCount is an intx (signed 32-bit), but the VM doesn't catch the overflow:

      $ ./images/jdk/bin/java -XX:CICompilerCount=1T
      CICompilerCount (0) must be at least 2
      Error: Could not create the Java Virtual Machine.
      Error: A fatal exception has occurred. Program will exit.

      (3) linux-x86: MetaspaceSize is a size_t (unsigned 32-bit), but the VM doesn't catch the overflow:
      $ ./images/jdk/bin/java -XX:MetaspaceSize=1234567812345678 -XX:+PrintFlagsFinal --version | grep size_t.MetaspaceSize
         size_t MetaspaceSize = 937885696 {product} {command line}


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              iklam Ioi Lam
              iklam Ioi Lam
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                Updated:
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