Details

    • Type: Bug
    • Status: Resolved
    • Priority: P2
    • Resolution: Fixed
    • Affects Version/s: 1.3.1
    • Fix Version/s: 1.3.1_04
    • Component/s: hotspot
    • Labels:
    • Subcomponent:
    • Resolved In Build:
      04
    • CPU:
      sparc
    • OS:
      solaris_8

      Backports

        Description



        Name: kb87695 Date: 04/05/2001


        The Solaris 131 hotspot VM fails with javac test
        case of jvm98 version 1.03_05 19981203. In the default version, this bug
        is pretty sporadic and does not happen always. If we stress the VM
        with -Xcomp and -XX:+ScavengeALot and -XX:+FullGCALot with both
        intervals set as 1000, we can reproduce it quite reliably.

        Case 1:

        This is a solaris compiler bug that presents itself in SPECjvm tests
        running _213_javac. In the normal mode it runs fine. However, if we
        stress the VMwith excessive compilation and excessive scavenging
        and gcing, the VM fails in various sort of ways. These effects are not
        in the -Xint mode.

           1. It could get a signal and core dump.
           2. It gets a broken oop and then halts(we run with
                -XX:+VerifyOops).
           3. Starts giving out incorrect warnings and errors
                from the javac program. In the normal run, no
                such warnings or errors are produced.

        I am giving the required command line that produces the bug and
        the tail of a log file of the output. We have to use the debug build
        in order to get the appropriate flags that stress the VMappropriately.
        The bug appears after about an hour or so.

        Going to the top directory of jvm98, just fire
        off.

        $ java_g -Xcomp -XX:+PrintCompilation
        -XX:+ScavengeALot-XX:ScavengeALotInterval=1000 -XX:+VerifyOops
        -XX:+FullGCALot -XX:FullGCALotInterval=1000 -Xmx256m -Xms256m
        SpecApplication -s100 -M4 -m4 -g -d3000 -a _213_javac

        The tail of the output is like this:

        Full gc no: 51 Interval: 783
        1447 b spec.benchmarks._213_javac.ArrayExpression::checkInitializer (108 bytes)
        1448 b spec.benchmarks._213_javac.BinaryLogicalExpression::checkValue (32
        bytes)
        1449 b spec.benchmarks._213_javac.ExprExpression::checkCondition (26 bytes)
        1450 b spec.benchmarks._213_javac.AndExpression::checkCondition (90 bytes)
         EXECUTION STOPPED: verify_oop: L3: broken oop

        verify_oop: L3: broken oop
        Execution stopped, print registers?
        # SafepointSynchronize::begin: Fatal error:
        # SafepointSynchronize::begin: Timed out while attempting to reach a safepoint.
        # SafepointSynchronize::begin: Threads which did not reach the safepoint:
        # nid=0x1 runnable
        # SafepointSynchronize::begin: (End of list)


        Case 2:

        I think that an incorrect oopmap has been created by the
        compiler and thus is not properly updated by the garbage
        collector. I have also created a slight modification to the
        code and then caused this bug to appear in a small test case.
        This breaks the modified VM instantaneously.

        I.) The Change in the solaris code.
                              < instruct checkCastPP( iRegP dst) %{
                              < match(Set dst (CheckCastPP dst));
                              < format %{ "#checkcastPP of $dst" %}
                              < ins_encode( /*empty encoding*/ );
                              < ins_pipe(empty);
                              ---
                              > instruct checkCastPP( iRegP dst, iRegP src) %{
                              > match(Set dst (CheckCastPP src));
                              > format %{ "#checkcastPP of $dst <- $src" %}
                              > ins_encode( form3_g0_rs2_rd_move( src, dst )
        );
                              > ins_pipe(ialu_reg);

        I guess this change should not change the
        correctness of the VM code generated,
        although it does produce inefficient code with
        redundant instructions.

         II.) The test case:
         /* Run this application in this form
        $ java_g -Xcomp -XX:CompileOnly=.Test -XX:-Inline -XX:NewSize=1048576 -XX:+PrintScavenge -XX:+PrintCompilation
        GcOopTest
         */
        public class GcOopTest {
           public static final int ARRAY_SIZE = 1000000;
           public static void doGC(byte[] byteArray, int size) {
                  int [] forceSvavengeArray = new int[size/2];
                  for(int i = 0; i < size; i++) {
                        byteArray[i] = 10;
                   }
                   //System.gc();
           }
           public static boolean Test(int size) {
                 size = size/2;
                 byte [] byteArray = new byte [size];
                  for(int i = 0; i < size; i++) {
                       byteArray[i] = 1;
                  }

                  doGC(byteArray, size);

                  for(int i = 0; i < size; i++) {
                        if(byteArray[i] != 10)
                        return false;
                  }
                  return true;
          }

          public static void main(String[] args) {
              int size = ARRAY_SIZE;
              char [] a = new char [1];
              byte [] b = new byte [1];
              a[0] = 1;
              b[0] = 1;
              boolean test = false;
              if((test = Test(size)) == true)
                  System.out.println("Ok");
              else
              System.out.println("Error");
           }
        }

        III.) The output of the test (incorrect). If the
        output is Ok, then it is correct.

        $ java_g -Xcomp -XX:CompileOnly=.Test -XX:-Inline -XX:NewSize=1048576 -XX:+PrintScavenge -XX:+PrintCompilation GcOopTest
                              VM option 'CompileOnly=.Test'
                              VM option '-Inline'
                              VM option 'NewSize=1048576'
                              VM option '+PrintScavenge'
                              VM option '+PrintCompilation'
                                1 b GcOopTest::Test (55 bytes)
                              [GC 635K->572K(2368K), 0.1161145 secs]
                              Error

        This shows an incorrect run.

        IV) The opto-assembly dump.
         I have also attatched the OptoAssembly dump of the
        method concerned. Please notice my comments around basic
        block B20. They are encapsulated with << Manosiz ... >>. There
        is a copy of register R_L4 to R_L2 done by the CheckCastPP
        code.

        Even though in the oopmap that is generated at the
        safepoint (method entry point) contains only R_L2, we use R_L4
        after we come back from the method call. If during the time
        between the called method and its return a scavenge occurs and
        objects get moved, only R_L2 will be patched and not R_L4. And hence the bug.

        At the compiled method, we will be pointing at the old object, while the
        new object has already been moved.

        In short this is what happened.
        1. The compiled method does not inline anything.
        Thus doGC is a interpreter call.

        2. In the compiled method the oopmap only marks
        R_L2 as holding the only oop, while R_L4 also contains an oop.

        3. After we enter the interpreted method, due to
        the reduced size of the new generation space, a scavenge occurs which
        moves the related oop.

        4. The pointer in R_L2 is updated according to the
        oopmap but R_L4 is not.

        5. We return back to the compiled code and use
        R_L4 and see ourselves pointing at the old oop and not the new one.


          
        (Review ID: 120072)
        ======================================================================

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                • Assignee:
                  cclicksunw Clifford Click (Inactive)
                  Reporter:
                  kevibrow Kevin Brown
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