Causing jvm crash when entering C2 compiling when using panama memaccess on macos

[刘希晨]

Sorry, I didn't add the crash report files in the first mail, then I send
another one with hs_err_pid and replay_pid file attached, hoping to be
fixed soon.

Maurizio Cimadamore <maurizio.cimadamore at oracle.com> 于2023年8月18日周五 21:46写道：

> Thanks for the report, this seems related to long loop optimizations.
> CC'ing Roland.
>
> Maurizio
> On 18/08/2023 14:43, 刘希晨 wrote:
>
>
> Hi guys, I came into a jvm crash problem when using native memory access
> when on my macbook with m1 pro, here is the minimum reproducible codes:
>
> public class CrashExample {
>     private static final VarHandle byteHandle = MethodHandles.memorySegmentViewVarHandle(ValueLayout.JAVA_BYTE);
>     private static final long len = 100;
>     private static final byte CR = (byte) '\r';
>     private static final byte LF = (byte) '\n';
>
>     public static void main(String[] args) {
>         for(int round = 0; round < 1000; round++) {
>             try(Arena arena = Arena.ofConfined()) {
>                 MemorySegment memorySegment = arena.allocateArray(ValueLayout.JAVA_BYTE, len);
>                 for(int i = 0; i < 100000; i++) {
>                     int index = i % 99;
>                     byteHandle.set(memorySegment, index, CR);
>                     byteHandle.set(memorySegment, index + 1, LF);
>                     byte[] bytes = readUntil(memorySegment, CR, LF);
>                 }
>             }
>         }
>     }
>
>     private static byte[] readUntil(MemorySegment segment, byte... separators) {
>         for(long cur = 0; cur <= segment.byteSize() - separators.length; cur++) {
>             if(matches(segment, cur, separators)) {
>                 return segment.asSlice(0, cur).toArray(ValueLayout.JAVA_BYTE);
>             }
>         }
>         return null;
>     }
>
>     public static boolean matches(MemorySegment m, long offset, byte[] bytes) {
>         for(int index = 0; index < bytes.length; index++) {
>             if ((byte) byteHandle.get(m, offset + index) != bytes[index]) {
>                 return false;
>             }
>         }
>         return true;
>     }
> }
>
>
> the matches() method try to judge if the memorysegment has the same
> content as bytes from offset index, the readUntil() method try to traverse
> the memorysegment until it finds the target separators, return the bytes it
> has traversed.
>
> in the main() method,  readUntil() method was tested multiple times to
> reach the C2 compiler, then it will cause the JVM to crash.
>
> Here is what I have find out:
> 1. Calling readUntil() method with a single byte will not cause the JVM to
> crash ( In our example, CR and LF were used, so there are two bytes)
> 2. On Windows and Linux, it works well, this example will only crash on
> MacOS, I don't know if x64 or arm CPU makes a difference, since I only have
> a arm-based macbook
> 3. It will only crash when entering C2 compiler phase, when the methods
> are not called so much times, they behave normally
> 4. crash seems to always happen in the # V [libjvm.dylib+0x139a2c]
> AddNode::IdealIL(PhaseGVN*, bool, BasicType)+0x48 or # V [libjvm.dylib+
> 0x958270] SubLNode::Ideal(PhaseGVN*, bool)+0xfc
>
> I have attached the crash report to the mail, I don't know if it's a
> problem about C2 compiler or Panama memaccess, cheers
>
>
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