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

[刘希晨]

刘希晨 <benrush0705 at gmail.com> 于2023年8月18日周五 21:54写道：

> 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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