Shenandoah JDK 8 backport crashes when running Cassandra

[Aleksey Shipilev]

Hi Amir,

On 2/5/20 3:23 PM, Amir Hadadi wrote:
> #  SIGSEGV (0xb) at pc=0x00007f2fd6a1a559, pid=102562, tid=0x00007f28885f7700
> #
> # JRE version: OpenJDK Runtime Environment (8.0) (build 1.8.0-builds.shipilev.net-openjdk-shenandoah-jdk8-b517-20191231)

Trying a bit more modern build would be a plus.

> ---------------  T H R E A D  ---------------
> Current thread (0x00007f27d8007620):  JavaThread "ReadStage-2" daemon [_thread_in_Java, id=103716, stack(0x00007f28885b7000,0x00007f28885f8000)]
> siginfo: si_signo: 11 (SIGSEGV), si_code: 1 (SEGV_MAPERR), si_addr: 0x000000000000000f
> Registers:
> RAX=0x0000000000000000, RBX=0x000000000000000d, RCX=0x0000000000000008, RDX=0x0000000000000010
> RSP=0x00007f28885f6090, RBP=0x00007f28885f63e8, RSI=0xffffffffffffffff, RDI=0x0000000000000010
> R8 =0x000000000000000f, R9 =0x0000000000000000, R10=0x00007f2fed1b5360, R11=0x00007f2f4c6f7d18
> R12=0x0000000000000000, R13=0x0000000000560040, R14=0x00007f28885f6408, R15=0x00007f27d8007620
> RIP=0x00007f2fd6a1a559, EFLAGS=0x0000000000010207, CSGSFS=0x0000000000000033, ERR=0x0000000000000006
>   TRAPNO=0x000000000000000e
> Instructions: (pc=0x00007f2fd6a1a559)
> 0x00007f2fd6a1a539:   01 00 00 48 8b bc 24 08 01 00 00 4c 03 c7 48 b8
> 0x00007f2fd6a1a549:   00 00 00 00 00 00 00 00 4c 8b 8c 24 d8 00 00 00
> 0x00007f2fd6a1a559:   4e 89 0c 00 48 81 c4 30 01 00 00 5d 85 05 95 7b
> 0x00007f2fd6a1a569:   5c 17 c3 48 8b 94 24 e8 00 00 00 48 8b b4 24 e0

This decodes to:

 48 b8 00 00 00 00 00 00 00 00    movabs rax,0x0
 4c 8b 8c 24 d8 00 00 00          mov    r9,QWORD PTR [rsp+0xd8]
 4e 89 0c 00                      mov    QWORD PTR [rax+r8*1],r9 <--- crash here
 48 81 c4 30 01 00 00             add    rsp,0x130

The prior store of literal zero to %rax is weird, is that a code root or a C1 patch going wrong?

How reproducible is this? Are there specific steps to reproduce?

Please try with -XX:+ShenandoahVerify and/or fastdebug builds.

-- 
Thanks,
-Aleksey