RFR: integer overflow in marking code for large object arrays

[Per Liden]

Looks good!

Should we maybe keep the arrayOop.hpp part as an upstream patch?

/Per

On 2018-02-12 17:10, Stefan Karlsson wrote:
> Hi all,
> 
> Please review this patch to fix an integer overflow bug in the marking 
> code for large object arrays.
> 
> http://cr.openjdk.java.net/~stefank/zgc/zLargeObjectArrayMarkingBug/webrev.01/ 
> 
> 
> This bug was found with a micro stress tests (externally reported - not 
> open), which stresses the marking code for large object arrays.
> 
> With gc+marking=trace the overflow bug could be seen:
> 
> [12,763s][trace][gc,marking] GC(1) Array follow large: 
> 0x0000040005600018-0x00000400055ffff8 (18446744073709551584), middle: 
> 0x0000040005601000-0x00000400055ff000 (18446744073709543424)
> 
> where the size (18446744073709551584), or more easily read 
> 0xffffffffffffffe0, is an unexpectedly large value for this code.
> 
> The patch adds a new assert that catches this kind of problems. The 
> following program doesn't reproduce the original crash, but it triggers 
> the added assert:
> 
> $ java -Xlog:gc*,gc+stats=off -XX:+UseZGC -Xmx20g -Xms20g -cp . 
> TestLargeObjectArray 2147483644
> 
> public class TestLargeObjectArray {
>    public static void main(String [] args) {
>      Object [] object = new Object[Integer.parseInt(args[0])];
>      System.gc();
>    }
> }
> 
> Thanks,
> StefanK