RFR(XXS): 8188109 JVM should print a warning message that -Xshare:on may cause VM to abort start-up

[David Holmes]

Hi Ioi,

Sorry but this troubles me ...

On 31/05/2018 9:39 AM, Ioi Lam wrote:
> https://bugs.openjdk.java.net/browse/JDK-8188109
> http://cr.openjdk.java.net/~iklam/jdk11/8188109-xshare-on-print-warning.v01/ 
> 
> 
> 
> Hi,
> 
> Please review this one-liner patch.
> 
> -Xshare:on may cause infrequent/intermittent start-up failure due to the 
> presence of Address Space Layout Randomization (ASLR). This option is 
> intended for testing (the internals of CDS) only and should not be used 
> in production environments.
> 
> With this patch, the following warning message is printed when 
> -Xshare:on is specified:
> 
> $ java -Xshare:on -version
> Java HotSpot(TM) 64-Bit Server VM warning: -Xshare:on is for testing 
> purpose only and may cause JVM start-up failure. Use -Xshare:auto instead.
> java version "11-internal" 2018-09-25
> Java(TM) SE Runtime Environment 18.9 (fastdebug build 
> 11-internal+0-adhoc.iklam.open)
> Java HotSpot(TM) 64-Bit Server VM 18.9 (fastdebug build 
> 11-internal+0-adhoc.iklam.open, mixed mode, sharing)

So should this warning only be enabled in product builds?

Even then it may be annoying for anyone who runs with -Xshare:on as 
they've set up CDS as documented [1][2] and they know their environment 
works ok - now they get a warning.

Also I'm unclear how "on" fails due to ASLR but "auto" keeps going?

Maybe only if the archive mapping fails and "on" was used then give a 
warning? Or just improve the message given when the VM aborts?


Thanks,
David

[1] 
https://docs.oracle.com/javase/10/vm/class-data-sharing.htm#JSJVM-GUID-0260F857-A70E-4399-A1DF-A5766BE33285
[2] 
https://docs.oracle.com/javase/10/tools/java.htm#JSWOR-GUID-31503FCE-93D0-4175-9B4F-F6A738B2F4C4

>     --- vs ---
> 
> $ java-Xshare:auto -version
> java version "11-internal" 2018-09-25
> Java(TM) SE Runtime Environment 18.9 (fastdebug build 
> 11-internal+0-adhoc.iklam.open)
> Java HotSpot(TM) 64-Bit Server VM 18.9 (fastdebug build 
> 11-internal+0-adhoc.iklam.open, mixed mode, sharing)
> 
> I am testing with HotSpot tiers 1-3 to make sure the tests don't get 
> tripped by this new warning message.
> 
> Thanks
> - Ioi