RFR(S) 8243506 SharedBaseAddress is ignored by -Xshare:dump

[Calvin Cheung]

Hi Ioi,

Just couple of minor comments:

metaspaceShared.cpp:

336   // We don't want any valid object to be at the very of the archive.

" ... the very of ..." -> "... the very bottom of..." ?

SharedBaseAddressOption.java:

   77         // a top archive specified in the base archive position
   78         run2(topArchiveName, baseArchiveName,

It looks like the order of the top and base archives are not reversed.

Because the topArchiveName is used for dumpBaseArchive in line 65 and 
the order of the archives specified for dump2 (line 70) are the same as 
above (line 78). So the topArchiveName actually refers to the base archive?

thanks,

Calvin

On 5/5/20 11:40 AM, Ioi Lam wrote:
> https://bugs.openjdk.java.net/browse/JDK-8243506
> http://cr.openjdk.java.net/~iklam/jdk15/8243506-SharedBaseAddress-ignored.v01/ 
>
>
> -XX:SharedBaseAddress was essentially ignored due to a bug in
> JDK-8231610 [1].
>
> This fix will enhance both the flexibility and security of CDS.
>
>
> After this fix, -XX:SharedBaseAddress=N will have the following effect:
>
> N != 0
>
>   CDS archive written with a base address of N. If -XX:SharedBaseAddress
>   is not specified, we will use a default address (0x8_00000000 on
>   64-bit OS).
>
>   At run time, we will first attempt to map the CDS archive at N. If this
>   fails (the OS doesn't have enough contiguous free space at N), we will
>   map the CDS archive at a suitable location picked by the OS.
>
>   Specifying a non-default address could be useful:
>   - for diagnosing purposes
>   - if the default address is already occupied for some reason on your
>     environment, but you have another location that's always free.
>
> N == 0
>
>   At run time, the CDS archive will always be mapped to an address
>   selected by the OS.
>
>   This is useful for improved security -- on OSes that support ASLR 
> (Address
>   Space Layout Randomization), the address of the archived metaspace 
> objects
>   will be randomized on every run to make attacks more difficult.
>
>
> I have added checks to make the code more robust in handling arbitrary 
> values
> of N. See new tests in 
> cest/hotspot/jtreg/runtime/cds/SharedBaseAddress.java,
> and MetaspaceShared::initialize_dumptime_shared_and_meta_spaces().
>
>
> Thanks
> - Ioi
>
> ------
>
> [1] https://bugs.openjdk.java.net/browse/JDK-8231610
>     Relocate the CDS archive if it cannot be mapped to the requested 
> address