[9] RFR(L) 8166413: Integrate VM part of AOT changes

[Christian Thalinger]

> On Oct 27, 2016, at 10:11 PM, Andrew Haley <aph at redhat.com> wrote:
> 
> On 27/10/16 23:02, Christian Thalinger wrote:
> 
>> John and I discussed this before we decided to go with standard
>> formats.  The biggest issue with the current CDS archive is that
>> it’s not relocatable.  That means if the address you want to map at
>> is not available you’re out of luck.
> 
> Is that really an issue in practice?

Yes, I’ve seen this a lot on my MacBook in the past (interestingly not anymore) when first looking into storing interned strings in the CDS archive for AOT.  Also with address space layout randomization (ASLR) on Linux it can happen pretty easily.

It happens for people:

https://www.google.com/#q=java+unable+to+use+shared+archive

and usually they don’t know why.

> 
>> So, the proprietary CDS format needs to become relocatable; pretty
>> much make it a DSO.  And then you’re just reinventing the wheel.
>> Also, every operating system had decades to tune loading and linking
>> their format while you have to do it yourself.
> 
> They have, but what they have is still not so efficient: think about
> GOTs, PLTs, etc.  These work, but we do better in JIT-generated code.
> In other words, being as good as existing DSO formats is a very low
> bar.

Maybe you are right.

> 
> Andrew.