RFR: 8042243: Map shared archive to preallocated static address

[David Holmes]

Hi Yumin,

For something that only addresses one platform this adds a lot of 
platform specific code to a bunch of shared files. Are there plans to 
extend this to other platforms? Otherwise can we make this more platform 
agnostic? Perhaps move the os specific code to the os class? Seems the 
changes in filemap.cpp and metaspace.cpp could easily be factored into 
an os method that returns a boolean to indicate whether there is a fixed 
mapping.

And perhaps define set_static_shared_space in the os class and always 
expose it via jni.cpp. Actually, why are we exposing this via jni.cpp 
rather than jvm.cpp? This is not part of the JNI interface to the VM.

Thanks,
David

On 6/05/2014 9:15 AM, Yumin Qi wrote:
> Hi, Please have codereview for
>
> 8042243: Map shared archive to preallocated static address
>
> webrev: http://cr.openjdk.java.net/~minqi/8042243/webrev00/
> bug: https://bugs.openjdk.java.net/browse/JDK-8042243
>
> Summary: Mapping shared archive (jsa) some time fail due to ASLR
> (Address space layout randomization) on 32bit Linux platforms. To solve
> we come up with mapping shared archive to preallocated static space
> since with Linux and the GCC compiler, the BSS section in the main
> executable is not randomized, instead, the variable address in the BSS
> section is fixed at build time. The tests also showed the extra 32M
> space will NOT affect java memory setting though it seems 32M virtual
> address space always allocated no matter it is used or not (If
> -XX:ShareBaseAddress supply alternative address for dumping, the static
> address will be ignored.) Note the changes is for 32 bit Linux only.
>
> Tests: JPRT, manual test for archive sharing.
>
> Thanks
> Yumin