RFR(XS) 8087120: [GCC5] java.lang.StackOverflowError on Zero JVM initialization on non x86 platforms

[David Holmes]

On 10/06/2015 11:49 PM, Severin Gehwolf wrote:
> Hi,
>
> Could somebody please review this Zero only change? I'd also need a
> sponsor who can push the change for me once reviewed.
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8087120
> webrev: http://cr.openjdk.java.net/~sgehwolf/webrevs/JDK-8087120/webrev.01/
>
> The issue is that Zero relies on undefined behaviour for getting the
> current stack pointer by allocating a variable on the stack and
> returning its address. With GCC 5 returning an address of a local
> variable will always be 0, thus causing the issue. It worked fine with
> older GCC versions, because they returned the actual address of the
> variable.
>
> The fix is to use GCC's built-in function "__builtin_frame_address".
> This also works on GCC 5. It's GCC specific, though. On the other hand,
> I don't know if anybody builds Zero without GCC. An alternative would be
> to use alloca, but that has strange semantics if the stack pointer
> cannot be extended. Thoughts?

The Zero folk will need to confirm if this gcc dependency is ok or 
whether it requires an ifdef - and they can also push directly to one of 
the hotspot repos. Is the built-in available across gcc 4.x releases?

David

> Thanks,
> Severin
>