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

[David Holmes]

Hi Severin,

On 11/06/2015 6:05 PM, Severin Gehwolf wrote:
> Hi David,
>
> On Thu, 2015-06-11 at 15:45 +1000, David Holmes wrote:
>> 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.
>
> Speaking as the Zero maintainer, the GCC dependency is OK. I'd rather
> avoid the ifdef. Unfortunately, I am not a committer so cannot push it
> myself. I can ask Andrew Haley to push the fix for me once you're OK
> with it.

It is zero specific so I am fine with it if you are.

Thanks,
David

>> Is the built-in available across gcc 4.x releases?
>
> Looking at the oldest GCC manual I've found for the 4.x series it
> appears it's available since 4.0.4. A couple of examples:
> https://gcc.gnu.org/onlinedocs/gcc-4.0.4/gcc/Return-Address.html#Return-Address
> https://gcc.gnu.org/onlinedocs/gcc-4.1.2/gcc/Return-Address.html#Return-Address
> https://gcc.gnu.org/onlinedocs/gcc-4.5.4/gcc/Return-Address.html#Return-Address
> https://gcc.gnu.org/onlinedocs/gcc-4.9.2/gcc/Return-Address.html#Return-Address
> https://gcc.gnu.org/onlinedocs/gcc-5.1.0/gcc/Return-Address.html#Return-Address
>
> Thanks,
> Severin
>