RFR(S) 8205965: SIGSEGV on write to NativeCallStack::EMPTY_STACK

[Martin Buchholz]

Zhengyu,

Thanks for fixing this!

I would have tried to use *Construct On First Use Idiom*
https://isocpp.org/wiki/faq/ctors#static-init-order-on-first-use
but nothing here is easy, unlike in Java with its static finals.
(and I'm not (yet) a hotspot engineer)


On Fri, Jun 29, 2018 at 6:04 AM, Zhengyu Gu <zgu at redhat.com> wrote:

> Hi,
>
> clang-6.0 and above, can deduce that NativeCallStack::EMPTY_STACK is all
> zeros, and since it is a static constant, it places the object in the
> read-only BSS data section.
>
> To workaround static initialization ordering issue, NMT has to ensure
> EMPTY_STACK is initialized before turns itself on, which can happen in the
> middle of initialization of other static objects. In this case, it causes
> SIGSEGV while try to write to the read-only memory.
>
> The solution is to make EMPTY_STACk private and non-constant, but hands
> out constant version.
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8205965
> Webrev: http://cr.openjdk.java.net/~zgu/8205965/webrev.00/
>
> Test:
>
>   hotspot_nmt on Linux 64 (fastdebug and release)
>
> Thanks,
>
> -Zhengyu
>