RFR: 8221639: [x32] expand_exec_shield_cs_limit workaround is undefined code after JDK-8199717

[Florian Weimer]

* David Holmes:

> On 24/04/2019 11:33 pm, Florian Weimer wrote:
>> * Severin Gehwolf:
>>
>>> Hi,
>>>
>>> Could I please get reviews for this Linux x32 fix? JDK-8199717 added a
>>> performance optimization to only capture the initial stack size when
>>> launched via non-java launchers. However, on Linux x32,
>>
>> Do you mean actual x32, or i386?  These two are different.
>
> The code is selected based on the IA32 define which is set for a
> detected architecture of "i?86" as returned by uname I presume.
>
> I had assumed this was simply equivalent to 32-but x86, but apparently
> x32 is something else.
>
>> Can you actually verify changes in this area?  I think it's pretty hard
>> these days to find a machine that actually uses the CS hack to avoid
>> universal read-implies-exec.  I don't think this was ever part of any
>> mainline kernel.
>
> According to:
>
> https://bugs.openjdk.java.net/browse/JDK-8023956
>
> A number of mainline kernels were affected:
>
> "RHEL 5 & 6 are affected, and earlier Ubuntu releases 10.04 (LTS),
> 11.04, and 12.04 have also taken in the patch. "

I meant mainline as in kernel.org.

The RHEL 6 kernel requires PAE, so you need to find a box which supports
PAE but not NX.  These are more common than I expected (at least in our
labs).  So the changes should indeed be testable, and the CS limit
workaround may still be needed.

Thanks,
Florian