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

[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, there is old
code being executed to work around the exec shield CS limit. That code
depends on the initial stack size being captured. Right now this is
undefined code: Pointer artithmetic on NULL pointer.

src/hotspot/os_cpu/linux_x86/os_linux_x86.cpp:884:73: runtime error: pointer index expression with base 0x00000000 overflowed to 0xffffb000

I propose to not perform the optimization of JDK-8199717 for Linux x32.

Bug: https://bugs.openjdk.java.net/browse/JDK-8221639
webrev: http://cr.openjdk.java.net/~sgehwolf/webrevs/JDK-8221639/01/webrev/

Testing: release/fastdebug builds on x32 Linux, inspecting
-Xlog:os=info messages, currently running through jdkd/submit. Tier 1
tests on Linux x86_64

Thoughts?

Thanks,
Severin