RFR: JDK-8254189: Improve comments for StackOverFlow and fix in_xxx() functions

[Thomas Stuefe]

On Tue, 27 Oct 2020 01:27:24 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> Hi,
>> 
>> may I please have reviews for this small cleanup / fix?
>> 
>> While reviewing JDK-8253717 it was found that comments would help with understanding the StackOverFlow class. Especially the fact that the various _base_ are actually pointing outside their respective zone, since the stack grows downward and a zone (and the stack itself) range is [end, base). If you don't look at this code daily it can be surprising.
>> 
>> This also fixes some small off-by-one errors in various "in_stack_xxx_zone()" methods which test whether a given address is inside a zone and gave wrong results for address=base since base points outside its zone. This had the effect that an address could be in multiple zones.
>> 
>> Finally it adds a small gtest which tests the StackOverFlow methods.
>
> src/hotspot/share/runtime/stackOverflow.cpp line 44:
> 
>> 42:   // Note: Zone sizes are given via Stack(Red|Yellow|Reserved|Shadow)Pages
>> 43:   //  parameters; these names are misleading since they actually contain
>> 44:   //  zone size in units-of-4K-size, regardless the actual platform page size,
> 
> s/regardless the/regardless of the/
> 
> But this is already covered by the following comment:
> 
>   // We need to adapt the configured number of stack protection pages given
>   // in 4K pages to the actual os page size. We must do this before setting

Okay, I'll remove the comment.

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PR: https://git.openjdk.java.net/jdk/pull/795