RFR(S): 8186286: [BSD] Primary thread's stack size is reported incorrectly

[David Holmes]

Hi Gunter,

On 18/08/2017 1:01 AM, Haug, Gunter wrote:
> Thanks for the review, Aleksey and Thomas
> 
> You’re right, it is much nicer to use the macros. I’ve updated the change accordingly:
> http://cr.openjdk.java.net/~ghaug/webrevs/8186286.v1

I'm unclear about the logic change here. If you round down then there is 
a chance you will enter the following if-block where otherwise you would 
not.

  915     *size = align_down(*size, getpagesize());
  916
  917     if ((*size) < (DEFAULT_MAIN_THREAD_STACK_PAGES * 
(size_t)getpagesize())) {

Have you verified with a range of aligned and unaligned stack sizes 
around that threshhold that everything works okay?

Some typos in the comment block:

alligned -> aligned
boundries -> boundaries
I round -> We round

> @Thomas: os::vm_page_size() is not used in current_stack_region(), I think because of initialization dependencies.

I don't see the dependency. It requires that it only be used after 
os::init() has been called. AFAICS the first time we will use this logic 
is when we attach the main thread, which happens after os::init().

Thanks,
David

> Best regards,
> Gunter
> 
> From: Thomas Stüfe <thomas.stuefe at gmail.com>
> Date: Thursday, 17. August 2017 at 15:06
> To: "Haug, Gunter" <gunter.haug at sap.com>
> Cc: "hotspot-dev at openjdk.java.net" <hotspot-dev at openjdk.java.net>
> Subject: Re: RFR(S): 8186286: [BSD] Primary thread's stack size is reported incorrectly
> 
> Hi Gunter,
> 
> 
> On Thu, Aug 17, 2017 at 2:24 PM, Haug, Gunter <gunter.haug at sap.com<mailto:gunter.haug at sap.com>> wrote:
> Hi,
> 
> can I please have reviews and a sponsor fort the following small bug fix:
> http://cr.openjdk.java.net/~ghaug/webrevs/8186286/
> https://bugs.openjdk.java.net/browse/JDK-8186286
> 
> At least on Mac OS 10.12 we have observed stack sizes of the primary thread not aligned to pages boundries. This can be provoked by e.g. setrlimit() (ulimit -s xxxx in the shell).This voids the computation of the addresses of the guard pages.
> 
> Fix:
> Apparently Mac OS actually rounds upwards to next multiple of page size however, it is conservative to round downwards here to be on the safe side.
> 
> Thanks and best regards,
> Gunter
> 
> Thanks for the patch!
> 
> Very minor nits: what Alexey wrote (we also have "is_aligned"). Plus, any reason not to use os::vm_page_size()? Initialization dependencies?
> 
> Kind Regards, Thomas
> 
> 
>