RFR: 8134396: Check upper limit of flags setting numbers of stack protection pages.

[gerard ziemski]

hi Goetz,

I have an upcoming patch that addresses stack pages and all the other runtime flags that have their ranges/constraints 
unimplemented. Could you withdraw your change for the moment and give me a chance to get my (large) commit in and then 
we can verify that your concerns are met please?


cheers

On 08/25/2015 07:35 AM, Lindenmaier, Goetz wrote:
> Hi,
>
> I detected a problem with the values of the flags setting the numbers of stack protection pages.
> TestOptionsWithRanges shows that illegal values for red and yellow pages are possible.
>
> In JavaThread::create_stack_guard_pages(),
> setting StackRedPages=92233720368547753 and StackYellowPages=1 yields
>
> len = (92233720368547753 + 1) * os::vm_page_size()
>      = 0x8000000000000000 * os::vm_page_size()
>      = 0
>
> Thus not protecting any pages of the stack.
>
> The check in os::init_2() succeeds, as there the Shadow pages are considered, too, so that the overflowed value is > 0.
>
> On linux, the VM stops with the misleading message
> "OpenJDK 64-Bit Server VM warning: Attempt to allocate stack guard pages failed."
> On aix, we get assertions and SIGSEGVs.
>
> This fix implements a ConstraintFunc for the three flags involved, checking that no overflow
> can happen. This is a very nice new feature!
> http://cr.openjdk.java.net/~goetz/webrevs/8134396-StGPg/webrev.01/
>
> Please review this change.  I please need a sponsor.
>
> Alternatively, one could set a smaller upper limit in the range.  This limit would have to be small
> enough to fulfill the property for any page size possible on 32 bit systems.
>
> Best regards,
>    Goetz.
>
>
>