Take 2: RFR: 8197429: Increased stack guard causes segfaults on x86-32

[Andrew Haley]

On 14/02/18 02:10, David Holmes wrote:
> On 14/02/2018 12:51 AM, Andrew Haley wrote:
>> Webrev amended.
>>
>> http://cr.openjdk.java.net/~aph/8197429-2/
> 
> My question still stands:

Sorry, I didn't see it.

> How does this interact with the use of DisablePrimordialThreadGuardPages?

My initial answer was "not at all", but there is a minor possible
modification.  If DisablePrimordialThreadGuardPages is set it is
possible to use slightly more stack in Java code, so we could bang
down slightly further in workaround_expand_exec_shield_cs_limit() and
therefore place the codebuf slightly lower.  This would allow every
page of the primordial stack to be used in Java code.

Like this:

  if (os::is_primordial_thread()) {
    address limit = Linux::initial_thread_stack_bottom();
    if (! DisablePrimordialThreadGuardPages) {
      limit += JavaThread::stack_red_zone_size() +
        JavaThread::stack_yellow_zone_size();
    }
    os::Linux::expand_stack_to(limit);
  }

I'm happy to make that change and add a test for
DisablePrimordialThreadGuardPages if you think it's worth doing.

Alternatively, we could simply ignore the JVM's stack guard pages in
the calculation and always bang down all the way to
initial_thread_stack_bottom().  This would cause the codebuf to be
mapped slightly lower, but I guess that's no big deal.

-- 
Andrew Haley
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
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