RFR: 8189170: Add option to disable stack overflow checking in primordial thread for use with JNI_CreateJavaJVM

[Thomas Stüfe]

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>


> Regarding this part of Thomas' review:
>
> Or, something like this:
> static bool is_primordial_thread(void) WINDOWS_ONLY({return false;})
> BSD_ONLY({return false;})
>
>
> I can do that. I'll see if anyone else has any comments on this.
>
>
> I'm assuming that Thomas means for the above to be at the
> platform independent layer (runtime/os.hpp?) so it is more
> obvious to the reader that the function doesn't do anything
> on those two platforms... I know we dislike such things at
> the platform independent layer, but it does feel appropriate
> to make this limitation more obvious.
>
> I would be okay if you made the change that Thomas is suggesting.
>
>
Yes, that's what I meant. Putting that into os.hpp makes it sprint up
readily, e.g. in Tooltips in Eclipse CDT when hovering over the function
call.

..Thomas


> Thumbs up!
>
> Dan
>
>
>
>
> There are three parts to this which made it somewhat more complicated than
> I had envisaged:
>
> 1. Add the flag and disable the guards.
>
> This is relatively straight-forward:
>
>  void JavaThread::create_stack_guard_pages() {
>    if (!os::uses_stack_guard_pages() ||
>        _stack_guard_state != stack_guard_unused ||
>        (DisablePrimordialThreadGuardPages && os::is_primordial_thread()))
> {
>        log_info(os, thread)("Stack guard page creation for thread "
>                             UINTX_FORMAT " disabled",
> os::current_thread_id());
>      return;
>
> with a tweak in JavaThread::stack_guards_enabled as well.
>
> 2. Promote os::XXX::is_initial_thread to os::is_primordial_thread()
>
> We have three platforms that already implement this functionality: Linux,
> Solaris and AIX. For BSD/OSX and Windows we don't attempt to do anything
> different for the primordial thread, and we don't have a way to detect the
> primordial thread - so is_primordial_thread() just returns false.
>
> I also tidied up some comments regarding terminology.
>
> 3. Thomas noticed that we unconditionally subtract 2*page_size() from the
> rlimit stack size, without checking it was bigger than 2*page_size() to
> start with. I was unsure how to tackle this. It's no good leaving
> stack_size at zero so I opted to ensure we would have at least one page
> left. Of course in such cases we would hit the bug in libc (if it still
> exists, which seems unlikely but time consuming to establish).
>
> Testing:
>   - Tier 1 (JPRT) testing with a modified launcher that uses the
> primordial thread
>     - with guard pages enabled
>     - with guard pages disabled
>   - Tier 1 (JPRT) normal JDK build (which should be unaffected by this
> change)
>
> The testing was primarily to ensure that disabling the stack guards on the
> primordial thread wasn't totally broken. A number of tests fail:
> - setting -Xss32m fails for the primordial thread when guards are enabled
> and the rlimit is 8m
> - tests that would hit StackOverflowError crash the VM when guards are
> disabled (as you would expect).
> - runtime/execstack/Testexecstack.java crashes when the guards are
> disabled
>
> Thanks,
> David
>
>
>