RFR: JDK-8302320: AsyncGetCallTrace obtains too few frames in sanity test

[David Holmes]

On Wed, 15 Feb 2023 07:10:29 GMT, Johannes Bechberger <duke at openjdk.org> wrote:

>> From `frame_x86.hpp`:
>> 
>>   // The interpreter and adapters will extend the frame of the caller.
>>   // Since oopMaps are based on the sp of the caller before extension
>>   // we need to know that value. However in order to compute the address
>>   // of the return address we need the real "raw" sp. By convention we
>>   // use sp() to mean "raw" sp and unextended_sp() to mean the caller's
>>   // original sp.
>> 
>> by that definition `unextended_sp` is always > `sp`. If something has violated that definition/convention then we may have bigger problems!
>
> I get the following values for `sp` and `unextended_sp` when running this test case:
> 
> 
> int sp = 0x7f9f1ec614e0, unextended sp = 0x7f9f1ec614e0
> int sp = 0x7f9f1ec61538, unextended sp = 0x7f9f1ec61548
> int sp = 0x7f9f1ec615a0, unextended sp = 0x7f9f1ec61598 // the assumption fails here
> int sp = 0x7f9f1ec61600, unextended sp = 0x7f9f1ec61608
> int sp = 0x7f9f1ec61670, unextended sp = 0x7f9f1ec61688
> ...

What is the test case? Is it sending signals and then using AGCT? If so then maybe a signal hits when a call is made but before the code has a chance to update unextended_sp?

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PR: https://git.openjdk.org/jdk/pull/12535