RFR (XS) 8216977: ShowHiddenFrames use in java_lang_StackTraceElement::fill_in appears broken

[coleen.phillimore at oracle.com]

On 8/29/19 1:33 AM, David Holmes wrote:
> Hi Coleen,
>
> On 29/08/2019 1:19 pm, coleen.phillimore at oracle.com wrote:
>> On 8/28/19 9:36 PM, David Holmes wrote:
>>> Hi Coleen,
>>>
>>> On 29/08/2019 6:25 am, coleen.phillimore at oracle.com wrote:
>>>> Summary: Return NULL source file and negative line number for 
>>>> hidden frames.
>>>>
>>>> See bug for more details.   Ran hs tier1-3 on linux-x64-debug and 
>>>> tier1 on all platforms.
>>>
>>> This issue made my head spin. I think what you have done has taken 
>>> things back to a sane place where ShowHiddenFrames is not being used 
>>> to do whacky things unrelated to hidden frames.
>>>
>>>> open webrev at 
>>>> http://cr.openjdk.java.net/~coleenp/2019/8216977.01/webrev
>>>> bug link https://bugs.openjdk.java.net/browse/JDK-8216977
>>>
>>> src/hotspot/share/classfile/javaClasses.inline.hpp
>>>
>>> Okay - this code was reporting a specially encoded "line number" 
>>> that actually contained the BCI, but only if ShowHiddenFrames was 
>>> true. Getting rid of this is good because it has nothing to do with 
>>> hidden frames and there wasn't even a check that the current frame 
>>> was in fact hidden.
>>>
>>
>> Yes, it could have checked if method->is_hidden() give the special 
>> line number with bci encoded.   Maybe tools can print something 
>> useful with that information. StackTraceElement.toString() doesn't 
>> though.
>>
>>> If we want to report the BCI when no line number table exists then 
>>> that should be a specific enhancement to the API.
>>
>> I agree.
>>>
>>> ---
>>>
>>> src/hotspot/share/classfile/javaClasses.cpp
>>>
>>> Okay - this code was changing a NULL source file to "unknown" but 
>>> only if ShowHiddenFrames is true. Again getting rid of this is good 
>>> as it again has nothing to do with hidden frames.
>>>
>>> If we want to report "unknown" rather than NULL, then we should make 
>>> that change independent of ShowHiddenFrames.
>>>
>>
>> Calling it <Unknown> makes it inconsistent with the case where the 
>> source file is unknown, which java.lang.StackFrame prints.
>>> ---
>>>
>>> test/hotspot/jtreg/runtime/StackTrace/HiddenFrameTest.java
>>>
>>> Can you add a comment explaining why String::concat meets the 
>>> criteria of "null source file" and "no line number table", as it is 
>>> not at all obvious to me what that should be the case. Also is that 
>>> true if we disable the String concatenation use of lambda? If not we 
>>> should add the necessary -XX:+ flag to the @run line.
>>
>> I don't know what that flag is.  It might be a property.  I don't 
>> think we'd run all the tests with such a flag though so I think this 
>> is safe.
>
> Sorry was confusing different things. You're just using a method 
> reference to String::concat which will use lambda expressions under 
> the hood. I was thinking about the lambdification of string 
> concatenation which is completely different.

Oh, yes it is.

So I have to give credit to Goetz because I copied a lot of this test 
case from the upcoming Helpful NPE test.
>
>>>
>>> For completeness can you check that the NPE only has one frame if 
>>> -XX:-ShowHiddenFrames is used.
>>
>> Sure:
>>
>> http://cr.openjdk.java.net/~coleenp/2019/8216977.02/webrev/test/hotspot/jtreg/runtime/StackTrace/HiddenFrameTest.java.html 
>
>
> Thanks! One nit:
>
>             String arg = (String)args[0];
>
> No need for a cast there - args is an array of String.

Ok, will fix.

thanks!
Coleen
>
> No need for new webrev.
>
> Thanks,
> David
>
>
>>
>> Thanks,
>> Coleen
>>>
>>> Thanks,
>>> David
>>> -----
>>>
>>>> Thanks,
>>>> Coleen
>>