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

coleen.phillimore at oracle.com coleen.phillimore at oracle.com
Thu Aug 29 03:19:44 UTC 2019

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.
> For completeness can you check that the NPE only has one frame if 
> -XX:-ShowHiddenFrames is used.



> Thanks,
> David
> -----
>> Thanks,
>> Coleen

More information about the hotspot-runtime-dev mailing list