RFR: 8247201: Print potential pointer value of readable stack memory in hs_err file

[Stefan Karlsson]

Thanks, David.

StefanK

On 2020-06-09 15:36, David Holmes wrote:
> Hi Stefan,
>
> Looks good!
>
> Thanks,
> David
>
> On 9/06/2020 9:25 pm, Stefan Karlsson wrote:
>> Hi all,
>>
>> Please review this patch to print potential pointer value of readable 
>> stack memory in hs_err files.
>>
>> https://cr.openjdk.java.net/~stefank/8247201/webrev.01/
>> https://bugs.openjdk.java.net/browse/JDK-8247201
>>
>> I often see these lines in hs_err file:
>> stack at sp + 2 slots: 0x00007000042e6930 points into unknown 
>> readable memory: 7c cb b3 05 01 00 00 00
>>
>> and have to manually transpose the bytes to see if they match an 
>> important pointer value.
>>
>> I'd like to always print the full pointer value, if possible:
>> stack at sp + 2 slots: 0x00007000042e6930 points into unknown 
>> readable memory: 0x0000000105b3cb7c | 7c cb b3 05 01 00 00 00
>>
>> The suggested patch only prints this value if the dereferenced 
>> address is aligned, otherwise it skips it.
>>
>> Side-note: the code that determines if the memory is readable only 
>> checks 4 bytes. So if we have a pointer at the end last few bytes of 
>> a page, and an inaccessible page after that, it seems like the 
>> pre-existing code will crash.
>>
>> Thanks,
>> StefanK