[14] RFR(S): 8225653: Provide more information when hitting SIGILL from HaltNode

[Christian Hagedorn]

Hi Vladimir

Thank you for your review!

On 05.09.19 16:11, Vladimir Ivanov wrote:
> What do you think about reusing MacroAssembler::stop()? Otherwise, you 
> have to add MacroAssembler::halt for x86-32 as well.
> 

As we have discussed, this is another option to use 
MacroAssembler::stop() by changing the assert in 
MacroAssembler::debug32/64 into a guarantee() or fatal() to also crash 
with a message in a product build. This change should be possible as 
debug32/64 is currently only used in debug mode. I think choosing 
fatal() would be better because the halt reason will then show up in the 
hs_err file.

Which option is preferable?

Best regards,
Christian

> On 04/09/2019 10:43, Christian Hagedorn wrote:
>> Hi
>>
>> Please review the following patch:
>> https://bugs.openjdk.java.net/browse/JDK-8225653
>> http://cr.openjdk.java.net/~chagedorn/8225653/webrev.00/
>>
>> This enhancement provides more information about executing a HaltNode 
>> on x86. Up to now, an illegal instruction was emitted for a HaltNode 
>> which resulted in a crash with SIGILL at runtime if executed. This 
>> made it hard to determine if the crash was actually caused by a 
>> HaltNode or not without doing a closer analysis.
>>
>> This patch adds a string to each HaltNode stating the purpose of it. 
>> Code generation for a HaltNode adds a runtime call which executes 
>> fatal() with the newly provided HaltNode string. The VM then crashes 
>> with this additional information which should make a further analysis 
>> easier. I filed an RFE [1] to also provide this information for 
>> architectures other than x86.
>>
>> The assert at [2] is not necessary anymore since there is a new 
>> DEFINE_CLASS_ID entry for HaltNode with ID 15. ClassMask_Halt now 
>> equals USHORT_MAX, making the assert always true. It might be a good 
>> idea to file an RFE to change the current encoding as the next entry 
>> with ID 16 will exceed the 16 bit limit.
>>
>> Thank you!
>>
>> Best regards,
>> Christian
>>
>>
>> [1] https://bugs.openjdk.java.net/browse/JDK-8230552
>> [2] 
>> http://hg.openjdk.java.net/jdk/jdk/file/d8f22418ca99/src/hotspot/share/opto/node.hpp#l750 
>>