RFR(M): 8221077: No NullPointerException message if top frame is hidden.

[David Holmes]

Hi Remi,

On 7/05/2019 12:39 am, Remi Forax wrote:
> Hi Goetz,
> please don't !
> 
> You have existing codes that behave differently depending on the caller class,
> part of the security model is based on that, but also other APIs like by example, many of the existing logging libraries.
> 
> When a stack frame is hidden, it means that the stack frame is not visible for getCallerClass, the StackWalker API and the Throwable stacktrace,
> the VM/JDK offers one coherent view of the stack frames.

I would argue that "throwable stacktrace" has different considerations 
if the exception is actually thrown due to an error in the code in the 
"hidden frame". Otherwise you will get messages about impossible exceptions.

> If you suppress the hiding for one of these entry points, at best, applications will fail, at worst you have introduced a security issue.

The suppression would need to be selective - unless you're claiming that 
anything that shows these hidden frames exist could be considered a 
security issue?

Cheers,
David
-----

> regards,
> Rémi
> 
> ----- Mail original -----
>> De: "Goetz Lindenmaier" <goetz.lindenmaier at sap.com>
>> À: "David Holmes" <david.holmes at oracle.com>, "hotspot-runtime-dev" <hotspot-runtime-dev at openjdk.java.net>, "Coleen
>> Phillimore (coleen.phillimore at oracle.com)" <coleen.phillimore at oracle.com>
>> Envoyé: Lundi 6 Mai 2019 14:36:36
>> Objet: RE: RFR(M): 8221077: No NullPointerException message if top frame is hidden.
> 
>> Hi David,
>>
>> I'm not really happy with the design of hiding the frames,
>> either.
>> For 'inner' frames this seems ok, but for the top frames
>> up to the first not-hidden frame it is questionable to
>> hide them.  As you say, there might be exceptions where
>> this is desirable, for NPE it seems wrong.
>>
>> I’ll have a look how it could be implemented to
>> suppress the hiding in case of NPE.
>>
>> Best regards,
>>   Goetz.
>>
>>
>>> -----Original Message-----
>>> From: David Holmes <david.holmes at oracle.com>
>>> Sent: Montag, 6. Mai 2019 13:50
>>> To: Lindenmaier, Goetz <goetz.lindenmaier at sap.com>; hotspot-runtime-
>>> dev at openjdk.java.net; Coleen Phillimore (coleen.phillimore at oracle.com)
>>> <coleen.phillimore at oracle.com>
>>> Subject: Re: RFR(M): 8221077: No NullPointerException message if top frame is
>>> hidden.
>>>
>>> Hi Goetz,
>>>
>>> Just commenting on the situation ...
>>>
>>> On 6/05/2019 8:22 pm, Lindenmaier, Goetz wrote:
>>>> Hi,
>>>>
>>>> Exceptions can print the stack trace of when the exception occurred.
>>>> There can be methods on the stack that have been generated by
>>>> the runtime. To not confuse the reader of the stackTrace,
>>>> these are omitted (if -XX:-ShowHiddenFrames, which is default.)
>>>>
>>>> If the top frame is omitted/hidden,
>>>> it is inconsistent to print a message telling where
>>>> exactly in the hidden method the error occurred.
>>>>
>>>> Further, if the top frame is hidden, the information
>>>> needed to compute the message is missing. A wrong
>>>> message will be printed.
>>>>
>>>> This change suppresses the NPE message if the NPE
>>>> occurred in a hidden top frame.
>>>
>>> This sounds to me like "hidden frames" are being applied too broadly.
>>> Frames should only be hidden with respect to throwing specific
>>> exceptions - those for which the frame is  part of the "throwing
>>> mechanics". If that code hits a real exception then the frame should not
>>> be treated as hidden IMO. But I don't know whether we can clearly
>>> identify which kinds of exceptions should really lead to a frame being
>>> hidden.
>>>
>>> David
>>> -----
>>>
>>>> It adds a java.lang.Boolean(true) to the backtrace
>>>> in case the real top frame is a hidden one and is dropped.
>>>>
>>>> When the NullPointerException message text is generated, this is
>>>> checked and the message is skipped if the proper frame is not
>>>> available.
>>>>
>>>> I handle this in a bug itself to keep the discussion of
>>>> the basic feature separated from this technical issue.
>>>>
>>>> Please review:
>>>> https://bugs.openjdk.java.net/browse/JDK-8221077
>>>> http://cr.openjdk.java.net/~goetz/wr19/8221077-hidden_top_frame/02/
>>>> This change must be applied on top of
>>>> http://cr.openjdk.java.net/~goetz/wr19/8218628-exMsg-NPE/08/
>>>>
>>>> Best regards,
>>>>     Goetz.