RFR(XS): 8193308: Disallow installing user signal handlers for SIGBUS on OSX

[David Holmes]

On 10/02/2018 5:18 PM, mandy chung wrote:
> On 2/9/18 8:53 PM, David Holmes wrote:
>> Hi Mandy,
>>
>> On 10/02/2018 9:14 AM, mandy chung wrote:
>>> (fixed formatting)
>>>
>>> As documented in [1], SIGBUS is listed as the signals used by the 
>>> HotSpot implementation. It could be just that it was missed from day 1.
>>
>> That document has not been well maintained, nor does it accurately 
>> reflect the actual implementation details.
>>
> 
> It should be updated.  Please file a doc issue to include specific 
> change.  I find the current form quite reasonable.
> 
>>> Have you checked the native signal chaining support via libjsig.so? 
>>> It should disallow to install a user native signal handler for SIGBUS.
>>>
>>> I think JVM_RegisterSignal should disallow installing a user handler 
>>> for one of the implementation-specific signals for all platforms. 
>>> That'll simplify your fix.  I would think the compatibility risk 
>>> should be low as rare cases would want to intercept SIGBUS which is 
>>> also clearly documented in [1].
>>
>> Each platform defines its own set of signals that are used by the VM 
>> on that platform. While I've never thought it made any sense to 
>> attempt to install user "handlers" for SIGBUS or SIGSEGV (not that we 
>> allow the latter) others have argued that unless we use it then we 
>> should allow it. Hence no "lowest common denominator" approach - 
>> though that certainly would be simpler.
>>
>> In this case I believe it is simply another case where the OS X port 
>> copied the Linux code and it wasn't realized that OS X would generate 
>> SIGBUS when SIGSEGV is "expected" and so didn't list it as excluded.
> 
> Are we agreeing on disallowing SIGBUS for all platforms?

No. If the VM doesn't use SIGBUS on a platform then it shouldn't 
disallow it.

David

> Mandy