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

[mandy chung]

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?

Mandy