RFR(M): 8141529: Fix handling of _JAVA_SR_SIGNUM

[Dmitry Samersoff]

David,

I think it's better to use NSIG (without underscore) defined in signal.h

-Dmitry


On 2015-11-12 10:35, David Holmes wrote:
> Hi Goetz,
> 
> Adding in serviceability-dev
> 
> On 9/11/2015 6:22 PM, Lindenmaier, Goetz wrote:
>> Hi,
>>
>> The environment variable _JAVA_SR_SIGNUM can be set to a signal number
>> do be used by the JVM's suspend/resume mechanism.
>>
>> If set, a signal handler is installed and the current signal handler
>> is saved to an array.
>> On linux, this array had size MAXSIGNUM=32, and _JAVA_SR_SIGNUM was
>> allowed
>> to range up to _NSIG=65. This could cause memory corruption.
>>
>> Further, in jsig.c, an unsinged int is used to set a bit for signals.
>> This also
>> is too small, as only 32 signals can be supported.  Further, the
>> signals are mapped
>> wrong to these bits.  '0' is not a valid signal, but '32' was.  1<<32
>> happens to map to
>> zero, so the signal could be stored, but this probably was not
>> intended that way.
>>
>> This change increases MAXSIGNUM to 65 on linux, and to 64 on aix. It
>> introduces
>> proper checking of the signal read from the env var, and issues a
>> warning if it
>> does not use the signal set.  It adapts the data types in jisig.c
>> properly.
>>
>> Please review this change.  I please need a sponsor.
>> http://cr.openjdk.java.net/~goetz/webrevs/8141529-NSIG/webrev.00
> 
> This all sounds very good to me. (I must find out why Solaris is not
> involved here :) ).
> 
> On Linux you didn't add the bounds check to os::Linux::set_our_sigflags.
> 
> I'm also wondering about documenting where we are determining the
> maximum from? Is it simply _NSIG on some/all distributions? And I see
> _NSIG is supposed to be the biggest signal number + one. Also linux
> defines NSIG = _NSIG so which should we be using?
> 
> Thanks,
> David
> 
>> Best regards,
>>    Goetz.
>>


-- 
Dmitry Samersoff
Oracle Java development team, Saint Petersburg, Russia
* I would love to change the world, but they won't give me the sources.