RFR(M): 8141529: Fix handling of _JAVA_SR_SIGNUM

[David Holmes]

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.
>