Hi Chris,
Sorry for the delay.
On 13/11/2014 5:44 AM, Chris Plummer wrote:
Hi,
I'm still looking for reviewers.
As the change is to the launcher it needs to be reviewed by the launcher
owner - which I think is serviceability (though also cc'd Kumar :) ).
Launcher change, and your rationale, seems okay to me. I'd probably put
the test in to jdk/test/tools/launcher/ though.
Thanks,
David
thanks,
Chris
On 11/7/14 7:53 PM, Chris Plummer wrote:
This is an initial review for 6762191. I'm guessing there will be
recommendations to fix in a different way, but thought this would be a
good time to start the discussion.
https://bugs.openjdk.java.net/browse/JDK-6762191
http://cr.openjdk.java.net/~cjplummer/6762191/webrev.00.jdk/
http://cr.openjdk.java.net/~cjplummer/6762191/webrev.00.hotspot/
The bug is that if the -Xss size is set to something very small (like
16k), on linux there will be a crash due to overwriting the end of the
stack. This happens before hotspot can compute its stack needs and
verify that the stack is big enough.
It didn't seem viable to move the hotspot stack size check earlier. It
depends on too much other work done before that point, and the changes
would have been disruptive. The stack size check is currently done in
os::init_2().
What is needed is a check before the thread is created. That way we
can create a thread with a big enough stack to handle all needs up to
the point of the check in os::init_2(). This initial check does not
need to be the final check. It just needs to confirm that we have
enough stack to get us to the check in os::init_2().
I decided to check in java.c if the -Xss size is too small, and set it
to a larger size if it is. I hard coded this size to 32k (I'll explain
why 32k later). I suspect this is the part that will result in some
debate. If you have better suggestions let me know. If it does stay
here, then probably the 32k needs to be a #define, and maybe even an
OS porting interface, but I'm not sure where to put it.
The reason I chose 32k is because this is big enough for all platforms
to get to the stack size check in os::init_2(). It is also smaller
than the actual minimum stack size allowed on any platform. 32-bit
windows has the smallest requirement at 64k. I add some printfs to
print the minimum stack requirement, and then ran a simple JTReg test
with every JPRT supported platform to get the results.
The TooSmallStackSize.sh will run "java -version" with -Xss16k,
-Xss32k, and -XXss<minsize>, where <minsize> is the size from the
error message produced by the JVM, such as in the following:
$ java -Xss32k -version
The stack size specified is too small, Specify at least 100k
Error: Could not create the Java Virtual Machine.
Error: A fatal exception has occurred. Program will exit.
I ran this test through JPRT on all platforms, and they all pass.
One thing to point out is that Windows behaves a bit different than
the other platforms. It always rounds the stack size up to a multiple
of 64k , so even if you specify -Xss16k, you get a 64k stack. On
32-bit Windows with C1, 64k is also the minimum requirement, so there
is no error produced in this case. However, on 32-bit Windows with C2,
68k is the minimum, so an error is produced since the stack will only
be 64k. There is no bug here. It's just a bit confusing.
thanks,
Chris
