disabled stack guard warning (ACF9, JVM 1.7, Linux)

[Tom Chiverton]

Is this (at ColdFusion start up) anything to worry about ?

Java HotSpot(TM) Server VM warning: You have loaded library /opt/fusionreactor5/instance/coldfusion9/osgi/env/runtimefw/bundle11/version0.0/bundle.jar-lib/0/libsigar-x86-linux.so which might have disabled stack guard. The VM will try to fix the stack guard now.
It's highly recommended that you fix the library with 'execstack -c <libfile>', or link it with '-z noexecstack'.

Tom

[John Hawksley]

Hi Tom,

Simple answer: no - don’t worry :-)

This is a feature in Java 7’s HotSpot compiler on Linux which tries to stop code written in C and linked into Java (the so-called Java Native Interface - JNI) from halting the whole VM if it’s written badly or maliciously.  

The code used by the JVM (called Stack Guard) inserts dummy ‘guard pages’ to detect when the C code has used too much local memory, and can raise a StackOverflowError when this happens.  In this case, the JVM can take corrective action and continue.

This problem doesn’t occur in ‘pure’ Java code because this memory is completely managed by the Java Virtual Machine.

Oracle's solution seems to be to change the library to add appropriate flags to tell the VM how to handle it, or change the way it’s linked (how it’s loaded into Java).  But this is a third-party library so we can’t easily influence these.  

The mitigating factor is that we’ve never had any reports of this library causing stack problems, so it’s a pretty safe bet this issue won’t occur.

We’ll keep an eye on the situation and update the library if they come up with a fix.

Cheer,s

-John

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John Hawksley
Senior Engineer

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