Should I be able to run java(c) in gdb?

Aleksey Shipilev shade at
Fri Dec 23 09:36:51 UTC 2016

On 12/22/2016 10:10 PM, Will Hawkins wrote:
>>> A JVM doesn't have to this but -- it could just check every object
>>> reference before trying to access an object. However for almost all
>>> programs omitting the check and catching an exception when the access
>>> fails gives better performance.
> Sorry to respond to my own email, but I was rereading this and thought
> of a related question:
> When I am compiling IcedTea, is there a way to "force" this alternate
> behavior? In other words, could I ./configure with a flag that does
> this proactive testing rather than responsive handling?

Doing the trap-based null-checks is the JIT compiler optimization, and it does
it whenever it feels fitting -- which means most of the time, unless we trapped
from a given location a lot. There is no way to force it, the compiler already
does the most it can do!

You can disable this, though, by doing -XX:-ImplicitNullChecks. But I think it
is all around better to just let VM signal handler process that SEGV first. It
will throw it further if that SEGV was legit.


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