Re: pcap segment violation

[Guy Harris <guy () alum mit edu>]

On Feb 13, 2014, at 7:21 AM, "Daniel H. Bahr" <dhbahr () gmail com> wrote:

> This keeps getting weirder...
>
> Just unplugged the SIGSEGV signal to get a stacktrace upon its
> occurrence and I've performed 3 complete cycle (that is 20000 packets)
> simulations without getting any buggy behavior.
>
> Is it at all possible that the Segment Violation signal that triggered
> the bailout was emitted from a process other than this one?

It's not possible that a SIGSEGV that causes a process to crash was emitted from a process other than the one that 
crashes - that's not how UN*Xes work.

It is not impossible that a process could send another process a SIGSEGV with a kill() call, but it's sufficiently 
unlikely that I really don't think that's what's happening.

It could be that this is a threading issue (as Michael noted, libpcap is not thread-safe; it can be run safely in a 
multi-threaded process only if

        1) you don't do pcap_compile() simultaneously in multiple threads

and

        2) you don't do operations on any particular pcap_t * simultaneously in multiple threads (you can do operations 
on one pcap_t * - except for pcap_compile() - in one thread and operations on another pcap_t * - again, except for 
pcap_compile() - in another thread, but you can't do operations on any individual pcap_t * simultaneously in more than 
one thread).

I don't know whether you can run Java inside a debugger, but, if you can, try putting the "catch SIGSEGV" code back and 
run your Java program inside a debugger (if necessary, use the right debugger commands to make sure the SIGSEGV is 
first handled by the debugger, and that the debugger stops the process so that you can get a stack trac even though the 
program is catching it).

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