libSegFault.so and gcj

Fri May 15 20:23:00 GMT 2009

Andrew Haley wrote:
>> I reason from this that the segfaults are likely stack overflows. Could
>> anyone confirm this?
>>> That's quite possible. Do you not have a debugger?
>> Clearly if it really is a stack overflow then you're not going to be
> able to call the null pointer handler. There is a way around this,
> though. If you use the -fstack-check option gcc generates a probe
> at the start of every method that writes a zero some 12kbytes below
> the stack pointer. This will give you enough stack space for the
> catch_segv handler to run.
David Daney wrote:
> Usually if you die with a SIGSEGV, it is due to stack overflow.
> Probably for one reason or another you are getting a fault during the
> NullPointerException processing which causes the signal handler to be
> reentered recursively. This goes on until the stack overflows and the
> kernel then kills the process. If you could attach a debugger to the
> process, that might shed some light on exactly what is happening.
> Assuming that it is not normal for your application to take
> NullPointerExceptions it shouldn't be too tedious.
Andrew and David, thank you for your insights and for the speed with 
which they were provided.
About the debugger; I agree it would be the easiest way to figure out 
what's going on here. Since I don't know how to reproduce the problem I 
was hoping to get some information from our devices in the field if and 
when they die of a segmentation fault.
Would it be possible -- and if so, are there any significant drawbacks 
-- to store the previous handler in INIT_SEGV and register it when 
catch_segv is entered, then re-register catch_segv on the way out? Would 
this allow the segv signal to be passed up to libSegFault.so's handler 
when it would have otherwise resulted in a recursive dead-end?
,Ben Gardiner