question about _sig_on _sig_off in cython code

[luisfe]

Hi,

I have found an unhandled SIGFPE in number_field_element_quadratic as
explained in ticket http://trac.sagemath.org/sage_trac/ticket/9357

Basically, sage does not check if a quadratic algebraic number is zero
when trying to invert it.

I added a trivial patch that checks if the zero element is being
inverted to rise a ZeroDivisionError. However, the error message
before the crash suggests that the compiled code is not properly
wrapped with _sig_on _sig_off.

In this example even if one adds this wrapper the zero check is
advisable, since _sing_on would rise a RuntimeError instead a
ZeroDivisionError, so it seems that the zero check is enough in this
case. On the other hand would the _sig_on stuff made the code more
robust? What is the way to proceed in this cases?

Thanks,

Luis

[Robert Bradshaw]

You did the right thing. The _sig_on and _sig_off are more about being
able to trap signals such as interrupts (so that control-C works).

- Robert

[David Kirkby]

Is there any quick way of finding code which might not be wrapped
properly with sig_on and sig_off? I think the seg fault I get at
startup indicates that as a possible problem. (Not sure. Forget error
message and can't check now. Batteries just about to die in laptop)