Re: Fixes segfault in beam quanting. (issue4339047)

[Han-Wen Nienhuys]

On Mon, Apr 4, 2011 at 12:22 AM, Werner LEMBERG <address@hidden> wrote:
>
>> LilyPond exposes large parts of the internal implementation through
>> the Scheme interface, and that has as a side-effect that there are
>> many ways for users to break lilypond.  This is unlikely to lead to
>> arbitrary behavior, as Guile values themselves themselves are type
>> tagged.  The worst which can happen is that a value is incorrectly
>> type-cast which leads to either a null dereference or some other
>> type assertion.
>
> Could you give a Scheme example for that, please?

Typical examples:

* scm_cdr(SCM_EOL)

This basically dereferences an (almost) null pointer.  Possibly, this
crashes neatly in debug mode (I'm not sure).  The SCM_CDR() variant
will surely crash with segmentation fault.

* unsmob_grob(x)->foo()

If x is not a grob, unsmob_grob(x) returns NULL. Boom.

>> I don't think it is productive to try to systematically plug all
>> these errors; at best, you'll replace a bunch of segmentation faults
>> with just as unhelpful assertion failures.
>
> I definitely prefer assertions to segfaults.  But maybe that's only
> me.

It does not make any difference: you'll need to start up a debugger to
figure what's going on in either case.

-- 
Han-Wen Nienhuys - address@hidden - http://www.xs4all.nl/~hanwen