[cffi-devel] How do I debug a memory fault?

[Liam Healy]

Well this is a weird one.  When I tried defcvar to define *step-rk8pd*
before, I got a memory fault.  When I re-tried it recently, it worked.
 Perhaps I didn't actually redefine it the first time when I thought I
had.

Thanks to everyone for the help.

Liam

On 10/16/07, Cyrus Harmon <ch-lisp at bobobeach.com> wrote:
> That's because you're looking at a lisp stack with gdb which doesn't
> understand the lisp stack structure. You want to call
> backtrace_from_fp with the frame pointer which should be in one of
> the registers, rsp maybe?
>
> You could try asking about debugging lisp from gdb on #lisp.
>
> good luck,
>
> Cyrus
>
> On Oct 16, 2007, at 7:00 PM, Liam Healy wrote:
>
> > Yes, I've tried that.  The problem is that I get a backtrace like so:
> > (gdb) where
> > #0  0x0000001000159475 in ?? ()
> > #1  0x0000000000000010 in ?? ()
> > #2  0x0000000000001000 in ?? ()
> > #3  0x000000100015afa1 in ?? ()
> > #4  0x000000100015b09f in ?? ()
> > #5  0x0000000040000017 in ?? ()
> > #6  0x000000100015afa1 in ?? ()
> > #7  0x00000010004683a3 in ?? ()
> > #8  0x00002b8a3182f800 in ?? ()
> > #9  0x000000004000004f in ?? ()
> > #10 0x0000001002f32767 in ?? ()
> > #11 0x0000000040000017 in ?? ()
> > #12 0x000000100015afa1 in ?? ()
> > #13 0x000000004000004f in ?? ()
> > #14 0x0000000000000000 in ?? ()
> >
> > Not very informative.  I've even tried to recompile SBCL with symbols
> > not stripped,  but it doesn't help.
> >
> > Liam
> >
> >
> >
> > On 10/9/07, Daniel Herring <dherring at tentpost.com> wrote:
> >> Have you tried attaching gdb to the lisp process?
> >> I spot most of my errors by setting breakpoints and looking at the
> >> actual
> >> function call.
> >>
> >> The session would look something like
> >> SHELL> ps ax | grep lisp  (or sbcl or clisp or...)
> >> SHELL> gdb lisp 1234 (where 1234 is the process ID)
> >> GDB> print gsl_odeiv_step_rk8pd
> >> (this should be the same value you see in lisp)
> >> GDB> break gsl_odeiv_step_alloc
> >> GDB> continue
> >> CL> (call-bad-cffi)
> >> (gdb stops lisp when it calls the function)
> >> GDB> print gsl_odeiv_step_type
> >> (this pointer's value should be the same as before)
> >> GDB> detach
> >> GDB> quit
> >>
> >> - Daniel
> >>
> >> On Tue, 9 Oct 2007, Liam Healy wrote:
> >>
> >>> James,
> >>>
> >>> I tried both
> >>>
> >>> (defvar *step-rk8pd* (cffi:foreign-symbol-pointer
> >>> "gsl_odeiv_step_rk8pd"))
> >>>
> >>> and
> >>>
> >>> (cffi:defcvar ("gsl_odeiv_step_rk8pd" *step-
> >>> rk8pd*) :pointer :read-only t)
> >>>
> >>> I'm not clear on what the difference is, but they both give a memory
> >>> fault.
> >>>
> >>> Liam
> >>>
> >>>
> >>>
> >>> On 10/9/07, James Bielman <jamesjb at haytonsystems.com> wrote:
> >>>> On Sun, 2007-10-07 at 13:16 -0400, Liam Healy wrote:
> >>>>> I am using CFFI in SBCL on Debian GNU/Linux etch (amd64).  I
> >>>>> have had
> >>>>> a great deal of success interfacing to the GNU scientific library
> >>>>> (GSL).  Usually, when I get a "memory fault" I quickly can see my
> >>>>> mistake in defining the interface, and once fixed, the error goes
> >>>>> away.
> >>>>>
> >>>>> I can't figure this one out however.  The interface is:
> >>>>>   gsl_odeiv_step * gsl_odeiv_step_alloc (const
> >>>>> gsl_odeiv_step_type *
> >>>>> T, size_t dim)
> >>>>> I attempt to call this with a predefined pointer,
> >>>>>   (describe *step-rk8pd*)
> >>>>>   #.(SB-SYS:INT-SAP #X2B31DAEB0328) is a SB-SYS:SYSTEM-AREA-
> >>>>> POINTER.
> >>>>> and I get a memory fault.  What is the best way to debug this?
> >>>>
> >>>> Hi Liam,
> >>>>
> >>>> You don't show how you are defining *STEP-RK8PD* here, but I am
> >>>> wondering if what you actually have is the address of that
> >>>> variable.
> >>>>
> >>>> Are you defining this with DEFCVAR?
> >>>>
> >>>> James
> >>>>
> >>>>
> >>>>
> >>> _______________________________________________
> >>> cffi-devel mailing list
> >>> cffi-devel at common-lisp.net
> >>> http://common-lisp.net/cgi-bin/mailman/listinfo/cffi-devel
> >>>
> >> _______________________________________________
> >> cffi-devel mailing list
> >> cffi-devel at common-lisp.net
> >> http://common-lisp.net/cgi-bin/mailman/listinfo/cffi-devel
> >>
> > _______________________________________________
> > cffi-devel mailing list
> > cffi-devel at common-lisp.net
> > http://common-lisp.net/cgi-bin/mailman/listinfo/cffi-devel
>
>