[Openmcl-devel] RDNZL in CCL: Exception occurred while executing foreign code

Gary Byers gb at clozure.com
Mon Oct 12 13:51:31 PDT 2009

'exception' in this context almost certainly means machine-level exception
(e.g., attempt to reference memory that isn't there, attempt to execute
an illegal instruction ...) and doesn't likely refer to a C++ runtime

Beyond the fact that it can show a backtrace of the lisp stack leading
up to the ff-call, CCL's kernel debugger isn't very useful for debugging
exceptions that occur in foreign (C, C++) code.  There are some (somewhat
Unix-centric) notes on using GDB at:


Native Windows debuggers may work better for debugging crashes that occur
in Windows dlls; it's been a long time since I've tried to run CCL under
something like WinDbg, and I don't remember whether there were issues or
what they were.

I suppose that there are other possibilities, but I'd be most suspicious
of the FFI/CFFI code: passing the wrong number/types of arguments to a
C[++] function can certainly lead to a memory fault or other type of
machine exception.

[It varies a bit by platform, but CCL isn't always consistent about telling
you what general kind of machine exception occurred when that exception
occurred in foreign code; on OSX, trying to FF-CALL a null pointer enters
the kernel debugger with a (very) slightly more informative message:

? (ff-call (%null-ptr) :void)
Unhandled exception 10 at 0x0, context->regs at #xb029b8f0
Exception occurred while executing foreign code
? for help
[2086] Clozure CL kernel debugger:

The "unhandled exception 10" means "bus error" (SIGBUS = 10), which is
at least a little better than saying nothing in this case.]

On Mon, 12 Oct 2009, John Miller wrote:

> All,
> On a wild hair, it seemed like it might be useful to have CCL running on my Windows XP 32-bit machine at work and use it to access Excel and Outlook using Dr. Edi Weitz's RDNZL (http://weitz.de/rdnzl/) package.  Doing this has turned out to be more difficult than I thought.  I built the FFI portion of the code using CFFI to look as close as possible to the FFI interfaces defined for the other lisps.
> For some things the FFI works.  For example:
> ? (make-type-from-name "System.Reflection.Assembly")
> #<CONTAINER System.Type #x1532E08>
> ? (import-assembly "mscorlib")
> #<CONTAINER System.Reflection.Assembly #x1532EA8>
> But if I try to get fancy:
> ? (import-types "System.Windows.Forms" "MessageBox")
> %eax = 0x00faf00c
> %ecx = 0x00000000
> %edx = 0x00000002
> %ebx = 0x79f7697c
> %esp = 0x00faf008
> %ebp = 0x00faf05c
> %esi = 0x00faf094
> %edi = 0x0040a958
> %eip = 0x7c812a6b
> %eflags = 0x00000206
> %cs = 0x001b
> %ds = 0x0023
> %ss = 0x0023
> %es = 0x0023
> %fs = 0x003b
> %gs = 0x0000
> Exception on foreign stack
> Exception occurred while executing foreign code
> ? for help
> [2068] Clozure CL kernel debugger: t
> Current Thread Context Record (tcr) = 0x5cbc20
> Control (C) stack area:  low = 0xdb0000, high = 0xfb0000
> Value (lisp) stack area: low = 0xfb0000, high = 0x0
> Exception stack pointer = 0xfaf008
> [2068] Clozure CL kernel debugger: b
> current thread: tcr = 0x5cbc20, native thread ID = 0xde4, interrupts enabled
> (#x010C0CD0) #x08D52435 : #<Function %INVOKE-STATIC-MEMBER #x08D52266> + 463
> (#x010C0D14) #x08D794D5 : #<Function INVOKE #x08D7854E> + 3975
> (#x010C0D78) #x08DD281D : #<Function IMPORT-TYPES #x08DD27CE> + 79
> (#x010C0D88) #x0839E9BD : #<Function CALL-CHECK-REGS #x0839E8C6> + 247
> (#x010C0DA4) #x083A8FE5 : #<Function TOPLEVEL-EVAL #x083A8CFE> + 743
> (#x010C0DE8) #x083AAA35 : #<Function READ-LOOP #x083AA30E> + 1831
> (#x010C0EFC) #x0839E60D : #<Function TOPLEVEL-LOOP #x0839E5C6> + 71
> (#x010C0F04) #x0834222D : #<Function (:INTERNAL (TOPLEVEL-FUNCTION (LISP-DEVELOP
> MENT-SYSTEM T))) #x083421CE> + 95
> (#x010C0F14) #x0840FDED : #<Function (:INTERNAL MAKE-MCL-LISTENER-PROCESS) #x08$
> 0FBA6> + 583
> (#x010C0F60) #x083484DD : #<Function RUN-PROCESS-INITIAL-FORM #x0834823E> + 671
> (#x010C0FA4) #x08348E7D : #<Function (:INTERNAL (%PROCESS-PRESET-INTERNAL (PROCE
> SS))) #x08348D2E> + 335
> (#x010C0FCC) #x083317A5 : #<Function (:INTERNAL THREAD-MAKE-STARTUP-FUNCTION) #x
> 0833168E> + 279
> [2068] Clozure CL kernel debugger:
> Note that I can get RDNZL to work fine using CLISP 2.48 on this same machine.
> I believe part of the problem with CCL is that Edi's C++ code will throw a C++ exception under certain conditions (though I can't figure out why the above call to %invoke-static-member is causing an exception).  Other Lisp's seem to handle this without going into the kernel debugger.  For example with Clisp 2.48 running on the same machine
> RDNZL[36]> (property "System.Reflection.Assembly" "FullName")
> *** - .NET error (System.Exception): Static property not found:
>       System.Reflection.Assembly->FullName
> Trying to call property with the same arguments in CCL bumps me into the kernel debugger.  Again, I am not 100% convinced this is the problem, but I am not sure how to interpret the output from the debugger and come up with a better hypothesis of what is happening.
> Best regards,
> John Miller
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