[Ecls-list] Possible bug: segfault when setting slots in CFFI

Andrew Lyon orthecreedence at gmail.com
Sat Jun 21 17:09:14 UTC 2014

Your notes on debugging should help me out significantly. I had forgotten
about the :c-file and other switches. I'll also read up on the UFFI
interface and see if I can find where the bug lies. Thanks for the tips!

On Fri, Jun 20, 2014 at 5:47 PM, Waldek Hebisch <hebisch at math.uni.wroc.pl>

> Andrew Lyon wrote:
> >
> > Hey everyone (again). Since my last email, I found what appears to be a
> > weird CFFI/ECL bug. This was the cause of the problem I reported earlier
> > today. It seems like the code in the function runs fine, but on return it
> > barfs a segfault:
> >
> > https://gist.github.com/orthecreedence/15dea89a0a7d591bba51
> >
> > Note that I ended up working around this problem using ffi:c-inline to
> set
> > the values in the struct manually, but I consider this an ugly fix that
> I'd
> > rather not have there.
> >
> > Any ideas on what's wrong? Thanks!
> Probably not the cause of your problem, but AFAICS you have wrong types
> in foreign calls: 'memset' needs 'size_t' as third (last) argument
> and you pass ':unsigned-char'.  Similarly 'htons' has unsigned short
> as argument. 'htonl' need 32-bit unsigned integer as argument
> and returns 32-bit unsigned integer.  On Windows 'long' gives
> right size, but on other systems long may be too big (long typically
> has 64-bits on non-Windows 64-bit systems).
> My method to debug such problem is to put Lisp source in a file and
> use :c-file :h-file :data-file keyword arguments to 'compile-file'
> to capture resulting C code.  Then I look at C code to check if
> it is right -- that should localize the problem to specific plase.
> Once you know problem spot you may trace what 'cffi:with-foreign-slots'
> is doing and what wnet wrong.
> Note: native ecl FFI is UFFI and it allows you to assign to foreign
> data.  So you may manually assign slots at UFFI level.  I did not
> use CFFI but probably its constructs are translated (macro-expanded)
> to native (UFFI for ecl) constructs.  In such case looking at UFFI
> translation you should be able to determine if ecl has bug in its
> implementation of UFFI or bug is in CFFI.
> --
>                               Waldek Hebisch
> hebisch at math.uni.wroc.pl
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