[ clisp-Bugs-1112118 ] handle_fault error2 sigsegv error resurfaced

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Bugs item #1112118, was opened at 2005-01-29 11:15
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https://sourceforge.net/tracker/?func=detail&atid=101355&aid=1112118&group_id=1355

Category: ffi
Group: segfault
Status: Open
Resolution: None
Priority: 5
Submitted By: John Small (jwebsmall)
Assigned to: Jörg Höhle (hoehle)
Summary: handle_fault error2  sigsegv error resurfaced

Initial Comment:
I'm running CLisp 2.33.1 on win32 from binaries
download from
clisp.org.

I've written a simple set of dbi/dbd  packages for odbc and
mysql.   The odbc driver works fine.  The mysql direct
driver I ported to CLisp FFI from a c wrapper I wrote
interfacing with the mysql client api.  This c wrapper
in c apps works fine also.

The CLisp FFI mysql direct driver works okay on some
simple data result sets.  But on more complex result
sets just calling mysql_fetch_row signals:

      handle_fault error2 sigsergv error

with the customary address of the violation.

Please note that the call to mysql_fetch_row simply
returns a char ** which is an array of char * pointers
to the field/column data strings.  CLisp crashes in this
call.

Since I'm new to CL and this is my first
CL program (although I have developed in Scheme)
I figure I might be doing something wrong and
that segment faults might actually be trigged
by something I'm doing wrong.

Essentially the code looks like this:

#|  from the mysql.h file

MYSQL_ROW  STDCALL mysql_fetch_row(MYSQL_RES *result);

Where MYSQL_ROW is defined as char **
and MYSQL_RES is a pointer to a mysql handle
that I never introspect.

The pseudo code below works fine on simple data sets
only have simple values and a few columns.  As soon
as string data and returned NULL's are involved it
crashes.  But it will crash even when no NULL's are
involved!

|#

(FFI:DEF-CALL-OUT      mysql_fetch_row
  (:library                    "libmySQL.dll")
  (:language                :stdc)
  (:name                     "mysql_fetch_row")
  (:arguments
    (res                        ffi:c-pointer))
  (:return-type              (ffi:c-array-ptr 
ffi:c-string)))

...

;; result is okay value from before and can
;; be used in functions to retrieve number of fields etc.

(let ((row (mysql_fetch_row result)) ;; crashes here!
      (fields nil))
  (if row
      (do ((i 0 (1+ i)))
        ((>= i num-fields) (setf fields (nreverse fields)))
        (push (aref row i) fields)))

;;  aref crashes on null values which is a separate problem

Thanks for any help.  If you need my complete package
sources I can send those also.


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