Memory fault error

[Elliott Johnson]

Hello,

If this is not the correct list to report a user error, I apologize and 
will happily redirect my question where ever suitable.

I've been using cffi to make a trivial library to libsensors 
https://github.com/groeck/lm-sensors and am getting an odd memory fault 
error when referencing a string value from a groveled struct.  After 
hitting my head against a wall for a day and a half, I thought I'd ask 
in case it's a simple mistake.

Here's my information:

Running a 64 bit linux install.  My local version of the libsensors 
library is as follows:

> elliott at desktop ~ $ file /usr/lib64/libsensors.so.4.4.0
> /usr/lib64/libsensors.so.4.4.0: ELF 64-bit LSB shared object, x86-64, 
> version 1 (SYSV), dynamically linked, stripped
> elliott at desktop ~ $ sensors --version
> sensors version 3.4.0+git_83cafd29f28d463573750d897014ec7143217ae5 
> with libsensors version 3.4.0+git_83cafd29f28d463573750d897014ec7143217ae5

I'm using a fairly recent version of sbcl built from source that 
(apparently) passed all of the tests after the build:

> CL-USER> (lisp-implementation-version)
> "1.4.6.140-f8d5864d0"

My version of cffi appears to be the latest:

> CL-USER> (slot-value (asdf:find-system :cffi) 'asdf:version)
> "0.19.0"

My system uses cffi-grovel and defines the following structs:

> (cstruct sensors-bus-id "sensors_bus_id"
>          (type "type" :type :short)
>          (nr "nr" :type :short))
>
> (cstruct sensors-chip-name "sensors_chip_name"
>          (prefix "prefix" :type :string)
>          (bus "bus" :type (:struct sensors-bus-id))
>          (address "addr" :type :int)
>          (path "path" :type :string))

These are based upon the definitions in sensors/sensors.h: 
https://github.com/groeck/lm-sensors/blob/master/lib/sensors.h

After asdf loading the system, the following groveler definitions are 
created (had to dig these out of the cached build files):
> (cffi:defcstruct (sensors-bus-id :size 4)
>   (type :short :offset 0)
>   (nr :short :offset 2))
> (cl:defconstant size-of-sensors-bus-id (cffi:foreign-type-size 
> '(:struct sensors-bus-id)))
> (cffi:defcstruct (sensors-chip-name :size 24)
>   (prefix :string :offset 0)
>   (bus (:struct sensors-bus-id) :offset 8)
>   (address :int :offset 12)
>   (path :string :offset 16))
> (cl:defconstant size-of-sensors-chip-name (cffi:foreign-type-size 
> '(:struct sensors-chip-name)))
All of the above appears to be correct, so I proceed to load the library:
> (define-foreign-library libsensors
>   (:unix (:or "libsensors.so.4" "libsensors.so"))
>   (t (:default "libsensors.so")))
> (use-foreign-library libsensors)
No issues, so I define a c function from the c header file that parses a 
sensor chip name-string into a struct:

> (defcfun ("sensors_parse_chip_name" cffi-sensors-parse-chip-name) :int
>   "Parse a chip name to the internal representation.  Return 0 on 
> success, <0 on error."
>   (orig-name :string)
>   (res (:pointer (:struct sensors-chip-name))))

Which is based upon the following header function declaration:

> int sensors_parse_chip_name(const char *orig_name, sensors_chip_name 
> *res);

Then I implement a simple call to print out the parsed values (not 
including the bus):

> (defun test-sensors-parse-chip-name (string)
>   (with-foreign-object (name '(:struct sensors-chip-name))
>     (unless (= 0 (cffi-sensors-parse-chip-name string name))
>       (error "Failed to parse: ~A" string))
>     (with-foreign-slots ((prefix address path)
>                          name
>                          (:struct sensors-chip-name))
>       (format t "~%Prefix: '~A'" prefix)
>       (format t "~%Address: '~A'" address)
>       (format t "~%Path: '~A'" path))))

The above when executed gives the following output before the error:

> CL-LMSENSORS> (test-sensors-parse-chip-name "atk0110-acpi-0")
>
> Prefix: 'atk0110'
> Address: '0'

And once it tries to access the path variable, it gives the following 
error (sorry a lot rolls off the screen):

> Unhandled memory fault at #xE71B7.
>    [Condition of type SB-SYS:MEMORY-FAULT-ERROR]
>
> Restarts:
>  0: [RETRY] Retry SLIME REPL evaluation request.
>  1: [*ABORT] Return to SLIME's top level.
>  2: [ABORT] abort thread (#<THREAD "repl-thread" RUNNING {1002207F93}>)
>
> Backtrace:
>   0: (CFFI::FOREIGN-STRING-LENGTH #.(SB-SYS:INT-SAP #X000E71B7) 
> :ENCODING :UTF-8 :OFFSET 0)
>       Locals:
>         #:.DEFAULTING-TEMP. = :UTF-8
>         #:.DEFAULTING-TEMP.#1 = 0
>         #:N-SUPPLIED-0 = 1
>         POINTER = #.(SB-SYS:INT-SAP #X000E71B7)
>   1: (FOREIGN-STRING-TO-LISP #.(SB-SYS:INT-SAP #X000E71B7) :OFFSET 0 
> :COUNT NIL :MAX-CHARS 4611686018427387900 :ENCODING :UTF-8$
>       Locals:
>         #:.DEFAULTING-TEMP. = 0
>         #:.DEFAULTING-TEMP.#1 = NIL
>         #:.DEFAULTING-TEMP.#2 = 4611686018427387900
>         #:.DEFAULTING-TEMP.#3 = :UTF-8
>         ENCODING = :UTF-8
>         #:N-SUPPLIED-0 = 1
>         POINTER = #.(SB-SYS:INT-SAP #X000E71B7)
>   2: ((:METHOD TRANSLATE-FROM-FOREIGN (T CFFI::FOREIGN-STRING-TYPE)) 
> #.(SB-SYS:INT-SAP #X000E71B7) #<CFFI::FOREIGN-STRING-TYPE $
>   3: (TEST-SENSORS-PARSE-CHIP-NAME "atk0110-acpi-0") 
My guess is I'm not defining the (:struct sensors-chip-name) correctly, 
so that when sensors_parse_chip_name writes values into the struct, it 
somehow overlaps into the path string.

When looking at the source for sensors_parse_chip_name I've noticed that 
it does not set or access the path value at all.  So I decided to write 
a small c program to test the native behavior:

> elliott at desktop ~ $ cat test-sensors.c
> #include <stdio.h>
> #include <stdlib.h>
> #include "sensors/sensors.h"
>
> int main( ) {
>
>   //sensors_init( NULL );
>
>   struct sensors_chip_name name;
>
>   int return_value = sensors_parse_chip_name( "atk0110-acpi-0", &name);
>   if ( return_value != 0 ) {
>     printf( "Failed to get a good return value." );
>     exit( return_value );
>   }
>
>   printf( "Printing the prefix: '%s'\n", name.prefix );
>   printf( "Address: '%i'\n", name.addr );
>   printf( "Printing path value: '%s'\n", name.path );
>   printf ("\n exiting..." );
>
>   exit( 0 );
> }
> elliott at desktop ~ $ gcc test-sensors.c -l sensors -o test-sensors
> elliott at desktop ~ $ ./test-sensors
> Printing the prefix: 'atk0110'
> Address: '0'
> Printing path value: ''
>
>  exiting...
No problems there, so I assume that the issue is all my lack of cffi-fu 
training.  Any pointers (yes, pun intended) would be appreciated... 
sorry for such a long read, but I hope it helps to have the background.  
At the very least it helped me to frame the issue in my mind by writing 
this.

Regards,
Elliott

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://mailman.common-lisp.net/pipermail/cffi-devel/attachments/20180426/da3b8ac1/attachment.html>