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April 2018

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Memory fault error
by Elliott Johnson 01 May '18

01 May '18

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@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@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@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@desktop ~ $ gcc test-sensors.c -l sensors -o test-sensors > elliott@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

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