[Ecls-list] Segmentation faults/detected access to ...address

[Seth Burleigh]

Just playing around the code written, I found that some lisp errors
return nil, some result in a segmentaiton fault, and some cause
cl_safe_eval to never return. 

(prin "HI") -->segmentation fault after .75 second wait time
(/ 2 0) ---> segmentation fault as above
(error "HI") -->returns nil
(subseq "a" 0 2) -->cl_safe_eval never returns (well, i only waited 10
seconds)



On Sat, 2010-03-13 at 11:56 -0600, Seth Burleigh wrote:
> Oh, forgot to mention, Im on linux running ecl 10.3.1
> 
> The error is actually thrown by cl_safe_eval, not by c_string_to_object
> (though i would think it would be thrown by c_string_to_object). Just to
> be sure, I put it right before
> cl_safe_eval(obj,(cl_object)env,Cnil) , same result.  Im guessing this
> is related to the earlier topic about SIGINT in linux not being caught
> in 10.3.1.
> 
> So i guess errors thrown by lisp code are segmentation faults if not
> caught by the lisp code or by the CL_CATCH_ALL_IF_CAUGHT block? I was
> taking a look at the (cl_object err_value) parameter of cl_safe_eval,
> and was wondering that instead of segmenting it should've simply
> returned Cnil to represent an error?
>  
> 
> 
> 
> On Sat, 2010-03-13 at 17:23 +0100, Juan Jose Garcia-Ripoll wrote:
> > I do not have time for a longer answer right now but note two things:
> > 
> > - Segmentation faults in arbitrary code can not be graciously handled
> > by ECL. Instead it just looks for the outermost CATCH_ALL statement
> > and jumps there. Since there is no such statement surrounding
> > c_string_to_object(), it just quits.
> > 
> > - puts() accesses the content of its argument. if you use puts(obj ==
> > OBJNULL) it is like using puts(1) which tries to access the memory
> > location (char*)1 causing a segmentation fault or an access violation
> > -- it depends on the OS.
> > 
> > Juanjo
> > 
> > On Sat, Mar 13, 2010 at 5:08 PM, Seth Burleigh <seth at tewebs.com>
> > wrote:
> >         So, i decided that I would try to get a c REPL going which
> >         would also
> >         catch any errors with incorrectly entered code (not go into
> >         the
> >         debugger). Cool stuff , ecl:)
> >         Anyways, I found that whenever I entered an statement which
> >         would
> >         generate an error, like the letter a, the program exits with a
> >         segmentation fault. Im not exactly sure why entering an
> >         invalid
> >         statement would generate one. I was also wondering if ecl was
> >         supposed
> >         to catch all segmentation faults which resuled from lisp code
> >         executing
> >         inside of it? According to this:
> >         http://ecls.sourceforge.net/new-manual/re41.html
> >         SIGSEGV should be caught automatically? I noticed that if i
> >         used
> >         cl_eval, everything would work, it would just go into the
> >         debugger.
> >         Also, I noticed that if i uncommented the code below it would
> >         produce a
> >         "Detected acccess to an invalid or protected memory address"
> >         and would
> >         throw me into the lisp debugger. I know this has something to
> >         do with
> >         'puts' expecting a constant char* while the statement
> >         obj==OBJNULL
> >         returns an int, but I would like to understand what exactly is
> >         causing
> >         this error.
> >         
> >         Heres the code:
> >         
> >         #include <ecl/ecl.h>
> >         #include <stdio.h>
> >         #include <string.h>
> >         
> >         int main(int argc, char **argv)  {
> >          cl_boot(argc, argv);
> >          cl_env_ptr env = ecl_process_env();
> >          while (1) {
> >            printf(">>");
> >            int nbytes = 100;
> >            char *str = (char*)malloc(nbytes);
> >            getline(&str,&nbytes,stdin);
> >            if (strcmp(str,"exit\n")==0 ) {
> >              break;
> >            }
> >         
> >            cl_object obj = c_string_to_object(str);
> >         
> >            //uncommented code below produced unprotected access error
> >            //puts(obj==OBJNULL);
> >         
> >            CL_CATCH_ALL_BEGIN(env) {
> >              cl_object evaled = cl_safe_eval(obj,(cl_object)env,Cnil);
> >              cl_pprint(1,evaled);
> >            } CL_CATCH_ALL_IF_CAUGHT {
> >              puts("ERROR");
> >            } CL_CATCH_ALL_END;
> >          }
> >          cl_shutdown();
> >         }
> >         
> >         
> >         
> >         ------------------------------------------------------------------------------
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> > 
> > 
> > -- 
> > Instituto de Física Fundamental, CSIC
> > c/ Serrano, 113b, Madrid 28006 (Spain) 
> > http://juanjose.garciaripoll.googlepages.com
> 
> 
> 
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