[Bioc-devel] Segfault/Valgrind/bgx

[Seth Falcon]

Hi Martin, Ernest,

Martin Morgan <mtmorgan at fhcrc.org> writes:
> Ernest,
>
> I wonder if the problem comes from writing to your C variable dirname
> in bgx.cc:243 ?
>
> At the risk of spreading mis-information, from looking at the code for
> .C, in src/main/dotcode.c:do_dotCode and RObjToCPtr, it looks like
> what happens is that 'gobbledigook' is copied to dirname[0], with
> allocation for strlen(gobbledigook)+1 space; you'll then overwite this
> with the return path, and bad things happen when the return path is
> longer than gobbledigook.

Nice catch, Martin.  I think there is a real issue there.
Overwritting the char* buffer is a problem, but you won't always see a
crash because it depends on what you overwrite.  Below are extracts
from a small test package that can be used to demonstrate this.

Now, while we are taking a look at bgx, one comment for Ernest:

   R provides nice random number and statistical distribution
   functions and you might consider using them (instead of
   bgx/src/qnorm.c, for example) -- at least when running as an R
   package.  I encourage you to consider using .Call instead of .C as
   you will have a lot more control over the inputs and what you
   return to R.


+ seth

### hello.R ###

    hello <- function(x) {
        .C("dotc_hello", x=as.character(x),
           out="HELLO1234",
           PACKAGE="hello")$out
    }

### hello.c ###

    #include <stdio.h>
    #include <string.h>
    #include <Rinternals.h>
    #include <R_ext/Rdynload.h>
    
    void dotc_hello(char **name, char **out);
    
    static const R_CMethodDef cMethods[] = {
        {"dotc_hello", (DL_FUNC)&dotc_hello, 2},
        {NULL, NULL, 0}
    };
    
    void R_init_hello(DllInfo *info)
    {
      R_registerRoutines(info, cMethods, NULL, NULL, NULL);
    }
    
    void dotc_hello(char **name, char **out)
    {
        int nprinted, navail;
        navail = strlen(out[0]);
        nprinted = sprintf(out[0], "hello, %s", name[0]);
        if (nprinted > navail) {
            Rprintf("used %d, but only %d available\n", nprinted, navail);
        }
    }



>
> Perhaps pass the return path in from R?
>
> Hope that helps,
>
> Martin
>
> Ernest Turro <ernest.turro at ic.ac.uk> writes:
>
>> Dear all,
>>
>> my package ( svn co https://hedgehog.fhcrc.org/bioconductor/trunk/ 
>> madman/Rpacks/bgx ) segfaults sometimes. I say sometimes because, for  
>> instance, on lamb1 it doesn't, and on wellington it does, on my own  
>> machine it doesn't - except if I run it through valgrind...). When I  
>> run the code as a standalone binary, there are no segfaults. Anyway,  
>> the problem according to valgrind's stack trace appears to be in  
>> libR.so - not directly in my own C code. I think it occurs when calling:
>>
>>    # bgx/R/mcmc.R:36
>>    # free allocated memory on user interrupt/end of simulation
>>    on.exit(.C("freeBGXMemory", as.integer(out.ind), as.integer 
>> (numberGenesToWatch), PACKAGE = "bgx"))
>>
>> Specifically, when calling as.integer(numberGenesToWatch).
>>
>> The relevant part of valgrind's stack trace is below. The full trace  
>> is below that. Does anyone have any ideas? I've been debugging for  
>> quite a while and I really don't know what more to do..
>>
>> Many thanks!
>
> -- 
> Martin Morgan
> Bioconductor / Computational Biology
> http://bioconductor.org
>
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>

-- 
Seth Falcon | Computational Biology | Fred Hutchinson Cancer Research Center
http://bioconductor.org