trouble with FFI primitives

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trouble with FFI primitives

Michael Haupt-3
Hi,

we're experiencing something strange with Squeak and FFI on Linux.
Could someone please give us some insight on the problem at hand, and
how to solve it?

/usr/lib/squeak/3.11.3-2135/so.SqueakFFIPrims: cannot enable
executable stack as shared object requires: Permission denied

We have code compiled with gcc 4.4.2. We expose one method that works
perfectly well when called from C - but we need to call it from
Squeak. The code is pasted below.

Best,

Michael

-----header file-----
#include <krb5.h>
#include <stdio.h>
#include <strings.h>
#include <stdlib.h>
static int Krb5_get_init_creds_password_proxy(char* userString, int
userSize, char* pwString, int pwSize);
static char Krb5_get_init_creds_password(char* user, char* pass);
-----end of header-----

-----C file-----
#include <krb5_simple_auth.h>

struct krb5_object {
  krb5_context ctx;
  krb5_creds creds;
  krb5_principal princ;
};

/*
 * call-seq:
 *   new
 *
 * Create a new Krb5Auth::Krb5 object.  This must be called before any
other methods are called.  Returns true on success, raises
Krb5Auth::Krb5::Exception on failure.
 */
static struct krb5_object * Krb5_new()
{
  struct krb5_object *kerb;
  krb5_error_code krbret;

  kerb = (struct krb5_object *)malloc(sizeof(struct krb5_object));
  if (kerb == NULL) /* fail */;

  memset(kerb, 0, sizeof(struct krb5_object));

  krbret = krb5_init_context(&kerb->ctx);
 if (krbret) /* fail */;

  return kerb;
}

/*
 * call-seq:
 *   get_init_creds_password(username, password)
 *
 * Call krb5_get_init_creds_password() to get credentials based on a
username and password.  Returns true on success, raises
Krb5Auth::Krb5::Exception on failure.
 */
static char Krb5_get_init_creds_password(char* user, char* pass)
{

  struct krb5_object *kerb = Krb5_new();
  krb5_error_code krbret;

  krbret = krb5_parse_name(kerb->ctx, user, &kerb->princ);
  if (krbret) {
    //fail
  }

  krbret = krb5_get_init_creds_password(kerb->ctx, &kerb->creds, kerb->princ,
                                        pass, 0, NULL, 0,NULL, NULL);
  if (krbret)
     return 0;
  else
     return 1;
}

static int Krb5_get_init_creds_password_proxy(char* userString, int
userSize, char* pwString, int pwSize) {
   char* user = (char*)calloc(userSize+1, sizeof(char));
   char* password = (char*)calloc(pwSize+1, sizeof(char));

   strncpy(user, userString, userSize);
   user[userSize] = '\0';
   strncpy(password, pwString, pwSize);
   user[pwSize] = '\0';

   return (int)Krb5_get_init_creds_password(user, password);
}

int main(int argc, char** argv) {
   if (argc < 3) return 1;

   printf("User %s with %s: %d\n", argv[1], argv[2],
(int)Krb5_get_init_creds_password(argv[1], argv[2]));
   return 0;
}
-----end of C file-----

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Re: [Vm-dev] trouble with FFI primitives

Bert Freudenberg

On 23.10.2009, at 14:41, Michael Haupt wrote:

>
> Hi,
>
> we're experiencing something strange with Squeak and FFI on Linux.
> Could someone please give us some insight on the problem at hand, and
> how to solve it?
>
> /usr/lib/squeak/3.11.3-2135/so.SqueakFFIPrims: cannot enable
> executable stack as shared object requires: Permission denied

Try

echo 0 > /proc/sys/kernel/exec-shield

If it works then, you need to figure out which compiler flags to use  
to allow the stack to be executable. I'd expect compiling the VM (or  
just the FFI module) on the same system as your library would make it  
work. For enlightenment (or frustration, depending on your POV) read  
this:

http://people.redhat.com/drepper/nonselsec.pdf

- Bert -