[ECOS] Possible bug in dbg-threads-syscall.c

["Patrick Doyle" <wpd at delcomsys dot com>]

I believe that I have found a subtle bug in "dbg-threads-syscall.c", and I
would appreciate some feedback on this.

Here is the 'dbg_thread_syscall()' function.  The problem is that, on the
surface, this looks correct, but in my particular environment, where
'dbg_thread_syscall()' is called when 'dbg_syscall_ptr' is NULL, things just
don't work.

static dbg_syscall_func * dbg_syscall_ptr ;

static __inline__ int dbg_thread_syscall(
				     enum dbg_syscall_ids id)
{
  dbg_syscall_func f ; /* double indirect via */
  if (0 ==(f = *dbg_syscall_ptr)) return 0 ; /* no pointer to vector */
  if (0 == *f) return 0 ; /* vector not initialized */
  return (*f)(id,&tcall);
}

Basically, 'f' dereferences the NULL pointer, getting a non-zero value, so
that the first test passes, then the contents of address to which 'f' points
is also non-zero, so the second test passes, so the final line gets invoked
and my program disappears into never-never-land.  (Well, it would if I were
actually running it on real hardware, I actually tracked this down on the
simulator).

Anyway, here is my proposed patch, comments and feedback are definately
welcome :-)

(If this doesn't make it through the mail sanely, please send me an email
directly and I will forward the patch as an attachement -- it is very
simple).

--wpd

*** dbg-threads-syscall.c-orig	Tue Nov 27 10:01:41 2001
--- dbg-threads-syscall.c-new	Tue Nov 27 10:03:11 2001
***************
*** 82,89 ****
  				     enum dbg_syscall_ids id)
  {
    dbg_syscall_func f ; /* double indirect via */
!   if (0 ==(f = *dbg_syscall_ptr)) return 0 ; /* no pointer to vector */
!   if (0 == *f) return 0 ; /* vector not initialized */
    return (*f)(id,&tcall);
  }

--- 82,89 ----
  				     enum dbg_syscall_ids id)
  {
    dbg_syscall_func f ; /* double indirect via */
!   if (0 == dbg_syscall_ptr) return 0 ; /* no pointer to vector */
!   if (0 ==(f = *dbg_syscall_ptr)) return 0 ;  /* vector not initialized */
    return (*f)(id,&tcall);
  }