Re: [Chicken-hackers] [PATCH] Flow-analysis enhancement for assigned variables

[Jörg F . Wittenberger]

On Jan 30 2012, Peter Bex wrote:

> If they're not tracked, could this cause the scrutinizer to make invalid 
> type inferences and code replacements?

May I expand: Felix, assuming you have at least seen the results
of some mistaken type tag, what would be the resulting effect
to the running chicken program?


I'm asking this because I'm trying for several weeks to track
down a certain segfault.  As it happens I can observe that
one only on ARM, never on AMD64.  It occurs randomly and rare
enough to make a full call trace a no-go. (Still often enough
to be grave.)

The segfault always happens in the garbage collector either here

 scavenge:
   *x = (C_word)p2;
   p2->header = h;
   p->header = ptr_to_fptr((C_uword)p2);
   C_16_memcpy(p2->data, p->data, bytes);  <<<
 }

or at the and of "really_mark"

 p2->header = h;
 assert(!is_fptr(h));
 p->header = ptr_to_fptr((C_word)p2);
 C_17_memcpy(p2->data, p->data, bytes); <<<<
}


I guess something damages a type tag, subsequently having
the gc scan and fail on arbitrary addresses.
However I lack a theory how that would be possible.


Thanks for any hint how I could track that one down.

/Jörg