Re: [Gc] Debugging Help (X10i on OctoPOS)

Ivan Maidanski ivmai at
Wed Jan 15 04:03:23 PST 2014

Hi Andreas,

My suggestion is set data watch for vptr after it is allocated to find out which code modifies it after deallocation.


Wed, 15 Jan 2014, 10:31 +01:00 from Andreas Zwinkau <zwinkau at>:
> I could use some help/hints for debugging a GC problem.
> First some context: We use a modified X10 compiler (X10i) with a custom
> backend (libfirm). Compilation target is a custom operating system
> (OctoPOS), which in my case is running on top of Linux. We ported bdwgc
> (7.3alpha3) to use the corresponding OctoPOS API to stop the world etc.
> It works, except of the problem below.
> For a longer running application we sometimes observe some memory
> corruption. (We mostly observe a deadlock, which might be symptom of the
> same bug or another bug.)
> Using GC_DEBUG I sometimes get:
> GC_debug_free: found previously deallocated (?) object at e811eee0 in or
> near object at e811eee8(<smashed>, appr. sz = 133)
> Occasionally it crashes on the following assert in malloc.c:270, which
> apparently checks that an address from the freelist is within the
> correct heap or NULL.
>         GC_ASSERT(0 == obj_link(op)
>                   || ((word)obj_link(op)
>                         <= (word)GC_greatest_plausible_heap_addr
>                      && (word)obj_link(op)
>                         >= (word)GC_least_plausible_heap_addr));
> Using gdb, I can see that "obj_link(op)" points to a vtable, which is
> not heap allocated but static data.
> The vtable-pointer is at offset 0 in our objects. Object initialization
> follows the usual flow of "allocate;set vptr;call constructor". Hence my
> current theory: Either allocate does not remove the object from the
> freelist correctly or "set vptr" is performed on unallocated/freed memory.
> Any tips how to proceed?
> I foolishly closed the gdb session, so currently I am rerunning the app
> to trigger the assertion again. :-/
> cheers
> --
> Andreas Zwinkau
>  Karlsruhe Institute of Technology (KIT)
>  Phone:  +4972160848351
>  Email:  zwinkau at
>  Web:
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