bug#13074: VM Segfaults with Bad `Call' Instruction

[Noah Lavine <noah.b.lavine@gmail.com>]

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On Tue, Dec 11, 2012 at 4:42 AM, Ludovic Courtès <ludo@gnu.org> wrote:
>
> The VM does full error checking.  But there’s a difference between
> checking whether an object has the expected type, and checking whether
> an object is a well-formed ‘SCM’ object (and NULL is not a valid ‘SCM’
> object.)
>
> Guile never does the latter, and as a rule of thumb I would keep things
> this way.
>

Okay.


> The brave hacker working on a compiler can easily figure out what how to
> debug all sorts of crazy things.  :-)
>

Yes, "easily". :-)


> So I’m closing it for now.
>
> Thanks,
> Ludo’.
>
> PS: It’s still unclear to me how you ended up forging an invalid SCM
>     object.  I think you either have to generate invalid bytecode, or to
>     use (pointer->scm %null-pointer), or variants thereof.
>

I loaded a procedure on the stack, used the new-frame instruction, and then
the call instruction. When I switched the order of the first two things,
the problem went away. I must have been using uninitialized stack space.

Noah

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