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RE: [CIL users] Implicit Index(0,NoOffset)
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From: Matt H. <ma...@cs...> - 2006-03-06 21:40:00
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Hi Nathan,
Index offsets should only appear on arrays, not pointers, so ptr should
never have an Index offset. Or am I missing something?
One place where there is an implicit Index(0, NoOffset) is in the line ptr
= x.blocks.
Cil represents this as StartOf(x.blocks), which means the same thing as
AddrOf(x.blocks[0]).
-- Matt
> -----Original Message-----
> From: cil...@li...
> [mailto:cil...@li...] On Behalf Of
> Nathan Cooprider
> Sent: Monday, March 06, 2006 12:53 PM
> To: cil...@li...
> Subject: [CIL users] Implicit Index(0,NoOffset)
>
> I have been using the addOffsetLval function and I believe I
> may have found a bug. However, I also might just be doing
> something wrong. In code like the following example, there
> seems to be an implicit
> Index(zero,NoOffset) at the end of an Lval. This breaks things:
>
> struct block_struct {
> int data;
> int priority;
> };
> struct problem {
> struct block_struct blocks[10];
> int something_else;
> };
>
> int main () {
> struct problem x;
> struct block_struct * ptr = x.blocks;
> //if(ptr[0].priority ==0)
> if (ptr->priority == 0)
> return 0;
> else
> return 1;
> }
>
> I put a comment above the ptr variable conditional that shows
> where the implicit index is. I believe that having this
> implicitly there is somewhat inconsistent, but it might be
> unavoidable.
>
> I changed addOffsetLval to deal with this (code below).
> However, if this really is a problem (and not just me
> misunderstanding something) then a more general solution is
> probably needed.
>
> Nathan
>
> (* in cil.ml You also have to lift isArrayType to be above
> this fcn *) let addOffsetLval toadd (b, off) : lval =
> match toadd with
> Field _ when (isArrayType (typeOfLval (b,off))) ->
> b, addOffset toadd (addOffset (Index(zero,NoOffset)) off)
> | _ -> b, addOffset toadd off
>
>
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