I have a patch for this, but I'm not sure of the right way to offer it.
I'm attaching a file that I hope gets the point across. This enters all
the label names within a function body into alphaTable at the beginning
of processing a function definition.
Aside from fixing the problem I mentioned, this also has the benefit of
having CIL raise an error if there are duplicate label names, rather
than silently allowing them to go through.
Comments are welcome.
-Elnatan
On Mon, 2009-08-03 at 17:43 -0400, Elnatan Reisner wrote:
> CIL doesn't check the uniqueness of label names it uses when unfolding
> short-circuiting boolean operators. This can lead to problems if you
> already have a label named "_L" in your program. I've attached a tiny
> example that gets converted from a stupid but harmless program into a an
> infinite loop because of this.
>
> I haven't yet managed to figure out all of the pieces involved in CIL's
> handling of labels, so if someone can suggest a fix for this, I'd
> appreciate it.
>
> On a related (but not functionally problematic) note, is there a reason
> inserted gotos have their location marked as unknown, rather than as
> being the same as that of expression from which they originate? More
> specifically, Cabs2cil.compileCondExp creates gotos with the line
>
> (gotoChunk lab lu, consLabel lab sf !currentLoc false)
>
> where "lu" is locUnknown. Is there a reason this shouldn't be "!
> currentLoc" instead?
>
> -Elnatan
--- cabs2cil.ml~ 2009-04-24 14:50:33.000000000 -0400
+++ cabs2cil.ml 2009-08-05 17:41:06.520503882 -0400
@@ -1089,6 +1089,17 @@
with Not_found ->
l
+class gatherLabelsClass : V.cabsVisitor = object (self)
+ inherit V.nopCabsVisitor as super
+
+ method vstmt s = match s with
+ | A.LABEL (l,_,loc) ->
+ currentLoc := convLoc loc;
+ let newname, oldloc = newAlphaName false "label" l in
+ if newname <> l then E.s (error "Duplicate label name %s (previous use of this label is at %a)" l d_loc oldloc);
+ V.DoChildren
+ | _ -> V.DoChildren
+end
(** ALLOCA ***)
let allocaFun () =
@@ -5522,6 +5533,10 @@
(* Setup the environment. Add the formals to the locals. Maybe
* they need alpha-conv *)
enterScope (); (* Start the scope *)
+
+ (* Enter all the function's labels into the local scope *)
+ ignore (V.visitCabsBlock (new gatherLabelsClass) body);
+ currentLoc := funloc; (* gatherLabelsClass#vstmt changes currentLoc, so reset it here *)
IH.clear varSizeArrays;
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