A CIL Tutorial - Department of Computer Science - ETH Zürich

CHAPTER 5. INTERPRETED CONSTRUCTORS 43
Show-stopping Errors and Bugs: The function Errormsg.s ignores its argument
and throws the exception Errormsg.Error, which is only caught in
main.ml. Thus, executing E.s(E.bug ...) or E.s(E.error ...) has the eect of
stopping compilation with the given error message. If compilation could continue
despite the problemand a sensible value with the correct type could be
generatedthen E.bug and E.error could be used without E.s. Then, compilation
will continue, possibly generating further error messages.
let zeroPtr (fd : fundec) (blv : lval) : stmt list =
[i2s (Set(blv, CastE(voidPtrType, zero), locUnknown))]
The function zeroType is the entry point for NULLing out pointers found by traversing the lvalue
blv. If blv is a pointer, we NULL it out. If it is an array, we loop over the array NULLing any pointers
found in traversing the base type. If it is a struct type, we NULL any pointers found in traversing
the elds.
let rec zeroType (fd : fundec) (blv : lval) : stmt list =
match unrollType(typeOfLval blv) with
| TPtr → zeroPtr fd blv
| TArray → zeroArray fd blv
| TComp → zeroComp fd blv
| → [ ]
The function zeroComp NULLs out the pointer elds of blv assuming blv has a TComp type. If the
type of blv is a union, we just NULL out the rst pointer eld.
and zeroComp (fd : fundec) (blv : lval) : stmt list =
let ci = compinfoOfLval blv in
let sl =
ci.cfields
|> L.map (zeroField fd blv)
|> L.concat
in
if ci.cstruct then sl
else if sl ≠ [ ] then [L.hd sl]
else [ ]
The function zeroField is used by zeroComp when iterating over the elds of a compinfo. It tacks
the eld onto blv using the Cil function addOffsetLval and NULLs out any pointers in it by calling
zeroType.