A CIL Tutorial - Department of Computer Science - ETH Zürich

CHAPTER 7. TYPE QUALIFIERS 57
$ ciltutcc enable-tut7 -o tut7 test/tut7.c
Warning: test/tut7.c:16: color mismatch: int attribute (( blue )) int
attribute (( green ))
Which is what we expected.
7.3 Exercises
1. Modify typecheck result and colorTypesCompat to give more information when types do
not match. For example, instead of returning TypesMismatch, colorTypesCompat might return
PtrIntMismatch when t1 is a TPtr and t2 is a TInt (but the colors still match).
2. Corret the rule for function types in colorTypesCompat. Possibly add (a) new constructor(s)
to typecheck result for the case when function types do not match.
3. In combination with the above two exercises. Generalize the type checking code in colorTypesCompat.
Instead of checking the color qualiers, however, colorTypesCompat would accept a function
argument for deciding whether the set of type attributes on t1 and t2 are compatible.
4. Write the Call case in colorCheckVisitor#vinst. Extract the type of the function from
fe. Check the return type of the function against the destination of the return value (rlvo).
Check the types of the actual arguments (args) against the types of the formal parameters.
Note that there might be more actuals than formals if it is a variable argument function!
5. The attribute syntax in the warning message above could be cleaned up by inheriting
from Cil's defaultCilPrinterClass and overriding the methods for printing attributes.
7.4 Further Reading
Researchers have added ow-sensitive [3], and insensitive type-qualiers [2], type-qualier inference,
and type-qualier polymorphism [1] to languages such as C and Java [4].
In particular, the CCured [5] tool used ow-insensitive type-qualier inference to determine the
kind of fat pointer needed to check the correctness of pointer arithmetic in C, among other purposes.