A CIL Tutorial - Department of Computer Science - ETH Zürich

CHAPTER 14. IMPLEMENTING A SIMPLE DSL 118
a.argName ← name of argname vi.vname;
a.argGot ← makeGlobalVar (a.argName¢"got") intType;
a.argOpt ← ¬(isMandatoryType vi.vtype);
iterCompound £implicit :false £doinit : (handle field c loc a)
£ct : vi.vtype £initl : ini;
[a]
end
| → [ ]
Now that we can extract an argument specication from an arbitrary global, we can just iterate
over all the globals to collect a list of all the arguments. The function gatherArguments performs
this iteration and returns the list of found argument specications.
let gatherArguments (f : file) : argument list =
let c = T.context for globals f in
f.globals
|> L.map (argument of global c)
|> L.concat
14.1.2 Code Generation
With the argument specications successfully gathered, we can now generate the code that actually
parses the command line. As mentioned above, we'll use the getopt long function from the C
Library. This process will involve three steps. First, we'll generate assignments to initialize the
global variables for the options to any default values given by the programmer. Second, we'll
generate a loop that calls getopt long and interprets its results. Finally, we'll generate checks to
make sure that the arguments are consistent with any assertions that the programmer gave.
Initializing the global varialbes and checking the programmer provided assertions is reletively
easy, but initializing the option strucutres and generating the loop for getopt long is more involved.
First, we'll need a few utility functions:
The function field of option gives us the CIL lval for the eld n of the i'th option structure
in the array of options based at o. We'll use it in generating Set instructions that initialize the
array of options needed for getopt long.
let field of option (o : varinfo) (ot : typ) (i : int) (n : string) : lval =
(Var o),
Index(integer i, Field(fieldinfo of name ot n, NoOffset))
The functions has arg of argument and int code of argument transform bits of the argument
specication into CIL expressions that we'll use to initialize elds of the option structures.