This project includes code for specific static analysis and rewriting of the
C source code of GNU R, the implementation of
the R language. The analysis focuses on VM entry points (sometimes also
known as do_ functions). A do_ function has a definition of the form
SEXP do_XXX(SEXP call, SEXP op, SEXP args, SEXP env);
where call is the AST of the call to the respective R entry point, op is
a runtime representation of it (an object of type BUILTINSXP or
SPECIALSXP), args is a single-linked list of arguments to the functions
(each argument has a name and a value), and env is an environment the R
entry point is being executed in. The objective of the static analysis in
this project is to find out how a do_ function uses its arguments; it is
known and this work confirms that most of the do_ functions use arguments
(args) and meta-arguments (call, op, env) in simple ways.
The rewriting part of this project rewrites the C source code of the do_
functions so that they accept their arguments directly on the C stack (not
in the linked list); this is only applicable to simple functions (no use of
names, fixed number of arguments, each access can be easily mapped to a
fixed argument), as discovered by the analysis. The rewriting can also
remove meta-arguments from do_ functions that do not need them.
The tools are intended to be used semi-automatically, the resulting code has to be verified manually and made prettier. The analysis works on the LLVM bitcode for the R binary (see rchk for more details on how to get this bitcode). The rewriting works on the CLANG AST level and uses the CLANG rewriter.