c - How to automatically insert pragmas in your program

Question

I need to write a tool that can take a C code and put pragmas on top of some functions. Which compiler framework is the easiest to do such a task. Also if you can provide an example, I would really appreciate it.

Answer 1

If you want to do this reliably, you need a full C front end, and the ability to modify parsed code.

Our DMS Software Reengineering Toolkit with its C Front End can probably do what you want. DMS can parse, build ASTs, and carry out custom transformations on source text, either procedural or as a surface syntax transform.

There are some issues with macros and preprocessor directives; if you parse and retain these, it can do so in many cases but it expandis such directives where they are not "structured". Retention means you don't get a symbol table. If you expand all the directives, after parsing you can get a symbol table with the same content that a C compiler produces.

For OP's specific task, he'd like write a source to source transform something like the following:

 rule decorate_function_definition_with_pragma(fh:function_head, b: block): declaration -> declaration
       =  " fh  " ->
          " fh 
            #pragma  my_pragma 
             "
         if some_condiiton(fh);

where "my_pragma" is replace essentially by the pragma text he wants, and some_condition is custom predicate that filters matched function_headers for which the pragma should be inserted.

The pattern matches against the syntax tree, so it cannot mismatch like sed or a regex might. The secret to this is that the pattern variables reference to grammar rules in the C Front End; a pattern variable of type function_head can only match those trees that the function_head grammar rule(s) can satisfy.

One needs some trivial control logic to run this transformation just once for each encountered function definition.