How to create a plugin to instrument function calls?

[Paul Sery]

Ian Lance Taylor <iant@google.com> said:

> "Paul Sery" <pgsery@swcp.com> writes:
> 
> > I want to create a plugin that inserts custom code before function calls. The
> > plugin would mimic the way fprofile-arcs instruments function calls, but not
> > other structures. For instance, I'd like to modify the following code,
> > ...
> > I think/guess the best place for this to occur is in the assembler, like
> > finstrument-functions? 
> 
> The assembler is an OK place to hack things which change the function
> prologue or epilogue.  It sounds like you want to change the actual body
> of the function, which is quite different.  I would suggest working at
> the GIMPLE level instead, and modifying function calls there.
> 
Ok, I'll go that route. Can I use the single function like the
finstrument-functions option uses?
  ...
  profile_function_entry_libfunc
    = init_one_libfunc ("__cyg_profile_func_enter");
  --->
  profile_function_entry_libfunc
    = init_one_libfunc ("__myfn");

or perhaps I should mimic the way the gcov option works?
   ...
   = build_function_type_list (void_type_node,...
   = build_fn_decl ("__gcov_interval_profiler",
   ...

Thanks,
Paul