How to create a plugin to instrument function calls

How to create a plugin to instrument function calls

[Paul Sery]

Hi,

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,

..
void main(...) {
  f1();
  f2();
}

as follows,

..
void main(...) {
  _mystuff('f1');
  f1();
  _mystuff('f2');
  f2();
}

I think/guess the best place for this to occur is in the assembler, like
finstrument-functions? 

I've got the basic plugin mechanics working under gcc 4.5 - i.e.,
dumb_plugin.c from testsuite - and would appreciate any suggestions about how
to proceed from here.

Regards,
Paul

Re: How to create a plugin to instrument function calls

[Ian Lance Taylor]

"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,
>
> ..
> void main(...) {
>   f1();
>   f2();
> }
>
> as follows,
>
> ..
> void main(...) {
>   _mystuff('f1');
>   f1();
>   _mystuff('f2');
>   f2();
> }
>
> 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.

Ian

Re: 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