profiling

[Will Cohen]

Zdenka Safarzik wrote:
> Hello,
> 
> I want to made hardware profiling. For that purposes I need to have
> instrumented source code that has to be profiled. At every beginning and end
> of function and program loops writing to one register must be inserted. Each
> faction write different value in that register. My hardware detects access
> to that register, which function had access and time when that access was
> happen.
> 
> For source code instrumentation I want to use gcc. As gcc is very complex
> software, I hope that you can help me.
> 
> I read gecko documentation, and it seems to me that -pg or -test-coverage
> options can be used for this purpose. Can you please tell me what exactly
> these options do? Do they insert some code before compiling or before
> linking? Where is it in gcc source code? Can I easy change that code with
> writing to some register?  Is it possible to set profiling hierarchy level
> (for example: to add extra code only on "main" function instead of whole
> source)?

The -pg option puts a function call at the beginning of each function to 
mcount. The -pg option doesn't put anything at the end of the function. 
This is probably not going to be very useful for what you are interested 
in doing.

You might look at the "-finstrument-functions" option. This option puts 
a call to __cyg_profile_func_enter at the beginning of each function and 
a call to __cyg_profile_func_exit at the end of each function. The 
programmer needs to supply the instrumentation functions. It can be 
turned off with the "no_instrument_function" attribute on a 
function-by-function basis.

As far as finding how the options are implementing code, use the "-dap" 
on simple test programs to see what the RTL looks like. You can also use 
"-save-temps" to keep around the assembly language files.

The source code for gcc is available from a number of places:

http://www.gnu.org/software/gcc/mirrors.html

It may take some time to figure out how to make the changes. GCC is a 
relatively complicated program. However, the GCC Internals Manual 
available from http://www.gnu.org/software/gcc/onlinedocs/ will help.

Good luck.

-Will Cohen