What is the address of this line?

[Ingo Krabbe]

Am Dienstag, 20. Juni 2006 11:01 schrieb Andrew Haley:
> Brian Dessent writes:
>  > John Carter wrote:
>  > > So we using gcc on an embedded platform. ie. Very constrained flash &
>  > > ram.
>  > >
>  > > We also using asserts.
>  > >
>  > > Storing __LINE__ and __FILE__ is taking too much flash.
>  > >
>  > > Question: I would like to create an assert macro ....
>  > >
>  > > #define Assert( expression) do {\
>  > >    if(!(expression)) { \
>  > >      assert_occurred_at_program_counter = THE_ADDRESS_OF_THIS_LINE();
>  > > \ }
>  > > } while(0)
>  > >
>  > > So how do I write that magical function / macro
>  > > THE_ADDRESS_OF_THIS_LINE(); That returns the address / PC at that
>  > > line? Preferable in a CPU neutral fashion, otherwise for a Sparc CPU.
>  >
>  > How about something like: (see also section 5.2 of the manual)
>  >
>  > #define Assert(expression) ({ \
>  >     __label__ here; \
>  >     if (!(expression)) { \
>  >         here: assert_occurred_at_program_counter = &&here; \
>  >     } \
>  > })
>
> I also thought of
>
> void *foo ()
> {
>   return __builtin_return_address(0);
> }
>
> Andrew.

Anyway, do you really think you need this ? On an embedded platform you won't 
want the program to step out at assertions, do you ?  In the normal case, you 
only have the assertions in while you develop, on your development platform.  
Hopefully you are able to run in a simulator on your development plaftorm.

Once you compile the product for the embedded machine, you will use -DNDEBUG 
to disable the asserts.  This is the meaning and the idea behind the assert 
macro.

__LINE__ and __FILE__ aren't used to get a runtime PC of the code, but are 
debugging informations to throw out sourcecode lines at illegal behaviour.  
It seems that |__builtin_return_adress(0)| is a valid way to read PC, though.

bye ingo