Re: Tracing objC messages

[Lucas Schnorr]

Hi David,

On 05/27/2011 05:05 PM, David Chisnall wrote:
> objc_profile_msg_enter(foo, @selector(bar), __FILE__, __LINE__);
> [foo bar];
> objc_profile_msg_exit(foo, @selector(bar), __FILE__, __LINE__);

That's nice. But how would it work? A new clang parameter for 
compilation and a dynamic linkage to a tracing library that implements 
these functions? Or the application should implement the functions by 
itself?

> You could then record timestamps along with this into a format that
> something else could parse.  I'd be happy to make this modification
> if you could define some interfaces for the profiling.

The prototypes I would implement to do this type of tracing:

void objc_trace_init (void);
void objc_trace_close (void);
void objc_trace_msg_enter (id obj,
                           SEL method,
                           const char *source_file,
                           int line);
void objc_trace_msg_exit (id obj,
                          SEL method,
                          const char *source_file,
                          int line);

I created a non-functional library with these functions:
http://dl.dropbox.com/u/1119921/objctracing-0.1.tar.gz

In a first attempt, objc_trace_init should be called as soon as the 
program starts execution (before any call to other tracing functions), 
and objc_trace_close just before it exits (to manage the trace file on 
the disk). The visualization would have the classes used by the program 
and their objects and the timeline would show the execution path of the 
single-thread program.

Afterwards, we can also try a per-thread tracing to see the execution
path of each thread, with the visualization organized in the same way. 
We would need to call objc_trace_init for each thread, but with some
parameters to identify it on the trace.

I just installed llvm/clang from the svn, so I am ready to test your
modifications to clang.

Lucas