[ltt-dev] UST Instrumenting function entries and exits

[Matthew Khouzam]

Hello world,
I just made a little program that I'm testing out and want some opinions
now that Mathieu D and Nils are not able to read their emails. ;)

This is a shared object (or code injected straight into the source) that
will allow ust calls to be hooked onto the function entries and exits.

Here is the basic code.
<code>
#include <execinfo.h>
#include <ust/marker.h>

// will add a cache for the function names later.

void __cyg_profile_func_enter (void *this_fn,
                                         void *call_site)
{
    char *funcname = backtrace_symbols(&this_fn, 1)[0];
    ust_marker(entry, "func_entry %s", funcname);
    // memory leak
}

void __cyg_profile_func_exit  (void *this_fn,
                                         void *call_site)
{
    char *funcname = backtrace_symbols(&this_fn, 1)[0];
    ust_marker(exit, "func_exit %s", funcname);
    // memory leak
}
</code>
When you make the main program, you must include in the cflags
-finstrument-code.

I would like some comments on this and to get the idea rolling to
include something similar but less ugly in ust's mainline.

The first thing I will say : backtrace_symbols does a malloc, we are
therefore doing two mallocs per function calls and no frees.
I think we do need function names and not offsets though, the user
experience is key in this feature since it is not adding a new
functionality, just making people have an easier time.
I hope that something like this would be able to make us generate UST
"sequence diagram" like viewers.

Thanks world,
Matthew