Re: How can I modify the source of new,malloc

["Yann E. MORIN" <yann dot morin dot 1998 at free dot fr>]

Zvi, Mirko, All,

[Please, do not top-post...]

On Tuesday 26 June 2012 00:28:09 Mirko Banchi wrote:
> Il giorno 25/giu/2012, alle ore 23.55, Zvi Vered <veredz72@gmail.com>  
> ha scritto:
> > I have a huge application (not written by me).
> > I want to track all places where a dynamic allocation is done.
> > Is there an alternative to my way ?
> You could write your own shared object with your malloc implementation  
> and use LD_PRELOAD var.

As Mirko suggested, I'd use a loader trick to pre-load a shared lib that
overrides the malloc() and free() functions. Something like (untested!):

void* malloc( size_t size )
{
    static void* real_malloc;

    if( ! real_malloc ) {
        real_malloc = dlsym( RTLD_NEXT, "malloc" );
        if( ! real_malloc ) {
            panic_and_exit();
        }
    }
    fprintf( stderr, "Allocating %d bytes\n", size );
    return real_malloc( size );
}

Then, replacing printf with calls to backtrace(3) and backtrace_symbols_fd(3),
you can know the caller (function, offset), if you have the debug symbols in
the binaries (libs and executable), in which case you can post-process that
to find the actual  file, function and line at which the call to malloc is
made.

(Note: do not use backtrace_symbols(3), as it calls malloc! So you have
to use backtrace_symbols_fd(3)).

Then, you can write such wrappers to free(3) and so on...

Note however, that if you can recompile your application, you may want to
link with a library like DUMA or dmalloc instead of using the above trick.
  http://duma.sourceforge.net/
  http://dmalloc.com/

Which can be installed in the toolshain's sysroot by crosstool-NG ( I leave
it up to you to find in which sub-menu these libs' options live! ;-) )

Cheers,
Yann E. MORIN.

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