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

[Eric Doenges <doenges@mvtec.com>]

On 27.06.2012 11:16, Eric Doenges wrote:
> On 26.06.2012 22:14, Yann E. MORIN wrote:
> 
>> 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)).

Just a short addendum: backtrace() calls malloc() internally (see bug
report from 2005 http://sourceware.org/bugzilla/show_bug.cgi?id=956), so
unfortunately you can't use it in your malloc/free wrapper.
-- 
Dr. Eric Dönges                            doenges@mvtec.com
MVTec Software GmbH | Neherstr. 1 | 81675 München  | Germany
www.mvtec.com | Tel: +49 89 457695-0 | Fax: +49 89 457695-55
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