segmantation fault on a 64 bit machine caused by binary compiled on a 32 bit machine
 

I compiled and run succesfully a program on a 32 bit linux machine. I tried to run the same binary on a 64 bits machine and anytime malloc is executed I got a segmentation fault. Is there a problem with libc.so.6?

I don't think. Most probably is mistake in your code, so please post relevant fragment of your code. Do not forget enclosing it with CODE tags.