The /proc interfaces are available to both 32-bit and 64-bit applications. 32-bit applications can examine and control the state of other 32-bit applications. Thus, an existing 32-bit debugger can be used to debug a 32-bit application.
64-bit applications can examine and control 32-bit or 64-bit applications. However, 32-bit applications are unable to control 64-bit applications, because the 32-bit APIs do not allow the full state of 64-bit processes to be described. Thus, a 64-bit debugger is required to debug a 64-bit application.