The primary goal of this project is to define a portable and efficient
C programming interface (API) to determine the call-chain of a program.
The API additionally provides the means to manipulate the preserved
(callee-saved) state of each call-frame and to resume execution at any
point in the call-chain (non-local goto). The API supports both local
(same-process) and remote (across-process) operation. As such, the API
is useful in a number of applications. Some examples include:

o exception handling
	The libunwind API makes it trivial to implement the stack-manipulation
	aspects of exception handling. 
o debuggers
	The libunwind API makes it trivial for debuggers to generate
	the call-chain (backtrace) of the threads in a running program. 
o introspection
	It is often useful for a running thread to determine its call-chain.
	For example, this is useful to display error messages (to show how
	the error came about) and for performance monitoring/analysis. 
o efficient setjmp()
	With libunwind, it is possible to implement an extremely efficient
	version of setjmp(). Effectively, the only context that needs to be
	saved consists of the stack-pointer(s). 

WWW: http://www.nongnu.org/libunwind/