uwx(3X) 																   uwx(3X)

NAME

       uwx() - Unwind Express Library

SYNOPSIS

       [flag... ] file...  [library] ...

DESCRIPTION

       The  Unwind  Express Library is a lightweight library for unwinding a process stack on Integrity systems.  It may be used for "self-unwind-
       ing," where a thread traces back through its own stack, or for "cross-unwinding," where a debugger or other tool can examine the  stack	of
       another target thread or process.

       To  use	the  Unwind Express Library, link your application with the option on the compiler or linker command line.  All source code should
       include the header file Source code that uses the library for self-unwinding should also include the header file

       The Unwind Express Library maintains its entire state within a single unwind environment structure.  To unwind a stack, the client applica-
       tion  provides  an initial context to the unwind environment, then unwinds the stack one frame at a time.  After reaching the bottom of the
       stack, the unwind environment may be reused for a subsequent unwind operation simply by providing a new initial context, or it may be  dis-
       carded, freeing the memory it was using.

       A client application may create any number of separate unwind environments, and each one will operate independently of and completely unaf-
       fected by the others.

       The Unwind Express Library consists of a core unwind engine that can be adapted to specific environments through the use of  callback  rou-
       tines.	For self-unwinding, a set of standard callback routines are provided as part of the library.  For cross-unwinding, the client must
       supply callback routines to interface the unwind engine to the target thread or process.

   Self-Unwinding
       To prepare for self-unwinding, a client application must perform the following steps to create and initialize a new unwind environment:

	 1. Call to create a new unwind environment.  The return value is a pointer to the unwind environment.

	 2. Call to initialize the standard callback environment.  The return value is a pointer to the callback info structure.

	 3. Call to register the standard callbacks: and

       The steps above may be performed at any time in advance of performing a stack unwind.  The resulting unwind environment can  then  be  used
       repeatedly.

       To perform a stack unwind from some point in the application, the client must perform the following steps:

	 1. Call  to  provide  the  current  thread's  context as a starting point for unwinding.  The stack frame for the caller of this function
	    becomes the current frame.

	 2. Call to step back one frame in the call stack.  After each step, the new frame becomes the current frame, and the client may  call	to
	    obtain values from the reconstructed context for the new frame.  This step can be repeated until the process reaches the bottom of the
	    stack or a signal context frame.

	 3. When a signal context frame is reached, the client may call to provide a new starting point for unwinding based on the context at  the
	    point  of  interruption.   The  stack frame for the function interrupted by the signal becomes the current frame.  Subsequent calls to
	    will proceed from there.

   Cross-Unwinding
       To prepare for cross-unwinding, a client application must perform the following steps to create and initialize a new unwind environment:

	 1. Call to create a new unwind environment.  The return value is a pointer to the unwind environment.

	 2. Call to setup the unwind environment for cross unwinding.  This call also allows the client to specify the byte  order  (little-endian
	    or big-endian) of the target process.

	 3. Call to register the client-provided callback functions.  See uwx_register_callbacks(3X) for information on writing callback routines.

       The  steps  above  may be performed at any time in advance of performing a stack unwind.  The resulting unwind environment can then be used
       repeatedly.

       To perform a stack unwind, the client must perform the following steps:

	 1. Call to provide the basic initial context as a starting point for unwinding.  This initial	context  consists  of  the  values  of	ip
	    (instruction  pointer), sp (stack pointer), bsp (backing store pointer), and cfm (current frame marker).  The frame described by these
	    values becomes the current frame.  If the unwind engine needs values from additional registers in the target thread's context, it will
	    request them as needed through the callback interface.

	 2. Call  to  step back one frame in the call stack.  After each step, the new frame becomes the current frame, and the client may call to
	    obtain values from the reconstructed context for the new frame.  This step can be repeated until the process reaches the bottom of the
	    stack or a signal context frame.

	 3. When  a  signal context frame is reached, the client may call to obtain the abi and context parameters recorded in the unwind descrip-
	    tors for the frame.  This routine returns the two values in a single int as ((abi << 8) | context).  It should then call again to pro-
	    vide  a  new  starting point for unwinding based on the context at the point of interruption.  The stack frame for the function inter-
	    rupted by the signal becomes the current frame.  Subsequent calls to will proceed from there.

   Obtaining Information From the Current Frame's Context
       Registers from the current frame may be read using and

       The starting address of the current function may be obtained by calling

       Symbolic information may be obtained, if available, for the current frame's IP by calling and

ERRORS

       For the APIs that return pointer values, a NULL pointer indicates a memory allocation error; otherwise a pointer to  an	opaque	object	is
       returned.

       For other APIs, an integer status code is returned.  These codes are listed here.
       Request successfully completed.

       hit a signal context frame.

       hit bottom of stack.

       The cached information returned by the lookup-ip callback was invalid.

       The "Lookup IP" callback returned an invalid key in the result vector.

       The register id is invalid.

       The unwind information block contains an invalid descriptor.

       The unwind engine is unable to unwind from the current frame
	      because of an unsupported descriptor.

       There was an error reading a value from the memory stack.

       There was an error reading a register from the initial context.

       There was an error reading a value from the register stack backing store.

       There was an error reading the unwind information block.

       There was an error reading the unwind table.

       No module information was found for the current frame's IP.

       The "Lookup IP" callback encountered an error.

       No callback routines have been registered.

       No initial context has been supplied.

       The    env parameter is NULL.

       An attempt to allocate additional memory failed.

       No symbolic information was found.

       An unwind information block was found, but it does not describe the
	      current frame's IP.

       No unwind information block was found for the current frame's IP.

       The unwind information block is invalid -- the nesting of prologue
	      regions is not balanced.

       An unidentified error was received from the
	      uc_access(3) library.

       The unwind information block is invalid -- an undefined label is referenced.

EXAMPLES

       The following code fragment performs a stack unwind in the current thread:

LIMITATIONS

       The Unwind Express Library currently does not recognize X-format unwind descriptors.  These are not currently used by HP compilers.

AUTHOR

       The Unwind Express Library was developed by Hewlett-Packard.

SEE ALSO

       uc_access(3),  uwx_add_to_bsp(3X), uwx_find_source_info(3X), uwx_find_symbol(3X), uwx_free(3X), uwx_get_abi_context_code(3X), uwx_get_func-
       start(3X),  uwx_get_module_info(3X),  uwx_get_nat(3X),  uwx_get_reg(3X),   uwx_get_source_info(3X),   uwx_get_sym_info(3X),   uwx_init(3X),
       uwx_init_context(3X),  uwx_register_alloc_cb(3X),  uwx_register_callbacks(3X), uwx_release_symbol_cache(3X), uwx_self_do_context_frame(3X),
       uwx_self_free_info(3X),	 uwx_self_init_context(3X),   uwx_self_init_info(3X),	 uwx_set_nofr(3X),    uwx_set_remote(3X),    uwx_step(3X),
       uwx_step_inline(3X).

							      Integrity Systems Only							   uwx(3X)