UNW_RESUME(3)						       Programming Library						     UNW_RESUME(3)

NAME

       unw_resume -- resume execution in a particular stack frame

SYNOPSIS

       #include <libunwind.h>

       int unw_resume(unw_cursor_t *cp);

DESCRIPTION

       The  unw_resume()  routine  resumes execution at the stack frame identified by cp.  The behavior of this routine differs slightly for local
       and remote unwinding.

       For local unwinding, unw_resume() restores the machine state  and  then	directly  resumes  execution  in  the  target  stack  frame.  Thus
       unw_resume()  does not return in this case. Restoring the machine state normally involves restoring the ``preserved'' (callee-saved) regis-
       ters. However, if execution in any of the stack frames younger (more deeply nested) than the one identified by cp was interrupted by a sig-
       nal,  then unw_resume() will restore all registers as well as the signal mask. Attempting to call unw_resume() on a cursor which identifies
       the stack frame of another thread results in undefined behavior (e.g., the program may crash).

       For remote unwinding, unw_resume() installs the machine state identified by the cursor by calling the access_reg and access_fpreg  accessor
       callbacks as needed. Once that is accomplished, the resume accessor callback is invoked. The unw_resume routine then returns normally (that
       is, unlikely for local unwinding, unw_resume will always return for remote unwinding).

       Most platforms reserve some registers to pass arguments to exception handlers (e.g., IA-64 uses r15-r18 for this purpose). These  registers
       are  normally treated like ``scratch'' registers. However, if libunwind is used to set an exception argument register to a particular value
       (e.g., via unw_set_reg()), then unw_resume() will install this value as the contents of the register. In other words,  the  exception  han-
       dling arguments are installed even in cases where normally only the ``preserved'' registers are restored.

       Note  that unw_resume() does not invoke any unwind handlers (aka, ``personality routines''). If a program needs this, it will have to do so
       on its own by obtaining the unw_proc_info_t of each unwound frame and appropriately processing its  unwind  handler  and  language-specific
       data  area  (lsda).  These  steps  are generally dependent on the target-platform and are regulated by the processor-specific ABI (applica-
       tion-binary interface).

RETURN VALUE

       For local unwinding, unw_resume() does not return on success.  For remote unwinding, it returns 0 on  success.  On  failure,  the  negative
       value of one of the errors below is returned.

THREAD AND SIGNAL SAFETY

       unw_resume() is thread-safe. If cursor cp is in the local address-space, this routine is also safe to use from a signal handler.

ERRORS

       UNW_EUNSPEC
	       An unspecified error occurred.

       UNW_EBADREG
	       A register needed by unw_resume() wasn't accessible.

       UNW_EINVALIDIP
	       The instruction pointer identified by cp is not valid.

       UNW_BADFRAME
	       The stack frame identified by cp is not valid.

SEE ALSO

       libunwind(3), unw_set_reg(3), sigprocmask(2)

AUTHOR

       David Mosberger-Tang
       Email: dmosberger@gmail.com
       WWW: http://www.nongnu.org/libunwind/.

Programming Library						  16 August 2007						     UNW_RESUME(3)