unw_resume -- resume execution in a particular stack frame

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

Programming Library                              16 August 2007                                    UNW_RESUME(3)

       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) registers. However, if execution in any of the  stack
       frames  younger  (more  deeply  nested)  than  the one identified by cp was interrupted by a signal, 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
       handling  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
       (application-binary interface).

       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.

       unw_resume -- resume execution in a particular stack frame

       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.

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

       #include <libunwind.h>

       int unw_resume(unw_cursor_t *cp);

       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.