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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) 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).


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)

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