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\begin{Name}{3}{unw\_init\_local}{David Mosberger-Tang}{Programming Library}{unw\_init\_local}unw\_init\_local -- initialize cursor for local unwinding
\end{Name}

\section{Synopsis}

\File{\#include $<$libunwind.h$>$}\\

\Type{int} \Func{unw\_init\_local}(\Type{unw\_cursor\_t~*}\Var{c}, \Type{unw\_context\_t~*}\Var{ctxt});\\
\Type{int} \Func{unw\_init\_local_signal}(\Type{unw\_cursor\_t~*}\Var{c}, \Type{unw\_context\_t~*}\Var{ctxt});\\

\section{Description}

The \Func{unw\_init\_local}() routine initializes the unwind cursor
pointed to by \Var{c} with the machine-state in the context structure
pointed to by \Var{ctxt}.  As such, the machine-state pointed to by
\Var{ctxt} identifies the initial stack frame at which unwinding
starts.  The machine-state is expected to be one provided by a call to
unw_getcontext; as such, the instruction pointer may point to the
instruction after the last instruction of a function, and libunwind
will back-up the instruction pointer before beginning a walk up the
call stack.  The machine-state must remain valid for the duration for
which the cursor \Var{c} is in use.

The \Func{unw\_init\_local}() routine can be used only for unwinding in
the address space of the current process (i.e., for local unwinding).
For all other cases, \Func{unw\_init\_remote}() must be used instead.
However, unwind performance may be better when using
\Func{unw\_init\_local}().  Also, \Func{unw\_init\_local}() is
available even when \Const{UNW\_LOCAL\_ONLY} has been defined before
including \File{$<$libunwind.h$>$}, whereas \Func{unw\_init\_remote}()
is not.

If the unw_context_t is known to be a signal frame (i.e., from the
third argument in a sigaction handler on linux),
\Func{unw\_init\_local\_signal}() should be used for correct
initialization on some platforms.

\section{Return Value}

On successful completion, \Func{unw\_init\_local}() returns 0.
Otherwise the negative value of one of the error-codes below is
returned.

\section{Thread and Signal Safety}

\Func{unw\_init\_local}() is thread-safe as well as safe to use from a
signal handler.

\section{Errors}

\begin{Description}
\item[\Const{UNW\_EINVAL}] \Func{unw\_init\_local}() was called in a
  version of \Prog{libunwind} which supports remote unwinding only
  (this normally happens when calling \Func{unw\_init\_local}() for a
  cross-platform version of \Prog{libunwind}).
\item[\Const{UNW\_EUNSPEC}] An unspecified error occurred.
\item[\Const{UNW\_EBADREG}] A register needed by \Func{unw\_init\_local}()
  wasn't accessible.
\end{Description}

\section{See Also}

\SeeAlso{libunwind(3)}, \SeeAlso{unw\_init\_remote(3)}

\section{Author}

\noindent
David Mosberger-Tang\\
Email: \Email{dmosberger@gmail.com}\\
WWW: \URL{http://www.nongnu.org/libunwind/}.
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