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UNW_INIT_LOCAL(3libunwind) Programming Library UNW_INIT_LOCAL(3libunwind)


unw_init_local -- initialize cursor for local unwinding


#include <libunwind.h>

int unw_init_local(unw_cursor_t *c, unw_context_t *ctxt);
int unw_init_local2(unw_cursor_t *c, unw_context_t *ctxt, int flag);


The unw_init_local() routine initializes the unwind cursor pointed to by c with the machine state in the context structure pointed to by ctxt. As such, the machine state pointed to by 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 c is in use.

The 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, unw_init_remote() must be used instead. However, unwind performance may be better when using unw_init_local(). Also, unw_init_local() is available even when UNW_LOCAL_ONLY has been defined before including <libunwind.h>, whereas 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), unw_init_local2() should be used for correct initialization on some platforms, passing the UNW_INIT_SIGNAL_FRAME flag.


On successful completion, unw_init_local() returns 0. Otherwise the negative value of one of the error codes below is returned.


unw_init_local() is thread safe as well as safe to use from a signal handler.


unw_init_local() was called in a version of libunwind which supports remote unwinding only (this normally happens when calling unw_init_local() for a cross-platform version of libunwind).

An unspecified error occurred.

A register needed by unw_init_local() wasn't accessible.


libunwind(3libunwind), unw_init_remote(3libunwind)


David Mosberger-Tang

29 August 2023 Programming Library