Manpages - unw_init_local.3

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_EINVAL

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).

UNW_EUNSPEC

An unspecified error occurred.

UNW_EBADREG

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

libunwind(3), unw_init_remote(3)

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