The unw_set_reg() routine sets the value of register reg in the stack frame identified by cursor cp to the value passed in val.
The register numbering is target-dependent and described in separate manual pages (e.g., libunwind-ia64(3) for the IA-64 target). Furthermore, the exact set of accessible registers may depend on the type of frame that cp is referring to. For ordinary stack frames, it is normally possible to access only the preserved (``callee-saved'') registers and frame-related registers (such as the stack-pointer). However, for signal frames (see unw_is_signal_frame(3)), it is usually possible to access all registers.
Note that unw_set_reg() can only write the contents of registers whose values fit in a single word. See unw_set_fpreg(3) for a way to write registers which do not fit this constraint.
On successful completion, unw_set_reg() returns 0. Otherwise the negative value of one of the error-codes below is returned.
unw_set_reg() is thread-safe as well as safe to use from a signal handler.