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_UC_MACHINE_FP() is a helper macro to extract from mcontext a frame pointer. Don't rely on this interface as a compiler might strip frame pointer or optimize it making this interface unreliable. For hppa assume a small frame context, for larger frames FP might be located in a different register (4 instead of 3). For ia64 there is no strict frame pointer, and registers might rotate. Reuse 79 following: ./gcc/config/ia64/ia64.h:#define HARD_FRAME_POINTER_REGNUM LOC_REG (79) Once ia64 will mature, this should be revisited. A macro can encapsulate a real function for extracting Frame Pointer on more complex CPUs / ABIs. For the remaining CPUs, reuse standard register as defined in appropriate ABI. The direct users of this macro are LLVM and GCC with Sanitizers. Proposed on tech-userlevel@. Sponsored by <The NetBSD Foundation>