_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>
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