CALLEE_PUSH_MASK
#define EBPF_SCRATCH_TO_ARM_FP(x) ((x) - 4 * hweight16(CALLEE_PUSH_MASK) - 4)
u16 reg_set = CALLEE_PUSH_MASK | 1 << ARM_IP | 1 << ARM_PC;
emit(ARM_PUSH(CALLEE_PUSH_MASK), ctx);