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bpf_nop_mov(var) asm macro emits nop register move: rX = rX. If 'var' is a scalar and not a fixed constant the verifier will assign ID to it. If it's later spilled the stack slot will carry that ID as well. Hence the range refining comparison "if rX < const" will update all copies including spilled slot. This macro is a temporary workaround until the verifier gets smarter. Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Andrii Nakryiko <andrii@kernel.org> Link: https://lore.kernel.org/bpf/20231226191148.48536-6-alexei.starovoitov@gmail.com