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clinux-kernelmacrosbpfebpf

eBPF: understand two macros in verifier code

I'm looking in the ebpf verifier code, and I can't get my head around the following macros:

#define offsetof(TYPE, MEMBER)  ((size_t)&((TYPE *)0)->MEMBER)
#define offsetofend(TYPE, MEMBER) \
    (offsetof(TYPE, MEMBER) + sizeof(((TYPE *)0)->MEMBER))

<...>

#define bpf_ctx_range(TYPE, MEMBER)                     \
    offsetof(TYPE, MEMBER) ... offsetofend(TYPE, MEMBER) - 1
#define bpf_ctx_range_till(TYPE, MEMBER1, MEMBER2)              \
    offsetof(TYPE, MEMBER1) ... offsetofend(TYPE, MEMBER2) - 1

I understand offsetof and offsetofend macros, but what is ... meaning?

Thanks.

Solution

  • Check out how it's used in filter.c:

        case bpf_ctx_range(struct __sk_buff, data):

    This is GCC's case range extension (it's also supported by clang). With it, a single case statement can match on a range of values, like case 0 ... 5:. There's more information here:

    https://gcc.gnu.org/onlinedocs/gcc/Case-Ranges.html