On 03/24/2018 02:43 AM, Alexei Starovoitov wrote:
> On 3/23/18 5:58 PM, Alexei Starovoitov wrote:
>> On 3/23/18 4:13 PM, Daniel Borkmann wrote:
>>> On 03/22/2018 04:41 PM, Alexei Starovoitov wrote:
>>>> On 3/22/18 2:43 AM, Daniel Borkmann wrote:
>>>>> On 03/21/2018 07:54 PM, Alexei Starovoitov wrote:
[...]
>>>> I picked 6 as a good compromise and used it twice in bpf_trace_run1x()
>>>> Similar thing possible for u64 arg1, u64 arg2, ...
>>>> but it will be harder to read.
>>>> Looking forward what you can come up with.
>>>
>>> Just took a quick look, so the below one would work for generating the
>>> signature and function. I did till 9 here:
>>>
>>> #define UNPACK(...) __VA_ARGS__
>>> #define REPEAT_1(FN, DL, X, ...) FN(X)
>>> #define REPEAT_2(FN, DL, X, ...) FN(X) UNPACK DL REPEAT_1(FN, DL,
>>> __VA_ARGS__)
>>> #define REPEAT_3(FN, DL, X, ...) FN(X) UNPACK DL REPEAT_2(FN, DL,
>>> __VA_ARGS__)
>>> #define REPEAT_4(FN, DL, X, ...) FN(X) UNPACK DL REPEAT_3(FN, DL,
>>> __VA_ARGS__)
>>> #define REPEAT_5(FN, DL, X, ...) FN(X) UNPACK DL REPEAT_4(FN, DL,
>>> __VA_ARGS__)
>>> #define REPEAT_6(FN, DL, X, ...) FN(X) UNPACK DL REPEAT_5(FN, DL,
>>> __VA_ARGS__)
>>> #define REPEAT_7(FN, DL, X, ...) FN(X) UNPACK DL REPEAT_6(FN, DL,
>>> __VA_ARGS__)
>>> #define REPEAT_8(FN, DL, X, ...) FN(X) UNPACK DL REPEAT_7(FN, DL,
>>> __VA_ARGS__)
>>> #define REPEAT_9(FN, DL, X, ...) FN(X) UNPACK DL REPEAT_8(FN, DL,
>>> __VA_ARGS__)
>>> #define REPEAT(X, FN, DL, ...) REPEAT_##X(FN, DL, __VA_ARGS__)
>>>
>>> #define SARG(X) u64 arg##X
>>> #define COPY(X) args[X] = arg##X
>>>
>>> #define __DL_COM (,)
>>> #define __DL_SEM (;)
>>>
>>> #define __SEQ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9
>>>
>>> #define BPF_TRACE_DECL_x(x) \
>>> void bpf_trace_run##x(struct bpf_prog *prog, \
>>> REPEAT(x, SARG, __DL_COM, __SEQ))
>>> #define BPF_TRACE_DEFN_x(x) \
>>> void bpf_trace_run##x(struct bpf_prog *prog, \
>>> REPEAT(x, SARG, __DL_COM, __SEQ)) \
>>> { \
>>> u64 args[x]; \
>>> REPEAT(x, COPY, __DL_SEM, __SEQ); \
>>> __bpf_trace_run(prog, args); \
>>> } \
>>> EXPORT_SYMBOL_GPL(bpf_trace_run##x)
>>>
>>> So doing a ...
>>>
>>> BPF_TRACE_DECL_x(5);
>>> BPF_TRACE_DEFN_x(5);
>>
>> interestingly that in addition to above defining
>> #define __REPEAT(X, FN, DL, ...) REPEAT_##X(FN, DL, __VA_ARGS__)
>> to allow recursive expansion and doing
>> __REPEAT(12, BPF_TRACE_DECL_x, __DL_SEM, __SEQ_1_12);
>> almost works...
>> I'm guessing it's hitting preprocessor internal limit on
>> number of expressions to expand.
>> It expands 1-6 nicely and 7-12 are partially expanded :)
>
> it's not the limit I'm hitting, but self referential issue.
> Exactly half gets expanded.
> I don't think there is an easy workaround other
> than duplicating the whole chain of REPEAT macro twice
> with slightly different name.
Hmm, that is kind of annoying, probably worth filing a bug on gcc, we still
won't be able to use it near term though.
Given it expands just fine from 1-6 arguments, I think Steven had a good
choice on upper limit of 6 args then (including build error with above). ;-)
Thanks,
Daniel
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