Messages in this thread | | | From | Sven Schnelle <> | Subject | Re: [PATCH v2 7/7] tools/testing/selftests/bpf: replace open-coded 16 with TASK_COMM_LEN | Date | Mon, 29 Nov 2021 15:38:43 +0100 |
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Hi,
David Hildenbrand <david@redhat.com> writes: > On 29.11.21 15:21, Sven Schnelle wrote: >> Yafang Shao <laoar.shao@gmail.com> writes: >>> Thanks for the report and debugging! >>> Seems we should explicitly define it as signed ? >>> Could you pls. help verify it? >>> >>> diff --git a/include/linux/sched.h b/include/linux/sched.h >>> index cecd4806edc6..44d36c6af3e1 100644 >>> --- a/include/linux/sched.h >>> +++ b/include/linux/sched.h >>> @@ -278,7 +278,7 @@ struct task_group; >>> * Define the task command name length as enum, then it can be visible to >>> * BPF programs. >>> */ >>> -enum { >>> +enum SignedEnum { >>> TASK_COMM_LEN = 16, >>> }; >> >> Umm no. What you're doing here is to define the name of the enum as >> 'SignedEnum'. This doesn't change the type. I think before C++0x you >> couldn't force an enum type. > > I think there are only some "hacks" to modify the type with GCC. For > example, with "__attribute__((packed))" we can instruct GCC to use the > smallest type possible for the defined enum values.
Yes, i meant no way that the standard defines. You could force it to signed by having a negative member.
> I think with some fake entries one can eventually instruct GCC to use an > unsigned type in some cases: > > https://stackoverflow.com/questions/14635833/is-there-a-way-to-make-an-enum-unsigned-in-the-c90-standard-misra-c-2004-compl > > enum { > TASK_COMM_LEN = 16, > TASK_FORCE_UNSIGNED = 0x80000000, > }; > > Haven't tested it, though, and I'm not sure if we should really do that > ... :)
TBH, i would vote for reverting the change. defining an array size as enum feels really odd.
Regards Sven
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