Messages in this thread |  | | Date | Sun, 22 Jan 2023 13:42:44 +0100 | From | Jakub Jelinek <> | Subject | Re: [PATCH: 1/1] sh4: avoid spurious gcc warning |
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On Sun, Jan 22, 2023 at 12:33:41PM +0100, Michael Karcher wrote: > Am 22.01.2023 um 08:00 schrieb Randy Dunlap: > > > -#define _INTC_ARRAY(a) a, __same_type(a, NULL) ? 0 : sizeof(a)/sizeof(*a) > > > +#define _INTC_ARRAY(a) a, sizeof(a)/(_Generic((a), typeof(NULL): 0xFFFFFFFFU, default: sizeof(*a))) > > s/: / : / in 2 places. > > > > Tested-by: Randy Dunlap <rdunlap@infradead.org> # build-tested > > Thanks for your confirmation! Are you sure about the space before the colon?
No, it should be without those, see various other _Generic uses in include/linux/ All those are formatted on one line for each case, so for the above macro it would be #define _INTC_ARRAY(a) (a), sizeof(a)/(_Generic((a), \ typeof(NULL): -1, \ default: sizeof(*(a))) or so. Anyway, two comments: 1) I'd use -1 as that would be after promotion to size_t the largest size_t unlike 0xFFFFFFFFU; of course, as for the void * case a can't be an array, any value > sizeof(void*) will do 2) if *a and a is fine (i.e. argument of the macro has to be really simple or wrapped in ()s, then perhaps (a) as first operand to _Generic isn't needed either, or use (a) in the two spots (sizeof(a) is of course fine) and *(a)
> The colon in this case terminates a case descriptor for the type-level > switch construction using "_Generic". It says: "In case 'a' has the 'type of > NULL', divide by 0xFFFFFFFFU, in all other cases, divide by the size of a > single array element". It's not a colon of the ternary ?: operator, in which > case I would agree with the space before it. > > If you confirm that you want a space before the colon in this case as well, > I'm going to add it, though. > > > How far back in gcc versions does this work? > > I tested the support of _Generic on Compiler Explorer at godbolt.org. This > construction is rejected by gcc 4.8, but accepted by gcc 4.9.
Yeah, introduced in gcc 4.9, as I think kernel minimum version is 5.1, that is fine. And various headers already use _Generic.
Jakub
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