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SubjectRe: [00/02] add BUILD_BUG_DECL assertion (for 3.4??)
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On Sun, 2012-04-08 at 16:38 -0600, Jim Cromie wrote:

> this patch (0001) adds new bug.h macro, BUILD_BUG_DECL(name, cond),
> which unlike other *BUG* assertions is usable at file scope. Its
> primary purpose is to enforce identical sizes of 2 separate arrays,
> which but for considerations of packing/padding/section, would be
> together in a struct.
>
> const char const *names[] = { "bart", "lisa", "homer", "marge" };
> int a[] = {1,2,3,4};
> int b[] = {1,2,3,5};
> long d[] = {1,2};
>
> BUILD_BUG_DECL(foo, ARRAY_SIZE(a) != ARRAY_SIZE(b));
> BUILD_BUG_DECL(buz, sizeof(a) != sizeof(b)); // good
> BUILD_BUG_DECL(a, sizeof(a) != sizeof(d)); // ok on x32, error x64
> BUILD_BUG_DECL(b, ARRAY_SIZE(a) != ARRAY_SIZE(names)); // good
>
> macro expands as:
> static __attribute__ ((__section__(".init.data"))) struct {
> int BUILD_BUG_DECL_buz[1 - 2*!!(sizeof(a) != sizeof(b))];
> } BUILD_BUG_DECL_buz[0] __attribute__((unused));
>

If possible, it might be better to wrap the
declarations themselves in a macro that ensures
the sizes are the same.

Something like:

declare_same_size_arrays(
typeof array1[] = {...},
typeof array2[] = {...}
);



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