On 02/02/2018 11:58 AM, Martin Sebor wrote:
> The design of the attribute exclusion framework includes
> support for different exclusions applying to different
> kinds of declarations (functions, types, and variables
> or fields), but the support is incomplete -- the logic
> to consider these differences is missing. This is
> because the differences are apparently rare. However,
> as the bug below points out, they do exist.
>
> PR middle-end/84108 - incorrect -Wattributes warning for
> packed/aligned conflict on struct members, shows that while
> declaring a non-member variable aligned is enough to reduce
> the its alignment and declaring it both aligned and packed
> triggers a -Wattributes warning:
>
> int a __attribute__((packed, aligned (2))); // -Wattributes
>
> a struct member must be declared both aligned and packed in
> order to have its alignment reduced. (Declaring a member
> just aligned has no effect and doesn't cause a warning).
>
> struct S {
> int b __attribute__((packed, aligned (2)));
> int c __attribute__((aligned (2))); // no effect
> };
>
> As a result of the incomplete logic GCC 8 issues a -Wattributes
> for the declaration of b in the struct.
>
> By adding the missing logic the attached patch lets GCC avoid
> the spurious warning.
>
> I considered adding support for detecting the ineffective
> attribute aligned on the declaration of the member c at
> the same time but since that's not a regression I decided
> to defer that until GCC 9. I opened bug 84185 to track it.
>
> Tested on x86_64-linux with no regressions.
>
> Martin
>
> gcc-84108.diff
>
>
> PR middle-end/84108 - incorrect -Wattributes warning for packed/aligned
> conflict on struct members
>
> gcc/ChangeLog:
>
> PR c/84108
> * attribs.c (diag_attr_exclusions): Consider the exclusion(s)
> that correspond to the kind of a declaration.
>
> gcc/testsuite/ChangeLog:
>
> PR c/84108
> * gcc.dg/Wattributes-8.c: New test.
OK. Sorry for the wait.
Thanks.
Jeff
