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Message-ID: <20140428141420.GW26358@brightrain.aerifal.cx> Date: Mon, 28 Apr 2014 10:14:20 -0400 From: Rich Felker <dalias@...c.org> To: musl@...ts.openwall.com Subject: Re: [PATCH 3/3] stddef: Define max_align_t On Mon, Apr 28, 2014 at 03:26:45PM +0200, Szabolcs Nagy wrote: > * Jens Gustedt <jens.gustedt@...ia.fr> [2014-04-28 14:22:44 +0200]: > > Am Montag, den 28.04.2014, 12:11 +0200 schrieb Szabolcs Nagy: > > > i think i386 abi is non-conforming to the c11 alignment requirements now: > > > long long has 8 byte alignment, but in a struct/union it has only 4 > > > (this is why the attrs are needed above) > > > > > > long long x; // _Alignof(x) == 8 > > > struct {long long x;} y; // _Alignof(y.x) == 4 > > > > I don't think that it is non-conforming > > > > _Alignof of a type only tells you on what alignments the programmer > > may place objects of the corresponding type (if he deals with this > > manually) and gives no guarantee what the implementation itself choses > > under all circumstances > > > > this holds especially if a type has "extended alignment", I think > > the standard says > > "An object type imposes an alignment requirement on every object of that > type: stricter alignment can be requested using the _Alignas keyword." > > "The _Alignof operator yields the alignment requirement of its operand type." > > to me this means that all long long objects should have the same > alignment requirement and _Alignof should return this consistently > (unless _Alignas imposes further stricter alignment requirements, > but it never gets weaker) This is correct. On i386, _Alignof must both always be 4 for both long long and long double, regardless of where the operand (if it's an object rather than a type) exists. If gcc is behaving differently, this is a very bad bug in GCC that needs to be fixed on their side; I won't try to work around it. Rich
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