> From: Mikael Starvik <mikael.starvik@xxxxxxxx> > Date: Tue, 22 Sep 2015 14:19:38 +0200 > For cris it is completely valid to do that. Correct, just as it's completely valid for any system to specify an ABI that says that structures are laid out "packed" by default. > It has been an > issue before. If you for some reason really require dword > alignment there should be an align in the struct. Yep. > CC:ing the compiler guy for further comments. I have no new information. > > 22 sep 2015 kl. 14:03 skrev Kirill A. Shutemov <kirill@xxxxxxxxxxxxx>: > > Kinda. It's false positive PageTail() due low bit set in > > page->rcu_head.next. > > > > It happens (at least) due broken alignment of 'rcu' field within > > task_struct -- offsetof(struct task_struct, rcu): 773. > > > > That's looks veery broken. I would guess compiler does something horribly > > wrong. I hope it's not an ABI issue. :-/ It is an ABI issue, but I'm sure you can cope. If you need to imply something you have to provide something. If not, I'd say the term "horrible" would fit hackish assumptions of the failing code (and related code that works by happenstance). That element (the struct) needs *explicit* padding or alignment to the required multiplicity of bytes for anyone to portably be able to imply something other than "byte alignment" for the layout of it, as elements of an array, across systems. Use dummy elements or a compiler construct like __attribute__ ((__aligned__ (...))) per kernel policy or taste. I'd recommend specifying the alignment, so TRT will happen for it when it in turn is an element of an otherwise unpadded struct. (I assume all applicable allocators provide "natural" alignment of, say, sizeof (long)) or that'll be a separate issue.) brgds, H-P -- To unsubscribe from this list: send the line "unsubscribe linux-next" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
