On Friday, July 1, 2016 4:40:46 PM CEST Liviu Dudau wrote: > On Fri, Jul 01, 2016 at 05:17:11PM +0200, Arnd Bergmann wrote: > > On Friday, July 1, 2016 3:52:44 PM CEST Liviu Dudau wrote: > > > > > > > > > > > or do you mean we should have extra alignment in there so the > > > > private pointer has a minimum alignment higher than the > > > > alignment of struct pci_host_bridge? > > > > > > but this ^. bridge pointer arithmetic means +1 is not necessarily +sizeof(struct pci_host_bridge) > > > bytes. AFAIK that can be rounded to the nearest natural alignment for pointers on that > > > architecture. > > > > No, that's not how it works. > > Really? If struct foo takes 31 bytes, and struct foo *p = (struct foo*)64, what's p's > value after p++ ? 95? I thought the compiler is allowed to consider the structure padded so that > p++ is 96. In that example, sizeof(struct foo) is 32, so we get to the right result, for any type, this is true: (char *)((struct foo *)p + 1) == (char *)p + sizeof(struct foo); However, there is indeed a problem in the case that the private structure requires a larger alignment than struct pci_host_bridge, so adding some bytes for alignment the way that alloc_etherdev() does is probably a good idea to be on the safe side, so we could do bridge = kzalloc(ALIGN(sizeof(struct pci_host_bridge), ARCH_KMALLOC_MINALIGN) + sizeof_priv, GFP_KERNEL); priv = PTR_ALIGN(bridge + 1, ARCH_KMALLOC_MINALIGN); which will guarantee that both bridge and priv are aligned to ARCH_KMALLOC_MINALIGN and the allocation is large enough to hold both. Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
