On Mon, 20 Jun 2011, Russell King - ARM Linux wrote: > On Mon, Jun 20, 2011 at 06:58:45PM +0200, Arnd Bergmann wrote: > > A recent change in gcc changed the default behaviour when compiling the > > ehci driver on ARM, but the behaviour was already nondeterministic > > because the definition of the readl/writel macros on ARM relies on > > unspecified behaviour (cast to pointer with larger aligment). > > It's unspecified behaviour period. If you pass a pointer to readl/writel > which is not word aligned, what you get back is anyones guess. The pointer _is_ aligned. The problem is that it comes from the address of a structure member, which structure is marked __packed. Older GCC would see the cast to unsigned int applied to that pointer within the ARM's readl()/writel() implementation and ignore that the source of the address is marked __packed, which __packed implies an alignment of 1. REcent GCC versions would honnor the alignment of 1 and perform the unsigned int * access using byte sized loads/stores. Nicolas -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
