[Side note: for some reason, your mail had your message ordered *after* your attached diff, so replies quote the diff before the message.] On Thu, Jul 23, 2015 at 12:54:25AM +0200, Nicolai Stange wrote: > My initial intent was to rework the current integer constant expression > handling in order to allow for the recognition of constant subexpressions > built up by means of __builtin_choose_expr(). Hence the first part. > > However, since I had to touch the whole constant expression handling > code anyways, I decided to experimentally extend it to support > arithmetic constant expressions and address constants as well. Hence > the second part. > > Since the additional information on expressions obtained through the > first two parts is rather pointless without making any use of it, I > implemented part three, the checking of static storage duration > objects' initializers for constness. > This part is the reason why there is a 'RFC' tag in the subject. > It is up to you to decide whether letting sparse check for C99 > conformity is a valuable thing to have or whether being stricter than > GCC is counter-productive/completely idiotic. I think it's absolutely a valuable thing to have. It may or may not be the right *default* behavior, but having an appropriate -W option to enable it would be a good start. I've seen kernel maintainers ask people to not rely on GCC's lax enforcement of constant initializers. > sparse now finds 519 occurences of non-const initializers of static > storage duration objects, 474 of which are located in drivers/acpi > and stem from this subsystem's custom offsetof macro implemented by > means of taking pointer differences. Ideally, I'd suggest that ACPICA should add a translation from ACPI_OFFSET to offsetof as part of its Linux-izing scripts. That said, I also can't think of an obvious reason why ACPI_OFFSET *should* be considered non-constant. Perhaps there's a detail in the C99 spec that explains why what it does isn't OK, but it *seems* like it should be a compile-time constant expression. I've CCed Al Viro, who knows the C99 constant expression rules very well; Al, could you provide some clarity here? The ACPI_OFFSET macro in question expands to this: (acpi_size) (((u8 *) (void *) ((&(((struct some_struct *) 0)->fieldname)))) - ((u8 *) (void *) (((void *) (void *) 0)))) Does the -> make this non-constant? - Josh Triplett -- To unsubscribe from this list: send the line "unsubscribe linux-sparse" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
