On 26 October 2017 at 13:10, Dan Carpenter <dan.carpenter@xxxxxxxxxx> wrote: > On Thu, Oct 26, 2017 at 12:54:20PM +0200, Rasmus Villemoes wrote: >> On 26 October 2017 at 12:48, Dan Carpenter <dan.carpenter@xxxxxxxxxx> wrote: >> > On Wed, Oct 25, 2017 at 09:25:15PM +0200, Rasmus Villemoes wrote: >> >> For some reason this spits out an enourmous amount of false positives, >> >> making this entirely useless. We hit a lot of "%lx", (long)(a - b), >> >> but I don't understand why the a-b expression (a pointer difference) >> >> passes is_ptr_type(). >> > >> > Well, it is a pointer type. If you do pointer math, you get pointer >> > results. You can't really treat subtract different from addition >> > because container_of() is a subtraction. >> >> Huh? When I subtract one pointer from another, I get an _integer_. > > No. You still get a pointer. :P That's just how type promotion works > in C. C99, 6.5.6: 9 When two pointers are subtracted, both shall point to elements of the same array object, or one past the last element of the array object; the result is the difference of the subscripts of the two array elements. The size of the result is implementation-defined, and its type (a signed integer type) is ptrdiff_t defined in the <stddef.h> header. If sparse behaves differently, it's a bug in sparse. But it may well just be me that don't quite understand the various helpers for examining type, or how types are actually implemented in sparse. I see that evaluate_ptr_sub does expr->ctype = ssize_t_ctype and return ssize_t_ctype, so something else must be going on. -- To unsubscribe from this list: send the line "unsubscribe smatch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
