On Mon, Feb 26, 2018 at 07:32:03AM +0100, Christophe LEROY wrote: > Le 25/02/2018 à 18:22, Mathieu Malaterre a écrit : > >-#define pfn_valid(pfn) ((pfn) >= ARCH_PFN_OFFSET && (pfn) < > >max_mapnr) > >+#define pfn_valid(pfn) \ > >+ (((pfn) - ARCH_PFN_OFFSET) < (max_mapnr - ARCH_PFN_OFFSET)) > > What will happen when ARCH_PFN_OFFSET is not nul and pfn is lower than > ARCH_PFN_OFFSET ?
It will work fine. Say you are asking for a <= x < b so (in actual integers, no overflow) that is 0 <= x-a < b-a and you also assume x-a overflows, so that we are actually comparing x-a+M < b-a with M = 2**32 or such (the maximum value in the unsigned integer type plus one). This comparison is obviously always false. (It also works if b < a btw). Segher
