On Thu, 1 Nov 2007 17:04:01 +0100 Ulrich Eckhardt <eckhardt@xxxxxxxxxxxxxx> wrote: > I'm by far not a MIPS expert, but I'm puzzled by the code and how it > uses signed integers for addresses. I just added some comments below, > but I'm not sure if they are valid. Thank you for any clarification! > > On Wednesday 31 October 2007, Andrew Sharp wrote: > > Since all the callers of the PHYS_TO_XKPHYS macro call with a > > constant, put the cast to LL inside the macro where it really > > should be rather than in all the callers. This makes macros like > > PHYS_TO_XKSEG_UNCACHED work without gcc whining. > > I'm not sure if this is always a compile-time constant so that you > can adorn it with a LL. However, note that this is not a cast, a cast > is at runtime. It is always a constant. > > if (sp >= (long)CKSEG0 && sp < (long)CKSEG2) > > usp = CKSEG1ADDR(sp); > > #ifdef CONFIG_64BIT > > - else if ((long long)sp >= (long long)PHYS_TO_XKPHYS(0LL, > > 0) && > > - (long long)sp < (long long)PHYS_TO_XKPHYS(8LL, 0)) > > - usp = PHYS_TO_XKPHYS((long long)K_CALG_UNCACHED, > > + else if ((long long)sp >= (long long)PHYS_TO_XKPHYS(0, 0) > > && > > + (long long)sp < (long long)PHYS_TO_XKPHYS(8, 0)) > > + usp = PHYS_TO_XKPHYS(K_CALG_UNCACHED, > > XKPHYS_TO_PHYS((long > > long)sp)); > > I'd say this code is broken in way too many aspects: > 1. A plethora of casts. PHYS_TO_XKPHYS() should return a physical > address (i.e. 32 or 64 bits unsigned integer) already, so casting its > result should not be necessary. > 2. Using a signed integer of undefined size for an address. At least > use an explicit 64 bit unsigned integer (__u64). > 3. The use of signed types makes me wonder about intended overflow > semantics. Just for the record, signed overflow in C causes undefined > behaviour, no diagnostic required, and recent GCC even assume that no > overflow occurs as an optimisation! > > > #define PHYS_TO_XKSEG_CACHED(p) > > PHYS_TO_XKPHYS(K_CALG_COH_SHAREABLE,(p)) #define > > XKPHYS_TO_PHYS(p) ((p) & TO_PHYS_MASK) #define > > PHYS_TO_XKPHYS(cm,a) (_CONST64_(0x8000000000000000) > > | \ > > - ((cm)<<59) | (a)) > > + (_CONST64_(cm)<<59) | (a)) > > This macro will always(!!!) generate a negative number, is that > intended? Well, it's an address, not a number. Does that help? The point of the macro is to convert physical addresses to a selectable type of virtual address, of which mips has several. Cheers, a
