On Thu, 1 Nov 2007 17:04:01 +0100 Ulrich Eckhardt
> 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
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.