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.
> 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?
Uli
- slightly puzzled -
--
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