On 31.10.2023 11:03, Nicola Vetrini wrote: > On 2023-10-31 09:28, Nicola Vetrini wrote: >> On 2023-10-31 08:43, Jan Beulich wrote: >>> On 30.10.2023 23:44, Stefano Stabellini wrote: >>>> On Mon, 30 Oct 2023, Jan Beulich wrote: >>>>> On 27.10.2023 15:34, Nicola Vetrini wrote: >>>>>> --- a/xen/include/xen/macros.h >>>>>> +++ b/xen/include/xen/macros.h >>>>>> @@ -8,8 +8,14 @@ >>>>>> #define DIV_ROUND(n, d) (((n) + (d) / 2) / (d)) >>>>>> #define DIV_ROUND_UP(n, d) (((n) + (d) - 1) / (d)) >>>>>> >>>>>> -#define MASK_EXTR(v, m) (((v) & (m)) / ((m) & -(m))) >>>>>> -#define MASK_INSR(v, m) (((v) * ((m) & -(m))) & (m)) >>>>>> +/* >>>>>> + * Given an unsigned integer argument, expands to a mask where >>>>>> just the least >>>>>> + * significant nonzero bit of the argument is set, or 0 if no bits >>>>>> are set. >>>>>> + */ >>>>>> +#define ISOLATE_LOW_BIT(x) ((x) & -(x)) >>>>> >>>>> Not even considering future Misra changes (which aiui may require >>>>> that >>>>> anyway), this generalization of the macro imo demands that its >>>>> argument >>>>> now be evaluated only once. >>>> >>>> Fur sure that would be an improvement, but I don't see a trivial way >>>> to >>>> do it and this issue is also present today before the patch. >>> >>> This was an issue here for MASK_EXTR() and MASK_INSR(), yes, but the >>> new >>> macro has wider use, and there was no issue elsewhere so far. >>> >>>> I think it >>>> would be better to avoid scope-creeping this patch as we are already >>>> at >>>> v4 for something that was expected to be a trivial mechanical change. >>>> I >>>> would rather review the fix as a separate patch, maybe sent by you as >>>> you probably have a specific implementation in mind? >>> >>> #define ISOLATE_LOW_BIT(x) ({ \ >>> typeof(x) x_ = (x); \ >>> x_ & -x_; \ >>> }) >>> >>> Hard to see the scope creep here. What I would consider scope creep I >>> specifically didn't even ask for: I'd like this macro to be >>> overridable >>> by an arch. Specifically (see my earlier naming hint) I'd like to use >>> x86's BMI insn BLSI in the context of "x86: allow Kconfig control over >>> psABI level", when ABI v2 or higher is in use. >> >> I appreciate you suggesting an implementation; I'll send a v5 >> incorporating it. > > There's an issue with this approach, though: since the macro is used > indirectly > in expressions that are e.g. case labels or array sizes, the build fails > (see [1] for instance). > Perhaps it's best to leave it as is?
Hmm. I'm afraid it's not an option to "leave as is", not the least because - as said - I'm under the impression that another Misra rule requires macro arguments to be evaluated exactly once. Best I can think of right away is to have a macro for limited use (to address such build issues) plus an inline function (for general use). But yes, maybe that then indeed needs to be a 2nd step. Jan > [1] https://gitlab.com/xen-project/people/bugseng/xen/-/jobs/5423693947 >