On 06/10/2023 9:26 am, Nicola Vetrini wrote: > The COUNT_LEAVES macro is introduced to avoid using an essentially > boolean value in a subtraction. > > No functional change. > > Signed-off-by: Nicola Vetrini <nicola.vetr...@bugseng.com> > --- > xen/include/xen/lib/x86/cpu-policy.h | 13 +++++++------ > 1 file changed, 7 insertions(+), 6 deletions(-) > > diff --git a/xen/include/xen/lib/x86/cpu-policy.h > b/xen/include/xen/lib/x86/cpu-policy.h > index bab3eecda6c1..700993cc67e8 100644 > --- a/xen/include/xen/lib/x86/cpu-policy.h > +++ b/xen/include/xen/lib/x86/cpu-policy.h > @@ -95,17 +95,18 @@ const char *x86_cpuid_vendor_to_str(unsigned int vendor); > #define CPUID_GUEST_NR_EXTD MAX(CPUID_GUEST_NR_EXTD_INTEL, \ > CPUID_GUEST_NR_EXTD_AMD) > > +#define COUNT_LEAVES(X) ((X) - ((X) ? 1 : 0)) > /* > * Maximum number of leaves a struct cpu_policy turns into when serialised > for > * interaction with the toolstack. (Sum of all leaves in each union, less > the > * entries in basic which sub-unions hang off of.) > */ > -#define CPUID_MAX_SERIALISED_LEAVES \ > - (CPUID_GUEST_NR_BASIC + \ > - CPUID_GUEST_NR_FEAT - !!CPUID_GUEST_NR_FEAT + \ > - CPUID_GUEST_NR_CACHE - !!CPUID_GUEST_NR_CACHE + \ > - CPUID_GUEST_NR_TOPO - !!CPUID_GUEST_NR_TOPO + \ > - CPUID_GUEST_NR_XSTATE - !!CPUID_GUEST_NR_XSTATE + \ > +#define CPUID_MAX_SERIALISED_LEAVES \ > + (CPUID_GUEST_NR_BASIC + \ > + COUNT_LEAVES(CPUID_GUEST_NR_FEAT) + \ > + COUNT_LEAVES(CPUID_GUEST_NR_CACHE) + \ > + COUNT_LEAVES(CPUID_GUEST_NR_TOPO) + \ > + COUNT_LEAVES(CPUID_GUEST_NR_XSTATE) + \ > CPUID_GUEST_NR_EXTD + 2 /* hv_limit and hv2_limit */ )
This may not have been a MISRA-approved calculation, but encapsulating it like this breaks any ability to follow what's going on. CPUID data in x86 is mostly a sparse 1-D array (BASIC, EXTD, HV blocks), but a couple of elements in the BASIC array have arrays themselves. The struct is laid out for O(1) access, so you can't just say sizeof(struct) / sizeof(element). The BASIC array has elements (0x4, 0x7, 0xb, 0xd) which hold no data because there's actually an array elsewhere containing all the data. So logically, it's: (BASIC + (FEAT - 1) + (CACHE - 1) + (TOPO - 1) + (XSTATE - 1)) + EXTD + 2 And in practice I'd far rather express it with a plain -1 than a - !!NR_, if the latter isn't an option. Presumably MISRA would be happy with that? If so, I can submit a patch. There's also a typo in that the comment that wants fixing. ~Andrew
