On 12.01.2022 10:28, Jan Beulich wrote: > On 12.01.2022 10:22, Andrew Cooper wrote: >> On 12/01/2022 09:00, Jan Beulich wrote: >>> When the macro's "return value" is not used, the macro use can be >>> replaced by a simply division, avoiding some obfuscation. >>> >>> According to my observations, no change to generated code. >>> >>> Signed-off-by: Jan Beulich <jbeul...@suse.com> >> >> I like this change in principle, but see below. >> >> do_div() needs to be deleted, because it's far too easy screw up. At a >> bare minimum, it should be replaced with a static inline that takes it's >> first parameter by pointer, because then at least every callsite reads >> correctly in terms of the C language. > > That ought to be a 2nd step, requiring agreement with Arm folks (and > adjustments to their code). > >>> --- a/xen/arch/x86/time.c >>> +++ b/xen/arch/x86/time.c >>> @@ -610,8 +610,7 @@ static uint64_t xen_timer_cpu_frequency( >>> struct vcpu_time_info *info = &this_cpu(vcpu_info)->time; >>> uint64_t freq; >>> >>> - freq = 1000000000ULL << 32; >>> - do_div(freq, info->tsc_to_system_mul); >>> + freq = (1000000000ULL << 32) / info->tsc_to_system_mul; >>> if ( info->tsc_shift < 0 ) >>> freq <<= -info->tsc_shift; >> >> do_div()'s output is consumed here. I don't think this hunk is safe to >> convert. > > If by "output" you mean its "return value", then it clearly isn't > consumed. And I continue to think that I did express correctly the > effect do_div() did have on "freq".
I think I did address both points (the earlier one was actually more a remark imo anyway, not a request to change anything right in this patch), so may I please ask for an ack (or a response clarifying what I'm not understanding in what you have said)? Thanks, Jan
