Messages in this thread | | | Subject | Re: [PATCH] x86: xen: remove the use of VLAIS | From | Juergen Gross <> | Date | Tue, 2 Jan 2018 09:18:40 +0100 |
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On 24/12/17 19:02, Nick Desaulniers wrote: > Variable Length Arrays In Structs (VLAIS) is not supported by Clang, and > frowned upon by others. > > https://lkml.org/lkml/2013/9/23/500 > > Here, the VLAIS was used because the size of the bitmap returned from > xen_mc_entry() depended on possibly (based on kernel configuration) > runtime sized data. Rather than declaring args as a VLAIS then calling > sizeof on *args, we can define the variable length array (mask) to be a > pointer, and calculate the appropriate sizeof args manually. Further, we > can get rid of the #ifdef's and rely on num_possible_cpus() (thanks to a > helpful checkpatch warning from an earlier version of this patch).
Using a pointer for mask seems to be wrong, as it is never initialized.
Why don't you just use:
DECLARE_BITMAP(mask, NR_CPUS);
and drop the #ifdef, while keeping the manual length calculation?
Juergen
> > Signed-off-by: Nick Desaulniers <nick.desaulniers@gmail.com> > --- > arch/x86/xen/mmu_pv.c | 10 ++++------ > 1 file changed, 4 insertions(+), 6 deletions(-) > > diff --git a/arch/x86/xen/mmu_pv.c b/arch/x86/xen/mmu_pv.c > index 4d62c07..966976c 100644 > --- a/arch/x86/xen/mmu_pv.c > +++ b/arch/x86/xen/mmu_pv.c > @@ -1325,20 +1325,18 @@ static void xen_flush_tlb_others(const struct cpumask *cpus, > { > struct { > struct mmuext_op op; > -#ifdef CONFIG_SMP > - DECLARE_BITMAP(mask, num_processors); > -#else > - DECLARE_BITMAP(mask, NR_CPUS); > -#endif > + unsigned long *mask; > } *args; > struct multicall_space mcs; > + const size_t mc_entry_size = sizeof(args->op) + > + sizeof(*args->mask) * BITS_TO_LONGS(num_possible_cpus()); > > trace_xen_mmu_flush_tlb_others(cpus, info->mm, info->start, info->end); > > if (cpumask_empty(cpus)) > return; /* nothing to do */ > > - mcs = xen_mc_entry(sizeof(*args)); > + mcs = xen_mc_entry(mc_entry_size); > args = mcs.args; > args->op.arg2.vcpumask = to_cpumask(args->mask); > >
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