Re: [Xen-devel] [PATCH 6/8] xen/x86: Avoid overriding initialisers in arrays

[George Dunlap <george.dunlap@xxxxxxxxxx>]

On 09/02/16 20:01, Andrew Cooper wrote:
> Clang objects to having multiple initialisers when creating an array.
> 
> As this warning is useful for spotting obscure bugs, disabling it is
> unhelpful.  Instead, fix our two deliberate usecases.
> 
> In the p2m-ept case, pull the array out into a helper function, so the helper
> can guarentee to cover the NULL pointer case.
> 
> No functional change.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Acked-by: George Dunlap <george.dunlap@xxxxxxxxxx>

> ---
> CC: Jan Beulich <JBeulich@xxxxxxxx>
> CC: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
> CC: Jun Nakajima <jun.nakajima@xxxxxxxxx>
> CC: Kevin Tian <kevin.tian@xxxxxxxxx>
> ---
>  xen/arch/x86/cpu/mtrr/generic.c |  3 +--
>  xen/arch/x86/mm/p2m-ept.c       | 27 ++++++++++++++++-----------
>  2 files changed, 17 insertions(+), 13 deletions(-)
> 
> diff --git a/xen/arch/x86/cpu/mtrr/generic.c b/xen/arch/x86/cpu/mtrr/generic.c
> index ea0efe2..8839f8d 100644
> --- a/xen/arch/x86/cpu/mtrr/generic.c
> +++ b/xen/arch/x86/cpu/mtrr/generic.c
> @@ -91,7 +91,6 @@ static const char *__init mtrr_attrib_to_str(mtrr_type x)
>  {
>       static const char __initconst strings[MTRR_NUM_TYPES][16] =
>       {
> -             [0 ... MTRR_NUM_TYPES - 1] = "?",
>               [MTRR_TYPE_UNCACHABLE]     = "uncachable",
>               [MTRR_TYPE_WRCOMB]         = "write-combining",
>               [MTRR_TYPE_WRTHROUGH]      = "write-through",
> @@ -99,7 +98,7 @@ static const char *__init mtrr_attrib_to_str(mtrr_type x)
>               [MTRR_TYPE_WRBACK]         = "write-back",
>       };
>  
> -     return x < MTRR_NUM_TYPES ? strings[x] : "?";
> +     return x < MTRR_NUM_TYPES ? (strings[x] ?: "?") : "?";
>  }
>  
>  static unsigned int __initdata last_fixed_start;
> diff --git a/xen/arch/x86/mm/p2m-ept.c b/xen/arch/x86/mm/p2m-ept.c
> index c094320..c5fe906 100644
> --- a/xen/arch/x86/mm/p2m-ept.c
> +++ b/xen/arch/x86/mm/p2m-ept.c
> @@ -1201,6 +1201,20 @@ void ept_p2m_uninit(struct p2m_domain *p2m)
>      free_cpumask_var(ept->invalidate);
>  }
>  
> +static const char *memory_type_to_str(unsigned int x)
> +{
> +    static const char memory_types[8][2] = {
> +        [MTRR_TYPE_UNCACHABLE]     = "UC",
> +        [MTRR_TYPE_WRCOMB]         = "WC",
> +        [MTRR_TYPE_WRTHROUGH]      = "WT",
> +        [MTRR_TYPE_WRPROT]         = "WP",
> +        [MTRR_TYPE_WRBACK]         = "WB",
> +        [MTRR_NUM_TYPES]           = "??"
> +    };
> +
> +    return x < ARRAY_SIZE(memory_types) ? (memory_types[x] ?: "?") : "?";
> +}
> +
>  static void ept_dump_p2m_table(unsigned char key)
>  {
>      struct domain *d;
> @@ -1212,15 +1226,6 @@ static void ept_dump_p2m_table(unsigned char key)
>      unsigned long record_counter = 0;
>      struct p2m_domain *p2m;
>      struct ept_data *ept;
> -    static const char memory_types[8][2] = {
> -        [0 ... 7] = "?",
> -        [MTRR_TYPE_UNCACHABLE]     = "UC",
> -        [MTRR_TYPE_WRCOMB]         = "WC",
> -        [MTRR_TYPE_WRTHROUGH]      = "WT",
> -        [MTRR_TYPE_WRPROT]         = "WP",
> -        [MTRR_TYPE_WRBACK]         = "WB",
> -        [MTRR_NUM_TYPES]           = "??"
> -    };
>  
>      for_each_domain(d)
>      {
> @@ -1260,8 +1265,8 @@ static void ept_dump_p2m_table(unsigned char key)
>                             ept_entry->r ? 'r' : ' ',
>                             ept_entry->w ? 'w' : ' ',
>                             ept_entry->x ? 'x' : ' ',
> -                           memory_types[ept_entry->emt][0],
> -                           memory_types[ept_entry->emt][1]
> +                           memory_type_to_str(ept_entry->emt)[0],
> +                           memory_type_to_str(ept_entry->emt)[1]
>                             ?: ept_entry->emt + '0',
>                             c ?: ept_entry->ipat ? '!' : ' ');
>  
> 


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