Re: [Xen-devel] [PATCH] x86/xen: Remove use of VLAs

[Juergen Gross <jgross@xxxxxxxx>]

On 16/04/18 15:27, Boris Ostrovsky wrote:
> On 04/13/2018 06:11 PM, Laura Abbott wrote:
>> There's an ongoing effort to remove VLAs[1] from the kernel to eventually
>> turn on -Wvla. The few VLAs in use have an upper bound based on a size
>> of 64K. This doesn't produce an excessively large stack so just switch
>> the upper bound.
>>
>> [1] https://lkml.org/lkml/2018/3/7/621
>>
>> Signed-off-by: Laura Abbott <labbott@xxxxxxxxxx>
>> ---
>>  arch/x86/xen/enlighten_pv.c | 6 ++----
>>  1 file changed, 2 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
>> index c36d23aa6c35..d96a5a535cbb 100644
>> --- a/arch/x86/xen/enlighten_pv.c
>> +++ b/arch/x86/xen/enlighten_pv.c
>> @@ -421,8 +421,7 @@ static void xen_load_gdt(const struct desc_ptr *dtr)
>>  {
>>      unsigned long va = dtr->address;
>>      unsigned int size = dtr->size + 1;
>> -    unsigned pages = DIV_ROUND_UP(size, PAGE_SIZE);
> 
> 
> 
> Isn't dtr->size always either GDT_SIZE or 0?

GDT_SIZE - 1 :-)

>> -    unsigned long frames[pages];
>> +    unsigned long frames[DIV_ROUND_UP(SZ_64K, PAGE_SIZE)];

So we could just go with one frame and modify the BUG_ON() further below
accordingly.


Juergen

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