From mboxrd@z Thu Jan  1 00:00:00 1970
From: Yang Hongyang <yanghy@cn.fujitsu.com>
Subject: Re: [PATCH v4 06/14] tools/libxc: add a check in
 xc_hypercall_buffer_free_pages macro
Date: Wed, 13 May 2015 08:48:10 +0800
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To: Andrew Cooper <andrew.cooper3@citrix.com>, xen-devel@lists.xen.org
Cc: wei.liu2@citrix.com, ian.campbell@citrix.com, wency@cn.fujitsu.com, ian.jackson@eu.citrix.com, yunhong.jiang@intel.com, eddie.dong@intel.com, rshriram@cs.ubc.ca
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On 05/12/2015 08:10 PM, Andrew Cooper wrote:
> On 12/05/15 12:25, Yang Hongyang wrote:
>> When we use a DECLARE_HYPERCALL_BUFFER_SHADOW define a user
>> pointer '_name' and a shadow xc_hypercall_buffer_t.
>> then call xc_hypercall_buffer_free_pages(_xch, _name, _nr),
>> the complier will report '_name' unused error, it's because
>> xc_hypercall_buffer_free_pages() is a MACRO and '_name'
>> transparently converted to the hypercall buffer. it confused
>> the caller because xc_hypercall_buffer_free_pages() do look
>> like a function and take '_name' as an arg.
>> Add an if check to let the compiler think we are actually
>> using the argument '_name'.
>>
>> Signed-off-by: Yang Hongyang <yanghy@cn.fujitsu.com>
>> CC: Ian Campbell <Ian.Campbell@citrix.com>
>> CC: Ian Jackson <Ian.Jackson@eu.citrix.com>
>> CC: Wei Liu <wei.liu2@citrix.com>
>> CC: Andrew Cooper <andrew.cooper3@citrix.com>
>> ---
>>   tools/libxc/include/xenctrl.h | 4 +++-
>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/tools/libxc/include/xenctrl.h b/tools/libxc/include/xenctrl.h
>> index 0804257..35fb3ac 100644
>> --- a/tools/libxc/include/xenctrl.h
>> +++ b/tools/libxc/include/xenctrl.h
>> @@ -353,7 +353,9 @@ void xc__hypercall_buffer_free(xc_interface *xch, xc_hypercall_buffer_t *b);
>>   void *xc__hypercall_buffer_alloc_pages(xc_interface *xch, xc_hypercall_buffer_t *b, int nr_pages);
>>   #define xc_hypercall_buffer_alloc_pages(_xch, _name, _nr) xc__hypercall_buffer_alloc_pages(_xch, HYPERCALL_BUFFER(_name), _nr)
>>   void xc__hypercall_buffer_free_pages(xc_interface *xch, xc_hypercall_buffer_t *b, int nr_pages);
>> -#define xc_hypercall_buffer_free_pages(_xch, _name, _nr) xc__hypercall_buffer_free_pages(_xch, HYPERCALL_BUFFER(_name), _nr)
>> +#define xc_hypercall_buffer_free_pages(_xch, _name, _nr)        \
>> +    if ( _name )                                                \
>> +        xc__hypercall_buffer_free_pages(_xch, HYPERCALL_BUFFER(_name), _nr)
>
> This needs to be wrapped in a standard "do { ... } while (0)" for macros

Ok, thank you!

>
> ~Andrew
>
>>
>>   /*
>>    * Array of hypercall buffers.
>
> .
>

-- 
Thanks,
Yang.