[PATCH v5 06/14] tools/libxc: add a check in xc_hypercall_buffer_free_pages macro

[Yang Hongyang <yanghy@cn.fujitsu.com>]

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 | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/tools/libxc/include/xenctrl.h b/tools/libxc/include/xenctrl.h
index 0804257..202f612 100644
--- a/tools/libxc/include/xenctrl.h
+++ b/tools/libxc/include/xenctrl.h
@@ -353,7 +353,12 @@ 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)                    \
+    do {                                                                    \
+        if ( _name )                                                        \
+            xc__hypercall_buffer_free_pages(_xch, HYPERCALL_BUFFER(_name),  \
+                                            _nr);                           \
+    } while (0)
 
 /*
  * Array of hypercall buffers.
-- 
1.9.1