tools/libxc: add a check in xc_hypercall_buffer_free_pages macro

When we use a DECLARE_HYPERCALL_BUFFER_SHADOW it defines a user
pointer '_name' and a shadow xc_hypercall_buffer_t.
When calling xc_hypercall_buffer_free_pages(_xch, _name, _nr),
the complier will report '_name' unused error, because
xc_hypercall_buffer_free_pages() is a MACRO and '_name' is
transparently converted to the hypercall buffer. it confuses
the caller because xc_hypercall_buffer_free_pages() looks
like a function and takes '_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>
Acked-by: Ian Campbell <Ian.Campbell@citrix.com>
[ ijc -- some rewording of the commit message ]

diff --git a/tools/libxc/include/xenctrl.h b/tools/libxc/include/xenctrl.h
index 5a9f76a9ab7e794a211d75720b39b9a13a7993e5..09a7450519e88d96f005e6b6963dafa76decd142 100644 (file)
--- a/tools/libxc/include/xenctrl.h
+++ b/tools/libxc/include/xenctrl.h
@@ -358,7 +358,12 @@ 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.