[PATCH v2] xen: Rework WARN_ON() to return whether a warning was triggered

[Julien Grall <julien@xxxxxxx>]

From: Julien Grall <jgrall@xxxxxxxxxx>

So far, our implementation of WARN_ON() cannot be used in the following
situation:

if ( WARN_ON() )
    ...

This is because WARN_ON() doesn't return whether a warning has been
triggered. Such construciton can be handy if you want to print more
information and also dump the stack trace.

Therefore, rework the WARN_ON() implementation to return whether a
warning was triggered. The idea was borrowed from Linux

Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>
Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
Reviewed-by: Bertrand Marquis <bertrand.marquis@xxxxxxx>

---
    Changes in v2:
        - Rework the commit message
        - Don't use trailing underscore
        - Add Bertrand's and Juergen's reviewed-by
---
 xen/include/xen/lib.h | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/xen/include/xen/lib.h b/xen/include/xen/lib.h
index 48429b69b8df..5841bd489c35 100644
--- a/xen/include/xen/lib.h
+++ b/xen/include/xen/lib.h
@@ -23,7 +23,13 @@
 #include <asm/bug.h>
 
 #define BUG_ON(p)  do { if (unlikely(p)) BUG();  } while (0)
-#define WARN_ON(p) do { if (unlikely(p)) WARN(); } while (0)
+#define WARN_ON(p)  ({                  \
+    bool ret_warn_on_ = (p);            \
+                                        \
+    if ( unlikely(ret_warn_on_) )       \
+        WARN();                         \
+    unlikely(ret_warn_on_);             \
+})
 
 /* All clang versions supported by Xen have _Static_assert. */
 #if defined(__clang__) || \
-- 
2.17.1