[PATCH] 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 the WARN_ON() doesn't return whether a warning. Such
construction can be handy to have if you have to print more information
and now the stack track.

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>

---

This will be used in the SMMUv3 driver (see [1]).
---
 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 a9679c913d5c..d10c68aa3c07 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