linux-kernel - [PATCH 24/45] C++: Fix BUILD_BUG_ON

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Message-ID: <152261535982.30503.18110930471409401085.stgit@warthog.procyon.org.uk>
Date:   Sun, 01 Apr 2018 21:42:39 +0100
From:   David Howells <dhowells@...hat.com>
To:     linux-kernel@...r.kernel.org
Subject: [PATCH 24/45] C++: Fix BUILD_BUG_ON_ZERO()

Fix BUILD_BUG_ON_ZERO() to work in C++.  The construction format:

	(struct { ... })

is something C++ doesn't like.

Signed-off-by: David Howells <dhowells@...hat.com>
---

 include/linux/build_bug.h |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/include/linux/build_bug.h b/include/linux/build_bug.h
index 43d1fd50d433..7445385cd26f 100644
--- a/include/linux/build_bug.h
+++ b/include/linux/build_bug.h
@@ -20,13 +20,16 @@
 #define BUILD_BUG_ON_NOT_POWER_OF_2(n)			\
 	BUILD_BUG_ON((n) == 0 || (((n) & ((n) - 1)) != 0))
 
+extern int __build_bug_on_zero(void)
+	__compiletime_error("Build bug on zero");
+
 /*
  * Force a compilation error if condition is true, but also produce a
  * result (of value 0 and type size_t), so the expression can be used
  * e.g. in a structure initializer (or where-ever else comma expressions
  * aren't permitted).
  */
-#define BUILD_BUG_ON_ZERO(e) (sizeof(struct { int:(-!!(e)); }))
+#define BUILD_BUG_ON_ZERO(e)  ((e) ? 0 : __build_bug_on_zero())
 
 /*
  * BUILD_BUG_ON_INVALID() permits the compiler to check the validity of the