linux-kernel - [PATCH] compiler.h: Fix undefined BUILD_BUG_ON

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Message-ID: <20241115204602.249590-1-philipp.reisner@linbit.com>
Date: Fri, 15 Nov 2024 21:46:02 +0100
From: Philipp Reisner <philipp.reisner@...bit.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Kees Cook <keescook@...omium.org>,
	Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
	linux-sparse@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] compiler.h: Fix undefined BUILD_BUG_ON_ZERO()

<linux/compiler.h> defines __must_be_array() and __must_be_cstr() and
both expand to BUILD_BUG_ON_ZERO(), but <linux/build_bug.h> defines
BUILD_BUG_ON_ZERO(). Including <linux/build_bug.h> in
<linux/compiler.h> would create a cyclic dependency as
<linux/build_bug.h> already includes <linux/compiler.h>.

Fix that by defining __BUILD_BUG_ON_ZERO_MSG() in <linux/compiler.h>
and using that for __must_be_array() and __must_be_cstr().

Signed-off-by: Philipp Reisner <philipp.reisner@...bit.com>
---
 include/linux/compiler.h | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 4d4e23b6e3e7..469a64dd6495 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -239,11 +239,18 @@ static inline void *offset_to_ptr(const int *off)
 
 #endif /* __ASSEMBLY__ */
 
+#ifdef __CHECKER__
+#define __BUILD_BUG_ON_ZERO_MSG(e, msg) (0)
+#else /* __CHECKER__ */
+#define __BUILD_BUG_ON_ZERO_MSG(e, msg) ((int)sizeof(struct {_Static_assert(!(e), msg);}))
+#endif /* __CHECKER__ */
+
 /* &a[0] degrades to a pointer: a different type from an array */
-#define __must_be_array(a)	BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))
+#define __must_be_array(a)	__BUILD_BUG_ON_ZERO_MSG(__same_type((a), &(a)[0]), "must be array")
 
 /* Require C Strings (i.e. NUL-terminated) lack the "nonstring" attribute. */
-#define __must_be_cstr(p)	BUILD_BUG_ON_ZERO(__annotated(p, nonstring))
+#define __must_be_cstr(p) \
+	__BUILD_BUG_ON_ZERO_MSG(__annotated(p, nonstring), "must be cstr (NUL-terminated)")
 
 /*
  * This returns a constant expression while determining if an argument is
-- 
2.47.0