linux-kernel - [PATCH 3/5] compiler_types: Introduce __is

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Message-Id: <20250321204105.1898507-3-kees@kernel.org>
Date: Fri, 21 Mar 2025 13:40:59 -0700
From: Kees Cook <kees@...nel.org>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Kees Cook <kees@...nel.org>,
	Miguel Ojeda <ojeda@...nel.org>,
	Nathan Chancellor <nathan@...nel.org>,
	Marco Elver <elver@...gle.com>,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	Przemek Kitszel <przemyslaw.kitszel@...el.com>,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	Hyeonggon Yoo <42.hyeyoo@...il.com>,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	linux-hardening@...r.kernel.org
Subject: [PATCH 3/5] compiler_types: Introduce __is_lvalue()

If __builtin_is_lvalue() is available, use it with __is_lvalue(). There
is patch to Clang to provide this builtin now[1].

Link: https://github.com/kees/llvm-project/commits/builtin_is_lvalue/ [1]
Signed-off-by: Kees Cook <kees@...nel.org>
---
Cc: Miguel Ojeda <ojeda@...nel.org>
Cc: Nathan Chancellor <nathan@...nel.org>
Cc: Marco Elver <elver@...gle.com>
Cc: Nick Desaulniers <ndesaulniers@...gle.com>
Cc: Przemek Kitszel <przemyslaw.kitszel@...el.com>
---
 include/linux/compiler_types.h | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
index e09d323be845..eb016808dfa8 100644
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -468,6 +468,16 @@ struct ftrace_likely_data {
 #define __annotated(var, attr)	__builtin_has_attribute(var, attr)
 #endif
 
+/*
+ * Determine if a given expression is an lvalue for potential
+ * assignment. Without the builtin, report nothing is an lvalue.
+ */
+#if __has_builtin(__builtin_is_lvalue)
+#define __is_lvalue(expr)	__builtin_is_lvalue(expr)
+#else
+#define __is_lvalue(expr)	false
+#endif
+
 /*
  * Some versions of gcc do not mark 'asm goto' volatile:
  *
-- 
2.34.1