[PATCH 10/10] compiler: Remove uninitialized_var() macro

From: Kees Cook <keescook@chromium.org>
To: linux-kernel@vger.kernel.org
Cc: Kees Cook <keescook@chromium.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>,
	Alexander Potapenko <glider@google.com>,
	Joe Perches <joe@perches.com>, Andy Whitcroft <apw@canonical.com>,
	x86@kernel.org, drbd-dev@lists.linbit.com,
	linux-block@vger.kernel.org, b43-dev@lists.infradead.org,
	netdev@vger.kernel.org, linux-wireless@vger.kernel.org,
	linux-ide@vger.kernel.org, linux-clk@vger.kernel.org,
	linux-spi@vger.kernel.org, linux-mm@kvack.org,
	clang-built-linux@googlegroups.com
Subject: [PATCH 10/10] compiler: Remove uninitialized_var() macro
Date: Wed,  3 Jun 2020 16:32:03 -0700	[thread overview]
Message-ID: <20200603233203.1695403-11-keescook@chromium.org> (raw)
In-Reply-To: <20200603233203.1695403-1-keescook@chromium.org>

Using uninitialized_var() is dangerous as it papers over real bugs[1]
(or can in the future), and suppresses unrelated compiler warnings
(e.g. "unused variable"). If the compiler thinks it is uninitialized,
either simply initialize the variable or make compiler changes.

As recommended[2] by[3] Linus[4], remove the macro.

[1] https://lore.kernel.org/lkml/20200603174714.192027-1-glider@google.com/
[2] https://lore.kernel.org/lkml/CA+55aFw+Vbj0i=1TGqCR5vQkCzWJ0QxK6CernOU6eedsudAixw@mail.gmail.com/
[3] https://lore.kernel.org/lkml/CA+55aFwgbgqhbp1fkxvRKEpzyR5J8n1vKT1VZdz9knmPuXhOeg@mail.gmail.com/
[4] https://lore.kernel.org/lkml/CA+55aFz2500WfbKXAx8s67wrm9=yVJu65TpLgN_ybYNv0VEOKA@mail.gmail.com/

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 include/linux/compiler-clang.h | 2 --
 include/linux/compiler-gcc.h   | 6 ------
 tools/include/linux/compiler.h | 2 --
 tools/virtio/linux/kernel.h    | 2 --
 4 files changed, 12 deletions(-)

diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
index 790c0c6b8552..019f444b500b 100644
--- a/include/linux/compiler-clang.h
+++ b/include/linux/compiler-clang.h
@@ -5,8 +5,6 @@
 
 /* Compiler specific definitions for Clang compiler */
 
-#define uninitialized_var(x) x = *(&(x))
-
 /* same as gcc, this was present in clang-2.6 so we can assume it works
  * with any version that can compile the kernel
  */
diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index d7ee4c6bad48..ac3e29ae32de 100644
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -58,12 +58,6 @@
 	(typeof(ptr)) (__ptr + (off));					\
 })
 
-/*
- * A trick to suppress uninitialized variable warning without generating any
- * code
- */
-#define uninitialized_var(x) x = x
-
 #ifdef CONFIG_RETPOLINE
 #define __noretpoline __attribute__((__indirect_branch__("keep")))
 #endif
diff --git a/tools/include/linux/compiler.h b/tools/include/linux/compiler.h
index 180f7714a5f1..29cbb73f2ae0 100644
--- a/tools/include/linux/compiler.h
+++ b/tools/include/linux/compiler.h
@@ -108,8 +108,6 @@
 # define noinline
 #endif
 
-#define uninitialized_var(x) x = *(&(x))
-
 #include <linux/types.h>
 
 /*
diff --git a/tools/virtio/linux/kernel.h b/tools/virtio/linux/kernel.h
index 6683b4a70b05..1e14ab967c11 100644
--- a/tools/virtio/linux/kernel.h
+++ b/tools/virtio/linux/kernel.h
@@ -109,8 +109,6 @@ static inline void free_page(unsigned long addr)
 	const typeof( ((type *)0)->member ) *__mptr = (ptr);	\
 	(type *)( (char *)__mptr - offsetof(type,member) );})
 
-#define uninitialized_var(x) x = x
-
 # ifndef likely
 #  define likely(x)	(__builtin_expect(!!(x), 1))
 # endif
-- 
2.25.1

