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Date:   Fri, 19 Jun 2020 20:30:06 -0700
From:   Kees Cook <keescook@...omium.org>
To:     linux-kernel@...r.kernel.org
Cc:     Kees Cook <keescook@...omium.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Bart van Assche <bvanassche@....org>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Joe Perches <joe@...ches.com>,
        Andy Whitcroft <apw@...onical.com>, x86@...nel.org,
        drbd-dev@...ts.linbit.com, linux-block@...r.kernel.org,
        b43-dev@...ts.infradead.org, netdev@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-wireless@...r.kernel.org,
        linux-ide@...r.kernel.org, linux-clk@...r.kernel.org,
        linux-spi@...r.kernel.org, linux-mm@...ck.org,
        clang-built-linux@...glegroups.com
Subject: [PATCH v2 16/16] compiler: Remove uninitialized_var() macro

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. With the recent
change to disable -Wmaybe-uninitialized in v5.7 in commit 78a5255ffb6a
("Stop the ad-hoc games with -Wno-maybe-initialized"), this is likely
the best time to make this treewide change.

[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@...ux-foundation.org>
Reviewed-by: Bart van Assche <bvanassche@....org>
Reviewed-by: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
Tested-by: Nathan Chancellor <natechancellor@...il.com>
Tested-by: Sedat Dilek <sedat.dilek@...il.com>
Signed-off-by: Kees Cook <keescook@...omium.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 ee37256ec8bd..f2371b83aaf2 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 7dd4e0349ef3..84e099a87383 100644
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -59,12 +59,6 @@
 	(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 9f9002734e19..2f2f4082225e 100644
--- a/tools/include/linux/compiler.h
+++ b/tools/include/linux/compiler.h
@@ -111,8 +111,6 @@
 # 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

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