Commit 63a0895d authored Jun 03, 2020 by Kees Cook

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 78a5255f
("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@linux-foundation.org>
Reviewed-by: Bart van Assche <bvanassche@acm.org>
Reviewed-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Tested-by: Nathan Chancellor <natechancellor@gmail.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>

parent 3f649ab7

include/linux/compiler-clang.h

+0 −2

Original line number	Diff line number	Diff line
		@@ -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
		*/

include/linux/compiler-gcc.h

+0 −6

Original line number	Diff line number	Diff line
		@@ -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

tools/include/linux/compiler.h

+0 −2

Original line number	Diff line number	Diff line
		@@ -111,8 +111,6 @@
		# define noinline
		#endif

		#define uninitialized_var(x) x = *(&(x))

		#include <linux/types.h>

		/*

tools/virtio/linux/kernel.h

+0 −2

Original line number	Diff line number	Diff line
		@@ -110,8 +110,6 @@ 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

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