[patch 5/6] include/linux/compiler.h: don't perform compiletime_assert with -O0

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



From: Joe Stringer <joe@xxxxxxx>
Subject: include/linux/compiler.h: don't perform compiletime_assert with -O0

c7acec713d14c6c ("kernel.h: handle pointers to arrays better in
container_of()") made use of __compiletime_assert() from container_of()
thus increasing the usage of this macro, allowing developers to notice
type conflicts in usage of container_of() at compile time.

However, the implementation of __compiletime_assert relies on compiler
optimizations to report an error.  This means that if a developer uses
"-O0" with any code that performs container_of(), the compiler will always
report an error regardless of whether there is an actual problem in the
code.

This patch disables compile_time_assert when optimizations are disabled to
allow such code to compile with CFLAGS="-O0".

Example compilation failure:

./include/linux/compiler.h:547:38: error: call to `__compiletime_assert_94' declared with attribute error: pointer type mismatch in container_of()
  _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
                                      ^
./include/linux/compiler.h:530:4: note: in definition of macro `__compiletime_assert'
    prefix ## suffix();    \
    ^~~~~~
./include/linux/compiler.h:547:2: note: in expansion of macro `_compiletime_assert'
  _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
  ^~~~~~~~~~~~~~~~~~~
./include/linux/build_bug.h:46:37: note: in expansion of macro `compiletime_assert'
 #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
                                     ^~~~~~~~~~~~~~~~~~
./include/linux/kernel.h:860:2: note: in expansion of macro `BUILD_BUG_ON_MSG'
  BUILD_BUG_ON_MSG(!__same_type(*(ptr), ((type *)0)->member) && \
  ^~~~~~~~~~~~~~~~

[akpm@xxxxxxxxxxxxxxxxxxxx: use do{}while(0), per Michal]
Link: http://lkml.kernel.org/r/20170829230114.11662-1-joe@xxxxxxx
Fixes: c7acec713d14c6c ("kernel.h: handle pointers to arrays better in container_of()")
Signed-off-by: Joe Stringer <joe@xxxxxxx>
Cc: Ian Abbott <abbotti@xxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Michal Nazarewicz <mina86@xxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 include/linux/compiler.h |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff -puN include/linux/compiler.h~compiler-dont-perform-compiletime_assert-with-o0 include/linux/compiler.h
--- a/include/linux/compiler.h~compiler-dont-perform-compiletime_assert-with-o0
+++ a/include/linux/compiler.h
@@ -517,7 +517,8 @@ static __always_inline void __write_once
 # define __compiletime_error_fallback(condition) do { } while (0)
 #endif
 
-#define __compiletime_assert(condition, msg, prefix, suffix)		\
+#ifdef __OPTIMIZE__
+# define __compiletime_assert(condition, msg, prefix, suffix)		\
 	do {								\
 		bool __cond = !(condition);				\
 		extern void prefix ## suffix(void) __compiletime_error(msg); \
@@ -525,6 +526,9 @@ static __always_inline void __write_once
 			prefix ## suffix();				\
 		__compiletime_error_fallback(__cond);			\
 	} while (0)
+#else
+# define __compiletime_assert(condition, msg, prefix, suffix) do { } while (0)
+#endif
 
 #define _compiletime_assert(condition, msg, prefix, suffix) \
 	__compiletime_assert(condition, msg, prefix, suffix)
_
--
To unsubscribe from this list: send the line "unsubscribe mm-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html



[Index of Archives]     [Kernel Archive]     [IETF Annouce]     [DCCP]     [Netdev]     [Networking]     [Security]     [Bugtraq]     [Yosemite]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Linux SCSI]

  Powered by Linux