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authorMasahiro Yamada <yamada.masahiro@socionext.com>2018-08-26 03:16:29 +0900
committerKees Cook <keescook@chromium.org>2018-10-11 08:17:50 -0700
commit81b45683487a51b0f4d3b29d37f20d6d078544e4 (patch)
tree96bb8fc0be10e5436b7c16a518a70dcfcf6a82ce /include/linux/compiler.h
parent57361846b52bc686112da6ca5368d11210796804 (diff)
compiler.h: give up __compiletime_assert_fallback()
__compiletime_assert_fallback() is supposed to stop building earlier by using the negative-array-size method in case the compiler does not support "error" attribute, but has never worked like that. You can simply try: BUILD_BUG_ON(1); GCC immediately terminates the build, but Clang does not report anything because Clang does not support the "error" attribute now. It will later fail at link time, but __compiletime_assert_fallback() is not working at least. The root cause is commit 1d6a0d19c855 ("bug.h: prevent double evaluation of `condition' in BUILD_BUG_ON"). Prior to that commit, BUILD_BUG_ON() was checked by the negative-array-size method *and* the link-time trick. Since that commit, the negative-array-size is not effective because '__cond' is no longer constant. As the comment in <linux/build_bug.h> says, GCC (and Clang as well) only emits the error for obvious cases. When '__cond' is a variable, ((void)sizeof(char[1 - 2 * __cond])) ... is not obvious for the compiler to know the array size is negative. Reverting that commit would break BUILD_BUG() because negative-size-array is evaluated before the code is optimized out. Let's give up __compiletime_assert_fallback(). This commit does not change the current behavior since it just rips off the useless code. Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com> Reviewed-by: Kees Cook <keescook@chromium.org> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> Signed-off-by: Kees Cook <keescook@chromium.org>
Diffstat (limited to 'include/linux/compiler.h')
-rw-r--r--include/linux/compiler.h17
1 files changed, 1 insertions, 16 deletions
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 681d866efb1e..87c776c3ce73 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -314,29 +314,14 @@ static inline void *offset_to_ptr(const int *off)
#endif
#ifndef __compiletime_error
# define __compiletime_error(message)
-/*
- * Sparse complains of variable sized arrays due to the temporary variable in
- * __compiletime_assert. Unfortunately we can't just expand it out to make
- * sparse see a constant array size without breaking compiletime_assert on old
- * versions of GCC (e.g. 4.2.4), so hide the array from sparse altogether.
- */
-# ifndef __CHECKER__
-# define __compiletime_error_fallback(condition) \
- do { ((void)sizeof(char[1 - 2 * condition])); } while (0)
-# endif
-#endif
-#ifndef __compiletime_error_fallback
-# define __compiletime_error_fallback(condition) do { } while (0)
#endif
#ifdef __OPTIMIZE__
# define __compiletime_assert(condition, msg, prefix, suffix) \
do { \
- int __cond = !(condition); \
extern void prefix ## suffix(void) __compiletime_error(msg); \
- if (__cond) \
+ if (!(condition)) \
prefix ## suffix(); \
- __compiletime_error_fallback(__cond); \
} while (0)
#else
# define __compiletime_assert(condition, msg, prefix, suffix) do { } while (0)