diff options
| author | Masahiro Yamada <yamada.masahiro@socionext.com> | 2018-08-26 03:16:29 +0900 |
|---|---|---|
| committer | Kees Cook <keescook@chromium.org> | 2018-10-11 08:17:50 -0700 |
| commit | 81b45683487a51b0f4d3b29d37f20d6d078544e4 (patch) | |
| tree | 96bb8fc0be10e5436b7c16a518a70dcfcf6a82ce /include/linux/compiler.h | |
| parent | 57361846b52bc686112da6ca5368d11210796804 (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.h | 17 |
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) |