From: Rasmus Villemoes linux@rasmusvillemoes.dk
mainline inclusion from mainline-v5.1-rc1 commit 6bab69c65013bed5fce9f101a64a84d0385b3946 category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/I4MKP4 CVE: NA
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BUILD_BUG_ON() is a little annoying, since it cannot be used outside function scope. So one cannot put assertions about the sizeof() a struct next to the struct definition, but has to hide that in some more or less arbitrary function.
Since gcc 4.6 (which is now also the required minimum), there is support for the C11 _Static_assert in all C modes, including gnu89. So add a simple wrapper for that.
_Static_assert() requires a message argument, which is usually quite redundant (and I believe that bug got fixed at least in newer C++ standards), but we can easily work around that with a little macro magic, making it optional.
For example, adding
static_assert(sizeof(struct printf_spec) == 8);
in vsprintf.c and modifying that struct to violate it, one gets
./include/linux/build_bug.h:78:41: error: static assertion failed: "sizeof(struct printf_spec) == 8" #define __static_assert(expr, msg, ...) _Static_assert(expr, "" msg "")
godbolt.org suggests that _Static_assert() has been support by clang since at least 3.0.0.
Link: http://lkml.kernel.org/r/20190208203015.29702-1-linux@rasmusvillemoes.dk Signed-off-by: Rasmus Villemoes linux@rasmusvillemoes.dk Acked-by: Alexey Dobriyan adobriyan@gmail.com Cc: Masahiro Yamada yamada.masahiro@socionext.com Cc: Nick Desaulniers ndesaulniers@google.com Cc: Kees Cook keescook@chromium.org Cc: Luc Van Oostenryck luc.vanoostenryck@gmail.com Cc: Alexander Viro viro@zeniv.linux.org.uk Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Jackie Liu liuyun01@kylinos.cn Signed-off-by: Laibin Qiu qiulaibin@huawei.com --- include/linux/build_bug.h | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+)
diff --git a/include/linux/build_bug.h b/include/linux/build_bug.h index 219d24e19de0..e8fe68102c1e 100644 --- a/include/linux/build_bug.h +++ b/include/linux/build_bug.h @@ -72,4 +72,23 @@ */ #define BUILD_BUG() BUILD_BUG_ON_MSG(1, "BUILD_BUG failed")
+/** + * static_assert - check integer constant expression at build time + * + * static_assert() is a wrapper for the C11 _Static_assert, with a + * little macro magic to make the message optional (defaulting to the + * stringification of the tested expression). + * + * Contrary to BUILD_BUG_ON(), static_assert() can be used at global + * scope, but requires the expression to be an integer constant + * expression (i.e., it is not enough that __builtin_constant_p() is + * true for expr). + * + * Also note that BUILD_BUG_ON() fails the build if the condition is + * true, while static_assert() fails the build if the expression is + * false. + */ +#define static_assert(expr, ...) __static_assert(expr, ##__VA_ARGS__, #expr) +#define __static_assert(expr, msg, ...) _Static_assert(expr, msg) + #endif /* _LINUX_BUILD_BUG_H */