From 540540d06e9d9b3769b46d88def90f7e7c002322 Mon Sep 17 00:00:00 2001 From: Marco Elver Date: Wed, 30 Jun 2021 18:56:49 -0700 Subject: kcov: add __no_sanitize_coverage to fix noinstr for all architectures Until now no compiler supported an attribute to disable coverage instrumentation as used by KCOV. To work around this limitation on x86, noinstr functions have their coverage instrumentation turned into nops by objtool. However, this solution doesn't scale automatically to other architectures, such as arm64, which are migrating to use the generic entry code. Clang [1] and GCC [2] have added support for the attribute recently. [1] https://github.com/llvm/llvm-project/commit/280333021e9550d80f5c1152a34e33e81df1e178 [2] https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=cec4d4a6782c9bd8d071839c50a239c49caca689 The changes will appear in Clang 13 and GCC 12. Add __no_sanitize_coverage for both compilers, and add it to noinstr. Note: In the Clang case, __has_feature(coverage_sanitizer) is only true if the feature is enabled, and therefore we do not require an additional defined(CONFIG_KCOV) (like in the GCC case where __has_attribute(..) is always true) to avoid adding redundant attributes to functions if KCOV is off. That being said, compilers that support the attribute will not generate errors/warnings if the attribute is redundantly used; however, where possible let's avoid it as it reduces preprocessed code size and associated compile-time overheads. [elver@google.com: Implement __has_feature(coverage_sanitizer) in Clang] Link: https://lkml.kernel.org/r/20210527162655.3246381-1-elver@google.com [elver@google.com: add comment explaining __has_feature() in Clang] Link: https://lkml.kernel.org/r/20210527194448.3470080-1-elver@google.com Link: https://lkml.kernel.org/r/20210525175819.699786-1-elver@google.com Signed-off-by: Marco Elver Acked-by: Peter Zijlstra (Intel) Reviewed-by: Miguel Ojeda Reviewed-by: Nathan Chancellor Cc: Nick Desaulniers Cc: Kees Cook Cc: Will Deacon Cc: Ard Biesheuvel Cc: Luc Van Oostenryck Cc: Arvind Sankar Cc: Masahiro Yamada Cc: Sami Tolvanen Cc: Arnd Bergmann Cc: Dmitry Vyukov Cc: Mark Rutland Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/compiler-clang.h | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) (limited to 'include/linux/compiler-clang.h') diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h index adbe76b203e2..49b0ac8b6fd3 100644 --- a/include/linux/compiler-clang.h +++ b/include/linux/compiler-clang.h @@ -13,6 +13,12 @@ /* all clang versions usable with the kernel support KASAN ABI version 5 */ #define KASAN_ABI_VERSION 5 +/* + * Note: Checking __has_feature(*_sanitizer) is only true if the feature is + * enabled. Therefore it is not required to additionally check defined(CONFIG_*) + * to avoid adding redundant attributes in other configurations. + */ + #if __has_feature(address_sanitizer) || __has_feature(hwaddress_sanitizer) /* Emulate GCC's __SANITIZE_ADDRESS__ flag */ #define __SANITIZE_ADDRESS__ @@ -45,6 +51,17 @@ #define __no_sanitize_undefined #endif +/* + * Support for __has_feature(coverage_sanitizer) was added in Clang 13 together + * with no_sanitize("coverage"). Prior versions of Clang support coverage + * instrumentation, but cannot be queried for support by the preprocessor. + */ +#if __has_feature(coverage_sanitizer) +#define __no_sanitize_coverage __attribute__((no_sanitize("coverage"))) +#else +#define __no_sanitize_coverage +#endif + /* * Not all versions of clang implement the type-generic versions * of the builtin overflow checkers. Fortunately, clang implements -- cgit v1.2.3-59-g8ed1b