From: Marco Elver elver@google.com
[ Upstream commit 540540d06e9d9b3769b46d88def90f7e7c002322 ]
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/280333021e9550d80f5c1152a34e33e8... [2] https://gcc.gnu.org/git/?p=gcc.git%3Ba=commit%3Bh=cec4d4a6782c9bd8d071839c50... 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 elver@google.com Acked-by: Peter Zijlstra (Intel) peterz@infradead.org Reviewed-by: Miguel Ojeda ojeda@kernel.org Reviewed-by: Nathan Chancellor nathan@kernel.org Cc: Nick Desaulniers ndesaulniers@google.com Cc: Kees Cook keescook@chromium.org Cc: Will Deacon will@kernel.org Cc: Ard Biesheuvel ardb@kernel.org Cc: Luc Van Oostenryck luc.vanoostenryck@gmail.com Cc: Arvind Sankar nivedita@alum.mit.edu Cc: Masahiro Yamada masahiroy@kernel.org Cc: Sami Tolvanen samitolvanen@google.com Cc: Arnd Bergmann arnd@arndb.de Cc: Dmitry Vyukov dvyukov@google.com Cc: Mark Rutland mark.rutland@arm.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- include/linux/compiler-clang.h | 17 +++++++++++++++++ include/linux/compiler-gcc.h | 6 ++++++ include/linux/compiler_types.h | 2 +- 3 files changed, 24 insertions(+), 1 deletion(-)
diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h index d217c382b02d..4d87b36dbc8c 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 diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h index 48750243db4c..c6ab0dcb9c0c 100644 --- a/include/linux/compiler-gcc.h +++ b/include/linux/compiler-gcc.h @@ -126,6 +126,12 @@ #define __no_sanitize_undefined #endif
+#if defined(CONFIG_KCOV) && __has_attribute(__no_sanitize_coverage__) +#define __no_sanitize_coverage __attribute__((no_sanitize_coverage)) +#else +#define __no_sanitize_coverage +#endif + #if GCC_VERSION >= 50100 #define COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW 1 #endif diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h index e5dd5a4ae946..652217da3b7c 100644 --- a/include/linux/compiler_types.h +++ b/include/linux/compiler_types.h @@ -210,7 +210,7 @@ struct ftrace_likely_data { /* Section for code which can't be instrumented at all */ #define noinstr \ noinline notrace __attribute((__section__(".noinstr.text"))) \ - __no_kcsan __no_sanitize_address + __no_kcsan __no_sanitize_address __no_sanitize_coverage
#endif /* __KERNEL__ */