linux-kernel - [PATCH 2/2] Kconfig: CC_HAS_NO_PROFILE_FN

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Date:   Fri, 18 Jun 2021 16:30:23 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Bill Wendling <wcw@...gle.com>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Peter Oberparleiter <oberpar@...ux.ibm.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Will Deacon <will@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com,
        x86@...nel.org, Borislav Petkov <bp@...en8.de>,
        Martin Liska <mliska@...e.cz>, Marco Elver <elver@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Fangrui Song <maskray@...gle.com>, linux-doc@...r.kernel.org,
        linux-kbuild@...r.kernel.org, Dmitry Vyukov <dvyukov@...gle.com>,
        johannes.berg@...el.com, linux-toolchains@...r.kernel.org,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: [PATCH 2/2] Kconfig: CC_HAS_NO_PROFILE_FN_ATTR, depend on for GCOV
 and PGO

We don't want compiler instrumentation to touch noinstr functions, which
are annotated with the no_profile function attribute. Add a Kconfig test
for this and make PGO and GCOV depend on it.

Cc: Masahiro Yamada <masahiroy@...nel.org>
Cc: Peter Oberparleiter <oberpar@...ux.ibm.com>
Link: https://lore.kernel.org/lkml/YMTn9yjuemKFLbws@hirez.programming.kicks-ass.net/
Link: https://lore.kernel.org/lkml/YMcssV%2Fn5IBGv4f0@hirez.programming.kicks-ass.net/
Suggested-by: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
---
 init/Kconfig        | 3 +++
 kernel/gcov/Kconfig | 1 +
 kernel/pgo/Kconfig  | 3 ++-
 3 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/init/Kconfig b/init/Kconfig
index 1ea12c64e4c9..540f862b40c6 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -83,6 +83,9 @@ config TOOLS_SUPPORT_RELR
 config CC_HAS_ASM_INLINE
 	def_bool $(success,echo 'void foo(void) { asm inline (""); }' | $(CC) -x c - -c -o /dev/null)
 
+config CC_HAS_NO_PROFILE_FN_ATTR
+	def_bool $(success,echo '__attribute__((no_profile)) int x();' | $(CC) -x c - -c -o /dev/null -Werror)
+
 config CONSTRUCTORS
 	bool
 
diff --git a/kernel/gcov/Kconfig b/kernel/gcov/Kconfig
index 58f87a3092f3..19facd4289cd 100644
--- a/kernel/gcov/Kconfig
+++ b/kernel/gcov/Kconfig
@@ -5,6 +5,7 @@ config GCOV_KERNEL
 	bool "Enable gcov-based kernel profiling"
 	depends on DEBUG_FS
 	depends on !CC_IS_CLANG || CLANG_VERSION >= 110000
+	depends on !X86 || (X86 && CC_HAS_NO_PROFILE_FN_ATTR)
 	select CONSTRUCTORS
 	default n
 	help
diff --git a/kernel/pgo/Kconfig b/kernel/pgo/Kconfig
index d2053df1111c..26f75ac4c6c1 100644
--- a/kernel/pgo/Kconfig
+++ b/kernel/pgo/Kconfig
@@ -8,7 +8,8 @@ config PGO_CLANG
 	bool "Enable clang's PGO-based kernel profiling"
 	depends on DEBUG_FS
 	depends on ARCH_SUPPORTS_PGO_CLANG
-	depends on CC_IS_CLANG && CLANG_VERSION >= 120000
+	depends on CC_IS_CLANG
+	depends on CC_HAS_NO_PROFILE_FN_ATTR
 	help
 	  This option enables clang's PGO (Profile Guided Optimization) based
 	  code profiling to better optimize the kernel.
-- 
2.32.0.288.g62a8d224e6-goog