Re: [PATCH 2/2] Kconfig: CC_HAS_NO_PROFILE_FN_ATTR, depend on for GCOV and PGO
From: Marco Elver <elver@google.com>
Date: 2021-06-19 06:23:52
Also in:
linux-kbuild, linux-toolchains, lkml
On Sat, 19 Jun 2021 at 01:30, Nick Desaulniers [off-list ref] wrote:
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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@kernel.org> Cc: Peter Oberparleiter <oberpar@linux.ibm.com> Link: https://lore.kernel.org/lkml/YMTn9yjuemKFLbws@hirez.programming.kicks-ass.net/ (local) Link: https://lore.kernel.org/lkml/YMcssV%2Fn5IBGv4f0@hirez.programming.kicks-ass.net/ (local) Suggested-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Nick Desaulniers <redacted> --- 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 booldiff --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)
[+Cc Mark] arm64 is also starting to rely on noinstr working properly. This should probably be a 'select ARCH_HAS_GCOV_PROFILE_ALL if CC_HAS_NO_PROFILE_FN_ATTR' in the relevant arch/../Kconfig. Alternatively, using: https://lkml.kernel.org/r/YMcssV/n5IBGv4f0@hirez.programming.kicks-ass.net But I'd probably not overcomplicate things at this point and just use ARCH_HAS_GCOV_PROFILE_ALL, because GCOV seems to be a) rarely used, and b) if someone decides to selectively instrument stuff like entry code, we can just say it's user error.
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select CONSTRUCTORS default n helpdiff --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