On Mon, Jun 21, 2021 at 11:50 AM Bill Wendling <morbo@xxxxxxxxxx> wrote: > > On Mon, Jun 21, 2021 at 11:22 AM Nick Desaulniers > <ndesaulniers@xxxxxxxxxx> wrote: > > > > On Fri, Jun 18, 2021 at 11:23 PM Marco Elver <elver@xxxxxxxxxx> wrote: > > > > > > On Sat, 19 Jun 2021 at 01:30, Nick Desaulniers <ndesaulniers@xxxxxxxxxx> wrote: > > > > > > > > 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@xxxxxxxxxx> > > > > Cc: Peter Oberparleiter <oberpar@xxxxxxxxxxxxx> > > > > Link: https://lore.kernel.org/lkml/YMTn9yjuemKFLbws@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/ > > > > Link: https://lore.kernel.org/lkml/YMcssV%2Fn5IBGv4f0@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/ > > > > Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx> > > > > Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> > > > > --- > > > > 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) > > > > > > [+Cc Mark] > > > > > > arm64 is also starting to rely on noinstr working properly. > > > > Sure, > > Will, Catalin, other arm64 folks: > > Any thoughts on requiring GCC 7.1+/Clang 13.0+ for GCOV support? That > > way we can better guarantee that GCOV (and eventually, PGO) don't > > touch noinstr functions? > > > > If that's ok, I'll add modify the above like: > > > > + depends on !ARM64 || (ARM64 && CC_HAS_NO_PROFILE_FN_ATTR) > > > Wouldn't "!ARM64 || CC_HAS_NO_PROFILE_FN_ATTR" be more succinct? We need to be able to express via Kconfig "GCOV should not be enabled for architectures that use noinstr when the toolchain does not support __attribute__((no_profile_instrument_function))." Where "architectures that use noinstr" are currently arm64, s390, and x86. So I guess we could do: + depends on !ARM64 || !S390 || !X86 || CC_HAS_NO_PROFILE_FN_ATTR (We could add a Kconfig for ARCH_WANTS_NO_INSTR, which might be more informative than listed out architectures which might be non-obvious to passers-by). It would be most succinct to raise the requirements to: "GCOV should not be enabled when the toolchain does not support __attribute__((no_profile_instrument_function))." Then we could do: + depends on CC_HAS_NO_PROFILE_FN_ATTR Assuming no one has the requirement to support GCOV on PPC with GCC < 7.1, for example. > > > to the above hunk in v2. Oh, looks like arch/s390 also uses noinstr. > > Same question applies then: > > > > + depends on !S390 || (S390 && CC_HAS_NO_PROFILE_FN_ATTR) > > > > Or, we could just do > > > > + depends on CC_HAS_NO_PROFILE_FN_ATTR > > > > Though that will penalize architectures not using noinstr, that still > > would like to use GCOV with versions of GCC older than 7.1. Perhaps > > there are no such such users, or they should consider upgrading their > > tools to we can stick with the simpler Kconfig? Thoughts? > > > > > > > > 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@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx > > > > > > 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. > > > > > > > > > > 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 > > > > > > > > > > > > -- > > Thanks, > > ~Nick Desaulniers -- Thanks, ~Nick Desaulniers
