2021-06-19 09:45:51

by Marco Elver

Subject: Re: [PATCH 2/2] Kconfig: CC_HAS_NO_PROFILE_FN_ATTR, depend on for GCOV and PGO

On Sat, 19 Jun 2021 at 01:30, Nick Desaulniers <[email protected]> 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 <[email protected]>
> Cc: Peter Oberparleiter <[email protected]>
> Link: https://lore.kernel.org/lkml/[email protected]/
> Link: https://lore.kernel.org/lkml/YMcssV%[email protected]/
> Suggested-by: Peter Zijlstra <[email protected]>
> Signed-off-by: Nick Desaulniers <[email protected]>
> ---
> 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.

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/[email protected]

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
>

2021-06-21 18:24:24

by Nick Desaulniers

Subject: Re: [PATCH 2/2] Kconfig: CC_HAS_NO_PROFILE_FN_ATTR, depend on for GCOV and PGO

On Fri, Jun 18, 2021 at 11:23 PM Marco Elver <[email protected]> wrote:
>
> On Sat, 19 Jun 2021 at 01:30, Nick Desaulniers <[email protected]> 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 <[email protected]>
> > Cc: Peter Oberparleiter <[email protected]>
> > Link: https://lore.kernel.org/lkml/[email protected]/
> > Link: https://lore.kernel.org/lkml/YMcssV%[email protected]/
> > Suggested-by: Peter Zijlstra <[email protected]>
> > Signed-off-by: Nick Desaulniers <[email protected]>
> > ---
> > 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)

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/[email protected]
>
> 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

2021-06-21 18:54:15

by Bill Wendling

Subject: Re: [PATCH 2/2] Kconfig: CC_HAS_NO_PROFILE_FN_ATTR, depend on for GCOV and PGO

On Mon, Jun 21, 2021 at 11:22 AM Nick Desaulniers
<[email protected]> wrote:
>
> On Fri, Jun 18, 2021 at 11:23 PM Marco Elver <[email protected]> wrote:
> >
> > On Sat, 19 Jun 2021 at 01:30, Nick Desaulniers <[email protected]> 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 <[email protected]>
> > > Cc: Peter Oberparleiter <[email protected]>
> > > Link: https://lore.kernel.org/lkml/[email protected]/
> > > Link: https://lore.kernel.org/lkml/YMcssV%[email protected]/
> > > Suggested-by: Peter Zijlstra <[email protected]>
> > > Signed-off-by: Nick Desaulniers <[email protected]>
> > > ---
> > > 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?

> 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/[email protected]
> >
> > 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

2021-06-21 20:47:52

by Nick Desaulniers

Subject: Re: [PATCH 2/2] Kconfig: CC_HAS_NO_PROFILE_FN_ATTR, depend on for GCOV and PGO

On Mon, Jun 21, 2021 at 11:50 AM Bill Wendling <[email protected]> wrote:
>
> On Mon, Jun 21, 2021 at 11:22 AM Nick Desaulniers
> <[email protected]> wrote:
> >
> > On Fri, Jun 18, 2021 at 11:23 PM Marco Elver <[email protected]> wrote:
> > >
> > > On Sat, 19 Jun 2021 at 01:30, Nick Desaulniers <[email protected]> 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 <[email protected]>
> > > > Cc: Peter Oberparleiter <[email protected]>
> > > > Link: https://lore.kernel.org/lkml/[email protected]/
> > > > Link: https://lore.kernel.org/lkml/YMcssV%[email protected]/
> > > > Suggested-by: Peter Zijlstra <[email protected]>
> > > > Signed-off-by: Nick Desaulniers <[email protected]>
> > > > ---
> > > > 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/[email protected]
> > >
> > > 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

2021-06-21 21:17:01

by Nathan Chancellor

Subject: Re: [PATCH 2/2] Kconfig: CC_HAS_NO_PROFILE_FN_ATTR, depend on for GCOV and PGO

On 6/21/2021 1:43 PM, Nick Desaulniers wrote:
> On Mon, Jun 21, 2021 at 11:50 AM Bill Wendling <[email protected]> wrote:
>>
>> On Mon, Jun 21, 2021 at 11:22 AM Nick Desaulniers
>> <[email protected]> wrote:
>>>
>>> On Fri, Jun 18, 2021 at 11:23 PM Marco Elver <[email protected]> wrote:
>>>>
>>>> On Sat, 19 Jun 2021 at 01:30, Nick Desaulniers <[email protected]> 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 <[email protected]>
>>>>> Cc: Peter Oberparleiter <[email protected]>
>>>>> Link: https://lore.kernel.org/lkml/[email protected]/
>>>>> Link: https://lore.kernel.org/lkml/YMcssV%[email protected]/
>>>>> Suggested-by: Peter Zijlstra <[email protected]>
>>>>> Signed-off-by: Nick Desaulniers <[email protected]>
>>>>> ---
>>>>> 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).

I agree that spelling this out might be nicer for the future, in case
instances like this crop up again. ARCH_REQUIRES_NO_INSTR might be a
better wording?

> 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

Then this could become

depends on !ARCH_REQUIRES_NO_INSTR || (ARCH_REQUIRES_NO_INSTR &&
CC_HAS_NO_PROFILE_FN_ATTR)

(sorry for the potential wrap).

Cheers,
Nathan

> 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/[email protected]
>>>>
>>>> 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
>
>
>

2021-06-22 09:28:55

by Catalin Marinas

Subject: Re: [PATCH 2/2] Kconfig: CC_HAS_NO_PROFILE_FN_ATTR, depend on for GCOV and PGO

On Mon, Jun 21, 2021 at 01:43:54PM -0700, Nick Desaulniers wrote:
> On Mon, Jun 21, 2021 at 11:50 AM Bill Wendling <[email protected]> wrote:
> > On Mon, Jun 21, 2021 at 11:22 AM Nick Desaulniers
> > <[email protected]> wrote:
> > > On Fri, Jun 18, 2021 at 11:23 PM Marco Elver <[email protected]> wrote:
> > > > On Sat, 19 Jun 2021 at 01:30, Nick Desaulniers <[email protected]> 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 <[email protected]>
> > > > > Cc: Peter Oberparleiter <[email protected]>
> > > > > Link: https://lore.kernel.org/lkml/[email protected]/
> > > > > Link: https://lore.kernel.org/lkml/YMcssV%[email protected]/
> > > > > Suggested-by: Peter Zijlstra <[email protected]>
> > > > > Signed-off-by: Nick Desaulniers <[email protected]>
> > > > > ---
> > > > > 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

I think you want:

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).

That would probably look better.

--
Catalin

2021-06-22 09:32:02

by Mark Rutland

Subject: Re: [PATCH 2/2] Kconfig: CC_HAS_NO_PROFILE_FN_ATTR, depend on for GCOV and PGO

On Tue, Jun 22, 2021 at 10:25:34AM +0100, Catalin Marinas wrote:
> On Mon, Jun 21, 2021 at 01:43:54PM -0700, Nick Desaulniers wrote:
> > 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
>
> I think you want:
>
> 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).
>
> That would probably look better.

It does; see:

https://lore.kernel.org/r/[email protected]

:)

Thanks,
Mark.

2021-06-22 09:34:16

by Catalin Marinas

Subject: Re: [PATCH 2/2] Kconfig: CC_HAS_NO_PROFILE_FN_ATTR, depend on for GCOV and PGO

On Tue, Jun 22, 2021 at 10:29:37AM +0100, Mark Rutland wrote:
> On Tue, Jun 22, 2021 at 10:25:34AM +0100, Catalin Marinas wrote:
> > On Mon, Jun 21, 2021 at 01:43:54PM -0700, Nick Desaulniers wrote:
> > > 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
> >
> > I think you want:
> >
> > 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).
> >
> > That would probably look better.
>
> It does; see:
>
> https://lore.kernel.org/r/[email protected]

I'm getting there, eventually ;).

--
Catalin