[PATCH 1/2] kcsan: xtensa: Add atomic builtin stubs for 32-bit systems

[PATCH 1/2] kcsan: xtensa: Add atomic builtin stubs for 32-bit systems

[Rohan McLure]

KCSAN instruments calls to atomic builtins, and will in turn call these
builtins itself. As such, architectures supporting KCSAN must have
compiler support for these atomic primitives.

Since 32-bit systems are unlikely to have 64-bit compiler builtins,
provide a stub for each missing builtin, and use BUG() to assert
unreachability.

In commit 725aea873261 ("xtensa: enable KCSAN"), xtensa implements these
locally. Move these definitions to be accessible to all 32-bit
architectures that do not provide the necessary builtins, with opt in
for PowerPC and xtensa.

Signed-off-by: Rohan McLure <rmclure@linux.ibm.com>
Reviewed-by: Max Filippov <jcmvbkbc@gmail.com>
---
Previously issued as a part of a patch series adding KCSAN support to
64-bit.
Link: https://lore.kernel.org/linuxppc-dev/167646486000.1421441.10070059569986228558.b4-ty@ellerman.id.au/T/#t
v1: Remove __has_builtin check, as gcc is not obligated to inline
builtins detected using this check, but instead is permitted to supply
them in libatomic:
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108734
Instead, opt-in PPC32 and xtensa.
---
 arch/xtensa/lib/Makefile                              | 1 -
 kernel/kcsan/Makefile                                 | 2 ++
 arch/xtensa/lib/kcsan-stubs.c => kernel/kcsan/stubs.c | 0
 3 files changed, 2 insertions(+), 1 deletion(-)
 rename arch/xtensa/lib/kcsan-stubs.c => kernel/kcsan/stubs.c (100%)

diff --git a/arch/xtensa/lib/Makefile b/arch/xtensa/lib/Makefile
index 7ecef0519a27..d69356dc97df 100644
--- a/arch/xtensa/lib/Makefile
+++ b/arch/xtensa/lib/Makefile
@@ -8,5 +8,4 @@ lib-y	+= memcopy.o memset.o checksum.o \
 	   divsi3.o udivsi3.o modsi3.o umodsi3.o mulsi3.o umulsidi3.o \
 	   usercopy.o strncpy_user.o strnlen_user.o
 lib-$(CONFIG_PCI) += pci-auto.o
-lib-$(CONFIG_KCSAN) += kcsan-stubs.o
 KCSAN_SANITIZE_kcsan-stubs.o := n
diff --git a/kernel/kcsan/Makefile b/kernel/kcsan/Makefile
index 8cf70f068d92..86dd713d8855 100644
--- a/kernel/kcsan/Makefile
+++ b/kernel/kcsan/Makefile
@@ -12,6 +12,8 @@ CFLAGS_core.o := $(call cc-option,-fno-conserve-stack) \
 	-fno-stack-protector -DDISABLE_BRANCH_PROFILING
 
 obj-y := core.o debugfs.o report.o
+obj-$(CONFIG_PPC32) += stubs.o
+obj-$(CONFIG_XTENSA) += stubs.o
 
 KCSAN_INSTRUMENT_BARRIERS_selftest.o := y
 obj-$(CONFIG_KCSAN_SELFTEST) += selftest.o
diff --git a/arch/xtensa/lib/kcsan-stubs.c b/kernel/kcsan/stubs.c
similarity index 100%
rename from arch/xtensa/lib/kcsan-stubs.c
rename to kernel/kcsan/stubs.c
-- 
2.37.2

[PATCH 2/2] powerpc/{32,book3e}: kcsan: Extend KCSAN Support

[Rohan McLure]

Enable HAVE_ARCH_KCSAN on all powerpc platforms, permitting use of the
kernel concurrency sanitiser through the CONFIG_KCSAN_* kconfig options.

Boots and passes selftests on 32-bit and 64-bit platforms. See
documentation in Documentation/dev-tools/kcsan.rst for more information.

Signed-off-by: Rohan McLure <rmclure@linux.ibm.com>
---
New patch
---
 arch/powerpc/Kconfig | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 2c9cdf1d8761..45771448d47a 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -197,7 +197,7 @@ config PPC
 	select HAVE_ARCH_KASAN			if PPC_RADIX_MMU
 	select HAVE_ARCH_KASAN			if PPC_BOOK3E_64
 	select HAVE_ARCH_KASAN_VMALLOC		if HAVE_ARCH_KASAN
-	select HAVE_ARCH_KCSAN            	if PPC_BOOK3S_64
+	select HAVE_ARCH_KCSAN
 	select HAVE_ARCH_KFENCE			if ARCH_SUPPORTS_DEBUG_PAGEALLOC
 	select HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET
 	select HAVE_ARCH_KGDB
-- 
2.37.2

Re: [PATCH 2/2] powerpc/{32,book3e}: kcsan: Extend KCSAN Support

[Christophe Leroy]

Le 16/02/2023 à 06:09, Rohan McLure a écrit :
> Enable HAVE_ARCH_KCSAN on all powerpc platforms, permitting use of the
> kernel concurrency sanitiser through the CONFIG_KCSAN_* kconfig options.
> 
> Boots and passes selftests on 32-bit and 64-bit platforms. See
> documentation in Documentation/dev-tools/kcsan.rst for more information.
> 
> Signed-off-by: Rohan McLure <rmclure@linux.ibm.com>
> ---
> New patch
> ---
>   arch/powerpc/Kconfig | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 2c9cdf1d8761..45771448d47a 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -197,7 +197,7 @@ config PPC
>   	select HAVE_ARCH_KASAN			if PPC_RADIX_MMU
>   	select HAVE_ARCH_KASAN			if PPC_BOOK3E_64
>   	select HAVE_ARCH_KASAN_VMALLOC		if HAVE_ARCH_KASAN
> -	select HAVE_ARCH_KCSAN            	if PPC_BOOK3S_64
> +	select HAVE_ARCH_KCSAN

So that's a followup of a not yet posted version v5 of the other series ?
Why not just add patch 1 in that series and have KCSAN for all powerpc 
at once ?

>   	select HAVE_ARCH_KFENCE			if ARCH_SUPPORTS_DEBUG_PAGEALLOC
>   	select HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET
>   	select HAVE_ARCH_KGDB

Re: [PATCH 2/2] powerpc/{32,book3e}: kcsan: Extend KCSAN Support

[Rohan McLure]

> On 16 Feb 2023, at 6:14 pm, Christophe Leroy <christophe.leroy@csgroup.eu> wrote:
> 
> 
> 
> Le 16/02/2023 à 06:09, Rohan McLure a écrit :
>> Enable HAVE_ARCH_KCSAN on all powerpc platforms, permitting use of the
>> kernel concurrency sanitiser through the CONFIG_KCSAN_* kconfig options.
>> 
>> Boots and passes selftests on 32-bit and 64-bit platforms. See
>> documentation in Documentation/dev-tools/kcsan.rst for more information.
>> 
>> Signed-off-by: Rohan McLure <rmclure@linux.ibm.com>
>> ---
>> New patch
>> ---
>>  arch/powerpc/Kconfig | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
>> index 2c9cdf1d8761..45771448d47a 100644
>> --- a/arch/powerpc/Kconfig
>> +++ b/arch/powerpc/Kconfig
>> @@ -197,7 +197,7 @@ config PPC
>>   select HAVE_ARCH_KASAN if PPC_RADIX_MMU
>>   select HAVE_ARCH_KASAN if PPC_BOOK3E_64
>>   select HAVE_ARCH_KASAN_VMALLOC if HAVE_ARCH_KASAN
>> - select HAVE_ARCH_KCSAN             if PPC_BOOK3S_64
>> + select HAVE_ARCH_KCSAN
> 
> So that's a followup of a not yet posted version v5 of the other series ?
> Why not just add patch 1 in that series and have KCSAN for all powerpc 
> at once ?

So the v3 was accepted upstream, likely to appear in 6.3. This patch series is
just to extend support to other platforms, once kcsan supports us.

Link: https://patchwork.ozlabs.org/project/linuxppc-dev/cover/20230206021801.105268-1-rmclure@linux.ibm.com/

> 
>>   select HAVE_ARCH_KFENCE if ARCH_SUPPORTS_DEBUG_PAGEALLOC
>>   select HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET
>>   select HAVE_ARCH_KGDB

Re: [PATCH 2/2] powerpc/{32,book3e}: kcsan: Extend KCSAN Support

[Christophe Leroy]

Le 17/02/2023 à 00:23, Rohan McLure a écrit :
>> On 16 Feb 2023, at 6:14 pm, Christophe Leroy <christophe.leroy@csgroup.eu> wrote:
>>
>>
>>
>> Le 16/02/2023 à 06:09, Rohan McLure a écrit :
>>> Enable HAVE_ARCH_KCSAN on all powerpc platforms, permitting use of the
>>> kernel concurrency sanitiser through the CONFIG_KCSAN_* kconfig options.
>>>
>>> Boots and passes selftests on 32-bit and 64-bit platforms. See
>>> documentation in Documentation/dev-tools/kcsan.rst for more information.
>>>
>>> Signed-off-by: Rohan McLure <rmclure@linux.ibm.com>
>>> ---
>>> New patch
>>> ---
>>>   arch/powerpc/Kconfig | 2 +-
>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
>>> index 2c9cdf1d8761..45771448d47a 100644
>>> --- a/arch/powerpc/Kconfig
>>> +++ b/arch/powerpc/Kconfig
>>> @@ -197,7 +197,7 @@ config PPC
>>>    select HAVE_ARCH_KASAN if PPC_RADIX_MMU
>>>    select HAVE_ARCH_KASAN if PPC_BOOK3E_64
>>>    select HAVE_ARCH_KASAN_VMALLOC if HAVE_ARCH_KASAN
>>> - select HAVE_ARCH_KCSAN             if PPC_BOOK3S_64
>>> + select HAVE_ARCH_KCSAN
>>
>> So that's a followup of a not yet posted version v5 of the other series ?
>> Why not just add patch 1 in that series and have KCSAN for all powerpc
>> at once ?
> 
> So the v3 was accepted upstream, likely to appear in 6.3. This patch series is
> just to extend support to other platforms, once kcsan supports us.

Hum ... Ok.

I checked in checkpatch before writting that mail and saw that v4 was 
flagged "changes requested", so I didn't notice v3 was accepted.



> 
> Link: https://patchwork.ozlabs.org/project/linuxppc-dev/cover/20230206021801.105268-1-rmclure@linux.ibm.com/
> 
>>
>>>    select HAVE_ARCH_KFENCE if ARCH_SUPPORTS_DEBUG_PAGEALLOC
>>>    select HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET
>>>    select HAVE_ARCH_KGDB
> 
> 

Re: [PATCH 2/2] powerpc/{32,book3e}: kcsan: Extend KCSAN Support

[Michael Ellerman]

Christophe Leroy <christophe.leroy@csgroup.eu> writes:
> Le 17/02/2023 à 00:23, Rohan McLure a écrit :
>>> On 16 Feb 2023, at 6:14 pm, Christophe Leroy <christophe.leroy@csgroup.eu> wrote:
>>> Le 16/02/2023 à 06:09, Rohan McLure a écrit :
>>>> Enable HAVE_ARCH_KCSAN on all powerpc platforms, permitting use of the
>>>> kernel concurrency sanitiser through the CONFIG_KCSAN_* kconfig options.
>>>>
>>>> Boots and passes selftests on 32-bit and 64-bit platforms. See
>>>> documentation in Documentation/dev-tools/kcsan.rst for more information.
>>>>
>>>> Signed-off-by: Rohan McLure <rmclure@linux.ibm.com>
>>>> ---
>>>> New patch
>>>> ---
>>>>   arch/powerpc/Kconfig | 2 +-
>>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
>>>> index 2c9cdf1d8761..45771448d47a 100644
>>>> --- a/arch/powerpc/Kconfig
>>>> +++ b/arch/powerpc/Kconfig
>>>> @@ -197,7 +197,7 @@ config PPC
>>>>    select HAVE_ARCH_KASAN if PPC_RADIX_MMU
>>>>    select HAVE_ARCH_KASAN if PPC_BOOK3E_64
>>>>    select HAVE_ARCH_KASAN_VMALLOC if HAVE_ARCH_KASAN
>>>> - select HAVE_ARCH_KCSAN             if PPC_BOOK3S_64
>>>> + select HAVE_ARCH_KCSAN
>>>
>>> So that's a followup of a not yet posted version v5 of the other series ?
>>> Why not just add patch 1 in that series and have KCSAN for all powerpc
>>> at once ?
>> 
>> So the v3 was accepted upstream, likely to appear in 6.3. This patch series is
>> just to extend support to other platforms, once kcsan supports us.
>
> Hum ... Ok.
>
> I checked in checkpatch before writting that mail and saw that v4 was 
> flagged "changes requested", so I didn't notice v3 was accepted.

Sorry that's my fault. I talked to Rohan on chat and decided that taking
v3 was the best way to get something in before the merge window closed.

cheers

Re: [PATCH 1/2] kcsan: xtensa: Add atomic builtin stubs for 32-bit systems

[Christophe Leroy]

Le 16/02/2023 à 06:09, Rohan McLure a écrit :
> KCSAN instruments calls to atomic builtins, and will in turn call these
> builtins itself. As such, architectures supporting KCSAN must have
> compiler support for these atomic primitives.
> 
> Since 32-bit systems are unlikely to have 64-bit compiler builtins,
> provide a stub for each missing builtin, and use BUG() to assert
> unreachability.
> 
> In commit 725aea873261 ("xtensa: enable KCSAN"), xtensa implements these
> locally. Move these definitions to be accessible to all 32-bit
> architectures that do not provide the necessary builtins, with opt in
> for PowerPC and xtensa.
> 
> Signed-off-by: Rohan McLure <rmclure@linux.ibm.com>
> Reviewed-by: Max Filippov <jcmvbkbc@gmail.com>

This series should also be addressed to KCSAN Maintainers, shouldn't it ?

KCSAN
M:	Marco Elver <elver@google.com>
R:	Dmitry Vyukov <dvyukov@google.com>
L:	kasan-dev@googlegroups.com
S:	Maintained
F:	Documentation/dev-tools/kcsan.rst
F:	include/linux/kcsan*.h
F:	kernel/kcsan/
F:	lib/Kconfig.kcsan
F:	scripts/Makefile.kcsan


> ---
> Previously issued as a part of a patch series adding KCSAN support to
> 64-bit.
> Link: https://lore.kernel.org/linuxppc-dev/167646486000.1421441.10070059569986228558.b4-ty@ellerman.id.au/T/#t
> v1: Remove __has_builtin check, as gcc is not obligated to inline
> builtins detected using this check, but instead is permitted to supply
> them in libatomic:
> Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108734
> Instead, opt-in PPC32 and xtensa.
> ---
>   arch/xtensa/lib/Makefile                              | 1 -
>   kernel/kcsan/Makefile                                 | 2 ++
>   arch/xtensa/lib/kcsan-stubs.c => kernel/kcsan/stubs.c | 0
>   3 files changed, 2 insertions(+), 1 deletion(-)
>   rename arch/xtensa/lib/kcsan-stubs.c => kernel/kcsan/stubs.c (100%)
> 
> diff --git a/arch/xtensa/lib/Makefile b/arch/xtensa/lib/Makefile
> index 7ecef0519a27..d69356dc97df 100644
> --- a/arch/xtensa/lib/Makefile
> +++ b/arch/xtensa/lib/Makefile
> @@ -8,5 +8,4 @@ lib-y	+= memcopy.o memset.o checksum.o \
>   	   divsi3.o udivsi3.o modsi3.o umodsi3.o mulsi3.o umulsidi3.o \
>   	   usercopy.o strncpy_user.o strnlen_user.o
>   lib-$(CONFIG_PCI) += pci-auto.o
> -lib-$(CONFIG_KCSAN) += kcsan-stubs.o
>   KCSAN_SANITIZE_kcsan-stubs.o := n
> diff --git a/kernel/kcsan/Makefile b/kernel/kcsan/Makefile
> index 8cf70f068d92..86dd713d8855 100644
> --- a/kernel/kcsan/Makefile
> +++ b/kernel/kcsan/Makefile
> @@ -12,6 +12,8 @@ CFLAGS_core.o := $(call cc-option,-fno-conserve-stack) \
>   	-fno-stack-protector -DDISABLE_BRANCH_PROFILING
>   
>   obj-y := core.o debugfs.o report.o
> +obj-$(CONFIG_PPC32) += stubs.o
> +obj-$(CONFIG_XTENSA) += stubs.o

Not sure it is acceptable to do it that way.

There should likely be something like a CONFIG_ARCH_WANTS_KCSAN_STUBS in 
KCSAN's Kconfig then PPC32 and XTENSA should select it.

>   
>   KCSAN_INSTRUMENT_BARRIERS_selftest.o := y
>   obj-$(CONFIG_KCSAN_SELFTEST) += selftest.o
> diff --git a/arch/xtensa/lib/kcsan-stubs.c b/kernel/kcsan/stubs.c
> similarity index 100%
> rename from arch/xtensa/lib/kcsan-stubs.c
> rename to kernel/kcsan/stubs.c

Re: [PATCH 1/2] kcsan: xtensa: Add atomic builtin stubs for 32-bit systems

[Marco Elver]

On Thu, Feb 16, 2023 at 07:12AM +0000, Christophe Leroy wrote:
> 
> 
> Le 16/02/2023 à 06:09, Rohan McLure a écrit :
> > KCSAN instruments calls to atomic builtins, and will in turn call these
> > builtins itself. As such, architectures supporting KCSAN must have
> > compiler support for these atomic primitives.
> > 
> > Since 32-bit systems are unlikely to have 64-bit compiler builtins,
> > provide a stub for each missing builtin, and use BUG() to assert
> > unreachability.
> > 
> > In commit 725aea873261 ("xtensa: enable KCSAN"), xtensa implements these
> > locally. Move these definitions to be accessible to all 32-bit
> > architectures that do not provide the necessary builtins, with opt in
> > for PowerPC and xtensa.
> > 
> > Signed-off-by: Rohan McLure <rmclure@linux.ibm.com>
> > Reviewed-by: Max Filippov <jcmvbkbc@gmail.com>
> 
> This series should also be addressed to KCSAN Maintainers, shouldn't it ?
> 
> KCSAN
> M:	Marco Elver <elver@google.com>
> R:	Dmitry Vyukov <dvyukov@google.com>
> L:	kasan-dev@googlegroups.com
> S:	Maintained
> F:	Documentation/dev-tools/kcsan.rst
> F:	include/linux/kcsan*.h
> F:	kernel/kcsan/
> F:	lib/Kconfig.kcsan
> F:	scripts/Makefile.kcsan
> 
> 
> > ---
> > Previously issued as a part of a patch series adding KCSAN support to
> > 64-bit.
> > Link: https://lore.kernel.org/linuxppc-dev/167646486000.1421441.10070059569986228558.b4-ty@ellerman.id.au/T/#t
> > v1: Remove __has_builtin check, as gcc is not obligated to inline
> > builtins detected using this check, but instead is permitted to supply
> > them in libatomic:
> > Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108734
> > Instead, opt-in PPC32 and xtensa.
> > ---
> >   arch/xtensa/lib/Makefile                              | 1 -
> >   kernel/kcsan/Makefile                                 | 2 ++
> >   arch/xtensa/lib/kcsan-stubs.c => kernel/kcsan/stubs.c | 0
> >   3 files changed, 2 insertions(+), 1 deletion(-)
> >   rename arch/xtensa/lib/kcsan-stubs.c => kernel/kcsan/stubs.c (100%)
> > 
> > diff --git a/arch/xtensa/lib/Makefile b/arch/xtensa/lib/Makefile
> > index 7ecef0519a27..d69356dc97df 100644
> > --- a/arch/xtensa/lib/Makefile
> > +++ b/arch/xtensa/lib/Makefile
> > @@ -8,5 +8,4 @@ lib-y	+= memcopy.o memset.o checksum.o \
> >   	   divsi3.o udivsi3.o modsi3.o umodsi3.o mulsi3.o umulsidi3.o \
> >   	   usercopy.o strncpy_user.o strnlen_user.o
> >   lib-$(CONFIG_PCI) += pci-auto.o
> > -lib-$(CONFIG_KCSAN) += kcsan-stubs.o
> >   KCSAN_SANITIZE_kcsan-stubs.o := n
> > diff --git a/kernel/kcsan/Makefile b/kernel/kcsan/Makefile
> > index 8cf70f068d92..86dd713d8855 100644
> > --- a/kernel/kcsan/Makefile
> > +++ b/kernel/kcsan/Makefile
> > @@ -12,6 +12,8 @@ CFLAGS_core.o := $(call cc-option,-fno-conserve-stack) \
> >   	-fno-stack-protector -DDISABLE_BRANCH_PROFILING
> >   
> >   obj-y := core.o debugfs.o report.o
> > +obj-$(CONFIG_PPC32) += stubs.o
> > +obj-$(CONFIG_XTENSA) += stubs.o
> 
> Not sure it is acceptable to do it that way.
> 
> There should likely be something like a CONFIG_ARCH_WANTS_KCSAN_STUBS in 
> KCSAN's Kconfig then PPC32 and XTENSA should select it.

The longer I think about it, since these stubs all BUG() anyway, perhaps
we ought to just avoid them altogether. If you delete all the stubs from
ppc and xtensa, but do this:

 | diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c
 | index 54d077e1a2dc..8169d6dadd0e 100644
 | --- a/kernel/kcsan/core.c
 | +++ b/kernel/kcsan/core.c
 | @@ -1261,7 +1261,9 @@ static __always_inline void kcsan_atomic_builtin_memorder(int memorder)
 |  DEFINE_TSAN_ATOMIC_OPS(8);
 |  DEFINE_TSAN_ATOMIC_OPS(16);
 |  DEFINE_TSAN_ATOMIC_OPS(32);
 | +#ifdef CONFIG_64BIT
 |  DEFINE_TSAN_ATOMIC_OPS(64);
 | +#endif
 |  
 |  void __tsan_atomic_thread_fence(int memorder);
 |  void __tsan_atomic_thread_fence(int memorder)

Does that work?

Re: [PATCH 1/2] kcsan: xtensa: Add atomic builtin stubs for 32-bit systems

[Rohan McLure]

> On 16 Feb 2023, at 7:09 pm, Marco Elver <elver@google.com> wrote:
> 
> On Thu, Feb 16, 2023 at 07:12AM +0000, Christophe Leroy wrote:
>> 
>> 
>> Le 16/02/2023 à 06:09, Rohan McLure a écrit :
>>> KCSAN instruments calls to atomic builtins, and will in turn call these
>>> builtins itself. As such, architectures supporting KCSAN must have
>>> compiler support for these atomic primitives.
>>> 
>>> Since 32-bit systems are unlikely to have 64-bit compiler builtins,
>>> provide a stub for each missing builtin, and use BUG() to assert
>>> unreachability.
>>> 
>>> In commit 725aea873261 ("xtensa: enable KCSAN"), xtensa implements these
>>> locally. Move these definitions to be accessible to all 32-bit
>>> architectures that do not provide the necessary builtins, with opt in
>>> for PowerPC and xtensa.
>>> 
>>> Signed-off-by: Rohan McLure <rmclure@linux.ibm.com>
>>> Reviewed-by: Max Filippov <jcmvbkbc@gmail.com>
>> 
>> This series should also be addressed to KCSAN Maintainers, shouldn't it ?
>> 
>> KCSAN
>> M: Marco Elver <elver@google.com>
>> R: Dmitry Vyukov <dvyukov@google.com>
>> L: kasan-dev@googlegroups.com
>> S: Maintained
>> F: Documentation/dev-tools/kcsan.rst
>> F: include/linux/kcsan*.h
>> F: kernel/kcsan/
>> F: lib/Kconfig.kcsan
>> F: scripts/Makefile.kcsan
>> 
>> 
>>> ---
>>> Previously issued as a part of a patch series adding KCSAN support to
>>> 64-bit.
>>> Link: https://lore.kernel.org/linuxppc-dev/167646486000.1421441.10070059569986228558.b4-ty@ellerman.id.au/T/#t
>>> v1: Remove __has_builtin check, as gcc is not obligated to inline
>>> builtins detected using this check, but instead is permitted to supply
>>> them in libatomic:
>>> Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108734
>>> Instead, opt-in PPC32 and xtensa.
>>> ---
>>>  arch/xtensa/lib/Makefile                              | 1 -
>>>  kernel/kcsan/Makefile                                 | 2 ++
>>>  arch/xtensa/lib/kcsan-stubs.c => kernel/kcsan/stubs.c | 0
>>>  3 files changed, 2 insertions(+), 1 deletion(-)
>>>  rename arch/xtensa/lib/kcsan-stubs.c => kernel/kcsan/stubs.c (100%)
>>> 
>>> diff --git a/arch/xtensa/lib/Makefile b/arch/xtensa/lib/Makefile
>>> index 7ecef0519a27..d69356dc97df 100644
>>> --- a/arch/xtensa/lib/Makefile
>>> +++ b/arch/xtensa/lib/Makefile
>>> @@ -8,5 +8,4 @@ lib-y += memcopy.o memset.o checksum.o \
>>>      divsi3.o udivsi3.o modsi3.o umodsi3.o mulsi3.o umulsidi3.o \
>>>      usercopy.o strncpy_user.o strnlen_user.o
>>>  lib-$(CONFIG_PCI) += pci-auto.o
>>> -lib-$(CONFIG_KCSAN) += kcsan-stubs.o
>>>  KCSAN_SANITIZE_kcsan-stubs.o := n
>>> diff --git a/kernel/kcsan/Makefile b/kernel/kcsan/Makefile
>>> index 8cf70f068d92..86dd713d8855 100644
>>> --- a/kernel/kcsan/Makefile
>>> +++ b/kernel/kcsan/Makefile
>>> @@ -12,6 +12,8 @@ CFLAGS_core.o := $(call cc-option,-fno-conserve-stack) \
>>>   -fno-stack-protector -DDISABLE_BRANCH_PROFILING
>>> 
>>>  obj-y := core.o debugfs.o report.o
>>> +obj-$(CONFIG_PPC32) += stubs.o
>>> +obj-$(CONFIG_XTENSA) += stubs.o
>> 
>> Not sure it is acceptable to do it that way.
>> 
>> There should likely be something like a CONFIG_ARCH_WANTS_KCSAN_STUBS in 
>> KCSAN's Kconfig then PPC32 and XTENSA should select it.
> 
> The longer I think about it, since these stubs all BUG() anyway, perhaps
> we ought to just avoid them altogether. If you delete all the stubs from
> ppc and xtensa, but do this:
> 
> | diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c
> | index 54d077e1a2dc..8169d6dadd0e 100644
> | --- a/kernel/kcsan/core.c
> | +++ b/kernel/kcsan/core.c
> | @@ -1261,7 +1261,9 @@ static __always_inline void kcsan_atomic_builtin_memorder(int memorder)
> |  DEFINE_TSAN_ATOMIC_OPS(8);
> |  DEFINE_TSAN_ATOMIC_OPS(16);
> |  DEFINE_TSAN_ATOMIC_OPS(32);
> | +#ifdef CONFIG_64BIT
> |  DEFINE_TSAN_ATOMIC_OPS(64);
> | +#endif
> |  
> |  void __tsan_atomic_thread_fence(int memorder);
> |  void __tsan_atomic_thread_fence(int memorder)
> 
> Does that work?

This makes much more sense. Rather than assume that kcsan is the only
consumer of __atomic_*_8, and stubbing accordingly, we should just
remove its mention from relevant sub-archs.