[PATCH] kbuild: add most of Clang-specific flags unconditionally

[PATCH] kbuild: add most of Clang-specific flags unconditionally

[Masahiro Yamada]

We do not support old Clang versions. Upgrade your clang version
if any of these flags is unsupported.

Let's add flags within ifdef CONFIG_CC_IS_CLANG unconditionally,
except -fcatch-undefined-behavior.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
---

 Makefile                   | 10 +++++-----
 scripts/Makefile.extrawarn | 12 ++++++------
 2 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/Makefile b/Makefile
index bd7ae11947cb..c71ffb6f55b5 100644
--- a/Makefile
+++ b/Makefile
@@ -731,15 +731,15 @@ stackp-flags-$(CONFIG_STACKPROTECTOR_STRONG)      := -fstack-protector-strong
 KBUILD_CFLAGS += $(stackp-flags-y)
 
 ifdef CONFIG_CC_IS_CLANG
-KBUILD_CPPFLAGS += $(call cc-option,-Qunused-arguments,)
-KBUILD_CFLAGS += $(call cc-disable-warning, format-invalid-specifier)
-KBUILD_CFLAGS += $(call cc-disable-warning, gnu)
+KBUILD_CPPFLAGS += -Qunused-arguments
+KBUILD_CFLAGS += -Wno-format-invalid-specifier
+KBUILD_CFLAGS += -Wno-gnu
 # Quiet clang warning: comparison of unsigned expression < 0 is always false
-KBUILD_CFLAGS += $(call cc-disable-warning, tautological-compare)
+KBUILD_CFLAGS += -Wno-tautological-compare
 # CLANG uses a _MergedGlobals as optimization, but this breaks modpost, as the
 # source of a reference will be _MergedGlobals and not on of the whitelisted names.
 # See modpost pattern 2
-KBUILD_CFLAGS += $(call cc-option, -mno-global-merge,)
+KBUILD_CFLAGS += -mno-global-merge
 KBUILD_CFLAGS += $(call cc-option, -fcatch-undefined-behavior)
 else
 
diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
index 768306add591..523c4cafe2dc 100644
--- a/scripts/Makefile.extrawarn
+++ b/scripts/Makefile.extrawarn
@@ -66,11 +66,11 @@ KBUILD_CFLAGS += $(warning)
 else
 
 ifdef CONFIG_CC_IS_CLANG
-KBUILD_CFLAGS += $(call cc-disable-warning, initializer-overrides)
-KBUILD_CFLAGS += $(call cc-disable-warning, unused-value)
-KBUILD_CFLAGS += $(call cc-disable-warning, format)
-KBUILD_CFLAGS += $(call cc-disable-warning, sign-compare)
-KBUILD_CFLAGS += $(call cc-disable-warning, format-zero-length)
-KBUILD_CFLAGS += $(call cc-disable-warning, uninitialized)
+KBUILD_CFLAGS += -Wno-initializer-overrides
+KBUILD_CFLAGS += -Wno-unused-value
+KBUILD_CFLAGS += -Wno-format
+KBUILD_CFLAGS += -Wno-sign-compare
+KBUILD_CFLAGS += -Wno-format-zero-length
+KBUILD_CFLAGS += -Wno-uninitialized
 endif
 endif
-- 
2.17.1

Re: [PATCH] kbuild: add most of Clang-specific flags unconditionally

[Sedat Dilek]

On Thu, May 9, 2019 at 8:45 AM Masahiro Yamada
<yamada.masahiro@socionext.com> wrote:
>
> We do not support old Clang versions. Upgrade your clang version
> if any of these flags is unsupported.
>
> Let's add flags within ifdef CONFIG_CC_IS_CLANG unconditionally,
> except -fcatch-undefined-behavior.
>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

Looks good to me.

Reviewed-by: Sedat Dilek <sedat.dilek@gmail.com>

Just as sidenote:
I experimented with a snapshot version of clang-9 and lld-9 and could
build, link and boot on bare-metal with '-mglobal-merge' on
Debian/buster AMD64.
But forgot to document in [1].

[1] https://github.com/ClangBuiltLinux/linux/issues/431

> ---
>
>  Makefile                   | 10 +++++-----
>  scripts/Makefile.extrawarn | 12 ++++++------
>  2 files changed, 11 insertions(+), 11 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index bd7ae11947cb..c71ffb6f55b5 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -731,15 +731,15 @@ stackp-flags-$(CONFIG_STACKPROTECTOR_STRONG)      := -fstack-protector-strong
>  KBUILD_CFLAGS += $(stackp-flags-y)
>
>  ifdef CONFIG_CC_IS_CLANG
> -KBUILD_CPPFLAGS += $(call cc-option,-Qunused-arguments,)
> -KBUILD_CFLAGS += $(call cc-disable-warning, format-invalid-specifier)
> -KBUILD_CFLAGS += $(call cc-disable-warning, gnu)
> +KBUILD_CPPFLAGS += -Qunused-arguments
> +KBUILD_CFLAGS += -Wno-format-invalid-specifier
> +KBUILD_CFLAGS += -Wno-gnu
>  # Quiet clang warning: comparison of unsigned expression < 0 is always false
> -KBUILD_CFLAGS += $(call cc-disable-warning, tautological-compare)
> +KBUILD_CFLAGS += -Wno-tautological-compare
>  # CLANG uses a _MergedGlobals as optimization, but this breaks modpost, as the
>  # source of a reference will be _MergedGlobals and not on of the whitelisted names.
>  # See modpost pattern 2
> -KBUILD_CFLAGS += $(call cc-option, -mno-global-merge,)
> +KBUILD_CFLAGS += -mno-global-merge
>  KBUILD_CFLAGS += $(call cc-option, -fcatch-undefined-behavior)
>  else
>
> diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
> index 768306add591..523c4cafe2dc 100644
> --- a/scripts/Makefile.extrawarn
> +++ b/scripts/Makefile.extrawarn
> @@ -66,11 +66,11 @@ KBUILD_CFLAGS += $(warning)
>  else
>
>  ifdef CONFIG_CC_IS_CLANG
> -KBUILD_CFLAGS += $(call cc-disable-warning, initializer-overrides)
> -KBUILD_CFLAGS += $(call cc-disable-warning, unused-value)
> -KBUILD_CFLAGS += $(call cc-disable-warning, format)
> -KBUILD_CFLAGS += $(call cc-disable-warning, sign-compare)
> -KBUILD_CFLAGS += $(call cc-disable-warning, format-zero-length)
> -KBUILD_CFLAGS += $(call cc-disable-warning, uninitialized)
> +KBUILD_CFLAGS += -Wno-initializer-overrides
> +KBUILD_CFLAGS += -Wno-unused-value
> +KBUILD_CFLAGS += -Wno-format
> +KBUILD_CFLAGS += -Wno-sign-compare
> +KBUILD_CFLAGS += -Wno-format-zero-length
> +KBUILD_CFLAGS += -Wno-uninitialized
>  endif
>  endif
> --
> 2.17.1
>
> --
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Re: [PATCH] kbuild: add most of Clang-specific flags unconditionally

[Nathan Chancellor]

On Thu, May 09, 2019 at 03:44:55PM +0900, Masahiro Yamada wrote:
> We do not support old Clang versions. Upgrade your clang version
> if any of these flags is unsupported.
> 
> Let's add flags within ifdef CONFIG_CC_IS_CLANG unconditionally,
> except -fcatch-undefined-behavior.
> 
> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
> ---
> 
>  Makefile                   | 10 +++++-----
>  scripts/Makefile.extrawarn | 12 ++++++------
>  2 files changed, 11 insertions(+), 11 deletions(-)
> 
> diff --git a/Makefile b/Makefile
> index bd7ae11947cb..c71ffb6f55b5 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -731,15 +731,15 @@ stackp-flags-$(CONFIG_STACKPROTECTOR_STRONG)      := -fstack-protector-strong
>  KBUILD_CFLAGS += $(stackp-flags-y)
>  
>  ifdef CONFIG_CC_IS_CLANG
> -KBUILD_CPPFLAGS += $(call cc-option,-Qunused-arguments,)
> -KBUILD_CFLAGS += $(call cc-disable-warning, format-invalid-specifier)
> -KBUILD_CFLAGS += $(call cc-disable-warning, gnu)
> +KBUILD_CPPFLAGS += -Qunused-arguments
> +KBUILD_CFLAGS += -Wno-format-invalid-specifier
> +KBUILD_CFLAGS += -Wno-gnu
>  # Quiet clang warning: comparison of unsigned expression < 0 is always false
> -KBUILD_CFLAGS += $(call cc-disable-warning, tautological-compare)
> +KBUILD_CFLAGS += -Wno-tautological-compare
>  # CLANG uses a _MergedGlobals as optimization, but this breaks modpost, as the
>  # source of a reference will be _MergedGlobals and not on of the whitelisted names.
>  # See modpost pattern 2
> -KBUILD_CFLAGS += $(call cc-option, -mno-global-merge,)
> +KBUILD_CFLAGS += -mno-global-merge
>  KBUILD_CFLAGS += $(call cc-option, -fcatch-undefined-behavior)

I think we should just remove this, I'm fairly confident the kernel
can't be reliably compiled with anything earlier than Clang 4 (Pixel 2
was shipped with it but had some hacks, this commit is from Clang 3.5):

https://github.com/llvm/llvm-project/commit/cb3f812b6b9fab8f3b41414f24e90222170417b4

Otherwise:

Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>

>  else
>  
> diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
> index 768306add591..523c4cafe2dc 100644
> --- a/scripts/Makefile.extrawarn
> +++ b/scripts/Makefile.extrawarn
> @@ -66,11 +66,11 @@ KBUILD_CFLAGS += $(warning)
>  else
>  
>  ifdef CONFIG_CC_IS_CLANG
> -KBUILD_CFLAGS += $(call cc-disable-warning, initializer-overrides)
> -KBUILD_CFLAGS += $(call cc-disable-warning, unused-value)
> -KBUILD_CFLAGS += $(call cc-disable-warning, format)
> -KBUILD_CFLAGS += $(call cc-disable-warning, sign-compare)
> -KBUILD_CFLAGS += $(call cc-disable-warning, format-zero-length)
> -KBUILD_CFLAGS += $(call cc-disable-warning, uninitialized)
> +KBUILD_CFLAGS += -Wno-initializer-overrides
> +KBUILD_CFLAGS += -Wno-unused-value
> +KBUILD_CFLAGS += -Wno-format
> +KBUILD_CFLAGS += -Wno-sign-compare
> +KBUILD_CFLAGS += -Wno-format-zero-length
> +KBUILD_CFLAGS += -Wno-uninitialized
>  endif
>  endif
> -- 
> 2.17.1
> 

Re: [PATCH] kbuild: add most of Clang-specific flags unconditionally

[Masahiro Yamada]

Hi.

On Thu, May 9, 2019 at 8:15 PM Nathan Chancellor
<natechancellor@gmail.com> wrote:
>
> On Thu, May 09, 2019 at 03:44:55PM +0900, Masahiro Yamada wrote:
> > We do not support old Clang versions. Upgrade your clang version
> > if any of these flags is unsupported.
> >
> > Let's add flags within ifdef CONFIG_CC_IS_CLANG unconditionally,
> > except -fcatch-undefined-behavior.
> >
> > Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
> > ---
> >
> >  Makefile                   | 10 +++++-----
> >  scripts/Makefile.extrawarn | 12 ++++++------
> >  2 files changed, 11 insertions(+), 11 deletions(-)
> >
> > diff --git a/Makefile b/Makefile
> > index bd7ae11947cb..c71ffb6f55b5 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -731,15 +731,15 @@ stackp-flags-$(CONFIG_STACKPROTECTOR_STRONG)      := -fstack-protector-strong
> >  KBUILD_CFLAGS += $(stackp-flags-y)
> >
> >  ifdef CONFIG_CC_IS_CLANG
> > -KBUILD_CPPFLAGS += $(call cc-option,-Qunused-arguments,)
> > -KBUILD_CFLAGS += $(call cc-disable-warning, format-invalid-specifier)
> > -KBUILD_CFLAGS += $(call cc-disable-warning, gnu)
> > +KBUILD_CPPFLAGS += -Qunused-arguments
> > +KBUILD_CFLAGS += -Wno-format-invalid-specifier
> > +KBUILD_CFLAGS += -Wno-gnu
> >  # Quiet clang warning: comparison of unsigned expression < 0 is always false
> > -KBUILD_CFLAGS += $(call cc-disable-warning, tautological-compare)
> > +KBUILD_CFLAGS += -Wno-tautological-compare
> >  # CLANG uses a _MergedGlobals as optimization, but this breaks modpost, as the
> >  # source of a reference will be _MergedGlobals and not on of the whitelisted names.
> >  # See modpost pattern 2
> > -KBUILD_CFLAGS += $(call cc-option, -mno-global-merge,)
> > +KBUILD_CFLAGS += -mno-global-merge
> >  KBUILD_CFLAGS += $(call cc-option, -fcatch-undefined-behavior)
>
> I think we should just remove this, I'm fairly confident the kernel
> can't be reliably compiled with anything earlier than Clang 4 (Pixel 2
> was shipped with it but had some hacks, this commit is from Clang 3.5):
>
> https://github.com/llvm/llvm-project/commit/cb3f812b6b9fab8f3b41414f24e90222170417b4


Oh, I did not know this was deprecated.

Could you send a patch to remove it
with filling the commit log ?


Thanks.



-- 
Best Regards
Masahiro Yamada

Re: [PATCH] kbuild: add most of Clang-specific flags unconditionally

[Nathan Chancellor]

On Thu, May 09, 2019 at 08:35:05PM +0900, Masahiro Yamada wrote:
> Hi.
> 
> On Thu, May 9, 2019 at 8:15 PM Nathan Chancellor
> <natechancellor@gmail.com> wrote:
> >
> > On Thu, May 09, 2019 at 03:44:55PM +0900, Masahiro Yamada wrote:
> > > We do not support old Clang versions. Upgrade your clang version
> > > if any of these flags is unsupported.
> > >
> > > Let's add flags within ifdef CONFIG_CC_IS_CLANG unconditionally,
> > > except -fcatch-undefined-behavior.
> > >
> > > Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
> > > ---
> > >
> > >  Makefile                   | 10 +++++-----
> > >  scripts/Makefile.extrawarn | 12 ++++++------
> > >  2 files changed, 11 insertions(+), 11 deletions(-)
> > >
> > > diff --git a/Makefile b/Makefile
> > > index bd7ae11947cb..c71ffb6f55b5 100644
> > > --- a/Makefile
> > > +++ b/Makefile
> > > @@ -731,15 +731,15 @@ stackp-flags-$(CONFIG_STACKPROTECTOR_STRONG)      := -fstack-protector-strong
> > >  KBUILD_CFLAGS += $(stackp-flags-y)
> > >
> > >  ifdef CONFIG_CC_IS_CLANG
> > > -KBUILD_CPPFLAGS += $(call cc-option,-Qunused-arguments,)
> > > -KBUILD_CFLAGS += $(call cc-disable-warning, format-invalid-specifier)
> > > -KBUILD_CFLAGS += $(call cc-disable-warning, gnu)
> > > +KBUILD_CPPFLAGS += -Qunused-arguments
> > > +KBUILD_CFLAGS += -Wno-format-invalid-specifier
> > > +KBUILD_CFLAGS += -Wno-gnu
> > >  # Quiet clang warning: comparison of unsigned expression < 0 is always false
> > > -KBUILD_CFLAGS += $(call cc-disable-warning, tautological-compare)
> > > +KBUILD_CFLAGS += -Wno-tautological-compare
> > >  # CLANG uses a _MergedGlobals as optimization, but this breaks modpost, as the
> > >  # source of a reference will be _MergedGlobals and not on of the whitelisted names.
> > >  # See modpost pattern 2
> > > -KBUILD_CFLAGS += $(call cc-option, -mno-global-merge,)
> > > +KBUILD_CFLAGS += -mno-global-merge
> > >  KBUILD_CFLAGS += $(call cc-option, -fcatch-undefined-behavior)
> >
> > I think we should just remove this, I'm fairly confident the kernel
> > can't be reliably compiled with anything earlier than Clang 4 (Pixel 2
> > was shipped with it but had some hacks, this commit is from Clang 3.5):
> >
> > https://github.com/llvm/llvm-project/commit/cb3f812b6b9fab8f3b41414f24e90222170417b4
> 
> 
> Oh, I did not know this was deprecated.
> 
> Could you send a patch to remove it
> with filling the commit log ?

Sure!

> 
> 
> Thanks.
> 
> 
> 
> -- 
> Best Regards
> Masahiro Yamada
> 
> -- 
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> For more options, visit https://groups.google.com/d/optout.

[PATCH] Makefile: Don't try to add '-fcatch-undefined-behavior' flag

[Nathan Chancellor]

This is no longer a valid option in clang, it was removed in 3.5, which
we don't support.

https://github.com/llvm/llvm-project/commit/cb3f812b6b9fab8f3b41414f24e90222170417b4

Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
---

Let me know if you want this incremental to your patch. I figured it
made more sense to remove this then do the cc-option/cc-disable-warning
removal because it will simplify the commit message.

 Makefile | 1 -
 1 file changed, 1 deletion(-)

diff --git a/Makefile b/Makefile
index d24f5a8009ee..e4788eb2c9b9 100644
--- a/Makefile
+++ b/Makefile
@@ -740,7 +740,6 @@ KBUILD_CFLAGS += $(call cc-disable-warning, tautological-compare)
 # source of a reference will be _MergedGlobals and not on of the whitelisted names.
 # See modpost pattern 2
 KBUILD_CFLAGS += $(call cc-option, -mno-global-merge,)
-KBUILD_CFLAGS += $(call cc-option, -fcatch-undefined-behavior)
 else
 
 # These warnings generated too much noise in a regular build.
-- 
2.21.0

Re: [PATCH] Makefile: Don't try to add '-fcatch-undefined-behavior' flag

[Masahiro Yamada]

On Thu, May 9, 2019 at 8:49 PM Nathan Chancellor
<natechancellor@gmail.com> wrote:
>
> This is no longer a valid option in clang, it was removed in 3.5, which
> we don't support.
>
> https://github.com/llvm/llvm-project/commit/cb3f812b6b9fab8f3b41414f24e90222170417b4
>
> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
> ---
>
> Let me know if you want this incremental to your patch.

No problem. I will rebase mine on top of this.

> I figured it
> made more sense to remove this then do the cc-option/cc-disable-warning
> removal because it will simplify the commit message.

Yes, I agree!


Thanks.

-- 
Best Regards
Masahiro Yamada

Re: [PATCH] Makefile: Don't try to add '-fcatch-undefined-behavior' flag

[Sedat Dilek]

On Thu, May 9, 2019 at 1:49 PM Nathan Chancellor
<natechancellor@gmail.com> wrote:
>
> This is no longer a valid option in clang, it was removed in 3.5, which
> we don't support.
>
> https://github.com/llvm/llvm-project/commit/cb3f812b6b9fab8f3b41414f24e90222170417b4
>

Cool.

Can you test with -mglobal-merge (inverted -mno-global-merge) which is
default for Clang?
I could build, link and boot with my llvm-toolchain (incl. lld-9) on x86-64.

Maybe this is also no more needed?

Thanks.

- Sedat -

> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
> ---
>
> Let me know if you want this incremental to your patch. I figured it
> made more sense to remove this then do the cc-option/cc-disable-warning
> removal because it will simplify the commit message.
>
>  Makefile | 1 -
>  1 file changed, 1 deletion(-)
>
> diff --git a/Makefile b/Makefile
> index d24f5a8009ee..e4788eb2c9b9 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -740,7 +740,6 @@ KBUILD_CFLAGS += $(call cc-disable-warning, tautological-compare)
>  # source of a reference will be _MergedGlobals and not on of the whitelisted names.
>  # See modpost pattern 2
>  KBUILD_CFLAGS += $(call cc-option, -mno-global-merge,)
> -KBUILD_CFLAGS += $(call cc-option, -fcatch-undefined-behavior)
>  else
>
>  # These warnings generated too much noise in a regular build.
> --
> 2.21.0
>
> --
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Re: [PATCH] Makefile: Don't try to add '-fcatch-undefined-behavior' flag

[Nick Desaulniers]

> On Thu, May 9, 2019 at 1:49 PM Nathan Chancellor
> <natechancellor@gmail.com> wrote:
> >
> > This is no longer a valid option in clang, it was removed in 3.5, which
> > we don't support.
> >
> > https://github.com/llvm/llvm-project/commit/cb3f812b6b9fab8f3b41414f24e90222170417b4

lol, good catch.
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

> >
>
> Cool.
>
> Can you test with -mglobal-merge (inverted -mno-global-merge) which is
> default for Clang?

Looks like these were added in r234668 in 2015, which would've been
Clang 3.6.2, according to:
http://releases.llvm.org/

I'd be fine with dropping the option check there.

There's a few here (-Qunused-arguments) that don't need cc-option
checks.  I recommend someone audit all of them, rather than send a
bunch of little patches.
-- 
Thanks,
~Nick Desaulniers

Re: [PATCH] kbuild: add most of Clang-specific flags unconditionally

[Nick Desaulniers]

> On Thu, May 09, 2019 at 03:44:55PM +0900, Masahiro Yamada wrote:
> > We do not support old Clang versions. Upgrade your clang version
> > if any of these flags is unsupported.
> >
> > Let's add flags within ifdef CONFIG_CC_IS_CLANG unconditionally,
> > except -fcatch-undefined-behavior.
> >
> > Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
> > ---
> >
> >  Makefile                   | 10 +++++-----
> >  scripts/Makefile.extrawarn | 12 ++++++------
> >  2 files changed, 11 insertions(+), 11 deletions(-)
> >
> > diff --git a/Makefile b/Makefile
> > index bd7ae11947cb..c71ffb6f55b5 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -731,15 +731,15 @@ stackp-flags-$(CONFIG_STACKPROTECTOR_STRONG)      := -fstack-protector-strong
> >  KBUILD_CFLAGS += $(stackp-flags-y)
> >
> >  ifdef CONFIG_CC_IS_CLANG
> > -KBUILD_CPPFLAGS += $(call cc-option,-Qunused-arguments,)
> > -KBUILD_CFLAGS += $(call cc-disable-warning, format-invalid-specifier)
> > -KBUILD_CFLAGS += $(call cc-disable-warning, gnu)
> > +KBUILD_CPPFLAGS += -Qunused-arguments
> > +KBUILD_CFLAGS += -Wno-format-invalid-specifier
> > +KBUILD_CFLAGS += -Wno-gnu
> >  # Quiet clang warning: comparison of unsigned expression < 0 is always false
> > -KBUILD_CFLAGS += $(call cc-disable-warning, tautological-compare)
> > +KBUILD_CFLAGS += -Wno-tautological-compare
> >  # CLANG uses a _MergedGlobals as optimization, but this breaks modpost, as the
> >  # source of a reference will be _MergedGlobals and not on of the whitelisted names.
> >  # See modpost pattern 2
> > -KBUILD_CFLAGS += $(call cc-option, -mno-global-merge,)
> > +KBUILD_CFLAGS += -mno-global-merge
> >  KBUILD_CFLAGS += $(call cc-option, -fcatch-undefined-behavior)
>
> I think we should just remove this, I'm fairly confident the kernel
> can't be reliably compiled with anything earlier than Clang 4 (Pixel 2
> was shipped with it but had some hacks, this commit is from Clang 3.5):

Yeah, clang-4 is usually what I test these with, as that's the
earliest known version of Clang that I ever had success with.
Hopefully a lot of things will stabilize for the clang-9 release.

Anyways, I checked these all w/ godbolt w/ clang-4.
Tested-by: Nick Desaulniers <ndesaulniers@google.com>

>
> https://github.com/llvm/llvm-project/commit/cb3f812b6b9fab8f3b41414f24e90222170417b4
>
> Otherwise:
>
> Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
>
> >  else
> >
> > diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
> > index 768306add591..523c4cafe2dc 100644
> > --- a/scripts/Makefile.extrawarn
> > +++ b/scripts/Makefile.extrawarn
> > @@ -66,11 +66,11 @@ KBUILD_CFLAGS += $(warning)
> >  else
> >
> >  ifdef CONFIG_CC_IS_CLANG
> > -KBUILD_CFLAGS += $(call cc-disable-warning, initializer-overrides)
> > -KBUILD_CFLAGS += $(call cc-disable-warning, unused-value)
> > -KBUILD_CFLAGS += $(call cc-disable-warning, format)
> > -KBUILD_CFLAGS += $(call cc-disable-warning, sign-compare)
> > -KBUILD_CFLAGS += $(call cc-disable-warning, format-zero-length)
> > -KBUILD_CFLAGS += $(call cc-disable-warning, uninitialized)
> > +KBUILD_CFLAGS += -Wno-initializer-overrides
> > +KBUILD_CFLAGS += -Wno-unused-value
> > +KBUILD_CFLAGS += -Wno-format
> > +KBUILD_CFLAGS += -Wno-sign-compare
> > +KBUILD_CFLAGS += -Wno-format-zero-length
> > +KBUILD_CFLAGS += -Wno-uninitialized
> >  endif
> >  endif
> > --
> > 2.17.1
> >



-- 
Thanks,
~Nick Desaulniers

Re: [PATCH] kbuild: add most of Clang-specific flags unconditionally

[Masahiro Yamada]

On Thu, May 9, 2019 at 4:06 PM Sedat Dilek <sedat.dilek@gmail.com> wrote:
>
> On Thu, May 9, 2019 at 8:45 AM Masahiro Yamada
> <yamada.masahiro@socionext.com> wrote:
> >
> > We do not support old Clang versions. Upgrade your clang version
> > if any of these flags is unsupported.
> >
> > Let's add flags within ifdef CONFIG_CC_IS_CLANG unconditionally,
> > except -fcatch-undefined-behavior.
> >
> > Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
>
> Looks good to me.
>
> Reviewed-by: Sedat Dilek <sedat.dilek@gmail.com>
>
> Just as sidenote:
> I experimented with a snapshot version of clang-9 and lld-9 and could
> build, link and boot on bare-metal with '-mglobal-merge' on
> Debian/buster AMD64.


The comment says
 # CLANG uses a _MergedGlobals as optimization, but this breaks modpost, as the
 # source of a reference will be _MergedGlobals and not on of the
whitelisted names.
 # See modpost pattern 2

So, it seems it is just a matter of modpost,
but I am not sure enough.

This flag has been here since the initial support.
(61163efae02040f66a95c8ed17f4407951ba58fa)


Perhaps, we should review clang flags one by one again?




> But forgot to document in [1].
>
> [1] https://github.com/ClangBuiltLinux/linux/issues/431



-- 
Best Regards
Masahiro Yamada

Re: [PATCH] kbuild: add most of Clang-specific flags unconditionally

[Nick Desaulniers]

On Fri, May 10, 2019 at 6:54 AM Masahiro Yamada
<yamada.masahiro@socionext.com> wrote:
>
> On Thu, May 9, 2019 at 4:06 PM Sedat Dilek <sedat.dilek@gmail.com> wrote:
> >
> > On Thu, May 9, 2019 at 8:45 AM Masahiro Yamada
> > <yamada.masahiro@socionext.com> wrote:
> > >
> > > We do not support old Clang versions. Upgrade your clang version
> > > if any of these flags is unsupported.
> > >
> > > Let's add flags within ifdef CONFIG_CC_IS_CLANG unconditionally,
> > > except -fcatch-undefined-behavior.
> > >
> > > Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
> >
> > Looks good to me.
> >
> > Reviewed-by: Sedat Dilek <sedat.dilek@gmail.com>
> >
> > Just as sidenote:
> > I experimented with a snapshot version of clang-9 and lld-9 and could
> > build, link and boot on bare-metal with '-mglobal-merge' on
> > Debian/buster AMD64.
>
>
> The comment says
>  # CLANG uses a _MergedGlobals as optimization, but this breaks modpost, as the
>  # source of a reference will be _MergedGlobals and not on of the
> whitelisted names.
>  # See modpost pattern 2
>
> So, it seems it is just a matter of modpost,
> but I am not sure enough.
>
> This flag has been here since the initial support.
> (61163efae02040f66a95c8ed17f4407951ba58fa)
>
>
> Perhaps, we should review clang flags one by one again?

Yes, it's always good to re-evaluate if something is just cruft and
can be removed.

+Behan

I don't quite understand the comment about _MergedGlobals, Behan, do
happen to have more context?
-- 
Thanks,
~Nick Desaulniers

Re: [PATCH] Makefile: Don't try to add '-fcatch-undefined-behavior' flag

[Masahiro Yamada]

On Thu, May 9, 2019 at 8:49 PM Nathan Chancellor
<natechancellor@gmail.com> wrote:
>
> This is no longer a valid option in clang, it was removed in 3.5, which
> we don't support.
>
> https://github.com/llvm/llvm-project/commit/cb3f812b6b9fab8f3b41414f24e90222170417b4
>
> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
> ---
>
> Let me know if you want this incremental to your patch. I figured it
> made more sense to remove this then do the cc-option/cc-disable-warning
> removal because it will simplify the commit message.

Applied to linux-kbuild.
Thanks.


>  Makefile | 1 -
>  1 file changed, 1 deletion(-)
>
> diff --git a/Makefile b/Makefile
> index d24f5a8009ee..e4788eb2c9b9 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -740,7 +740,6 @@ KBUILD_CFLAGS += $(call cc-disable-warning, tautological-compare)
>  # source of a reference will be _MergedGlobals and not on of the whitelisted names.
>  # See modpost pattern 2
>  KBUILD_CFLAGS += $(call cc-option, -mno-global-merge,)
> -KBUILD_CFLAGS += $(call cc-option, -fcatch-undefined-behavior)
>  else
>
>  # These warnings generated too much noise in a regular build.
> --
> 2.21.0
>


-- 
Best Regards
Masahiro Yamada