[PATCH v2] x86/build: fix compiler support check for CONFIG_RETPOLINE

[PATCH v2] x86/build: fix compiler support check for CONFIG_RETPOLINE

[Masahiro Yamada]

It is troublesome to add a diagnostic like this to the Makefile
parse stage because the top-level Makefile could be parsed with
a stale include/config/auto.conf.

Once you are hit by the error about non-retpoline compiler, the
compilation still breaks even after disabling CONFIG_RETPOLINE.

The easiest fix is to move this check to the "archprepare" like commit
829fe4aa9ac1 ("x86: Allow generating user-space headers without a
compiler") did.

Link: https://lkml.org/lkml/2018/12/4/206
Fixes: 4cd24de3a098 ("x86/retpoline: Make CONFIG_RETPOLINE depend on compiler support")
Reported-by: Meelis Roos <mroos@linux.ee>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
---

Changes in v2:
  - Revive ifdef CONFIG_RETPOLINE surrounding the KBUILD_CFLAGS addition
  - Rephase the commit log a bit, hoping the cause of the issue will be clearer

 arch/x86/Makefile | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index f5d7f41..75ef499 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -220,9 +220,6 @@ KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
 
 # Avoid indirect branches in kernel to deal with Spectre
 ifdef CONFIG_RETPOLINE
-ifeq ($(RETPOLINE_CFLAGS),)
-  $(error You are building kernel with non-retpoline compiler, please update your compiler.)
-endif
   KBUILD_CFLAGS += $(RETPOLINE_CFLAGS)
 endif
 
@@ -307,6 +304,13 @@ ifndef CC_HAVE_ASM_GOTO
 	@echo Compiler lacks asm-goto support.
 	@exit 1
 endif
+ifdef CONFIG_RETPOLINE
+ifeq ($(RETPOLINE_CFLAGS),)
+	@echo "You are building kernel with non-retpoline compiler." >&2
+	@echo "Please update your compiler." >&2
+	@false
+endif
+endif
 
 archclean:
 	$(Q)rm -rf $(objtree)/arch/i386
-- 
2.7.4

Re: [PATCH v2] x86/build: fix compiler support check for CONFIG_RETPOLINE

[Meelis Roos]

05.12.18 08:27 Masahiro Yamada kirjutas:
> The easiest fix is to move this check to the "archprepare" like commit
> 829fe4aa9ac1 ("x86: Allow generating user-space headers without a
> compiler") did.
> 
> Link: https://lkml.org/lkml/2018/12/4/206
> Fixes: 4cd24de3a098 ("x86/retpoline: Make CONFIG_RETPOLINE depend on compiler support")
> Reported-by: Meelis Roos <mroos@linux.ee>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
> ---
> 
> Changes in v2:
>    - Revive ifdef CONFIG_RETPOLINE surrounding the KBUILD_CFLAGS addition
>    - Rephase the commit log a bit, hoping the cause of the issue will be clearer

Works for me - first it did

scripts/kconfig/conf  --syncconfig Kconfig

and then started compiling. The #define is gone from include/linux.

Thank you!

-- 
Meelis Roos <mroos@linux.ee>

Re: [PATCH v2] x86/build: fix compiler support check for CONFIG_RETPOLINE

[Zhenzhong Duan]

On 2018/12/5 14:27, Masahiro Yamada wrote:
> It is troublesome to add a diagnostic like this to the Makefile
> parse stage because the top-level Makefile could be parsed with
> a stale include/config/auto.conf.
>
> Once you are hit by the error about non-retpoline compiler, the
> compilation still breaks even after disabling CONFIG_RETPOLINE.
>
> The easiest fix is to move this check to the "archprepare" like commit
> 829fe4aa9ac1 ("x86: Allow generating user-space headers without a
> compiler") did.
>
> Link: https://lkml.org/lkml/2018/12/4/206
> Fixes: 4cd24de3a098 ("x86/retpoline: Make CONFIG_RETPOLINE depend on compiler support")
> Reported-by: Meelis Roos <mroos@linux.ee>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
> ---
>
> Changes in v2:
>    - Revive ifdef CONFIG_RETPOLINE surrounding the KBUILD_CFLAGS addition
>    - Rephase the commit log a bit, hoping the cause of the issue will be clearer
>
>   arch/x86/Makefile | 10 +++++++---
>   1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> index f5d7f41..75ef499 100644
> --- a/arch/x86/Makefile
> +++ b/arch/x86/Makefile
> @@ -220,9 +220,6 @@ KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
>   
>   # Avoid indirect branches in kernel to deal with Spectre
>   ifdef CONFIG_RETPOLINE
> -ifeq ($(RETPOLINE_CFLAGS),)
> -  $(error You are building kernel with non-retpoline compiler, please update your compiler.)
> -endif
>     KBUILD_CFLAGS += $(RETPOLINE_CFLAGS)
>   endif
>   
> @@ -307,6 +304,13 @@ ifndef CC_HAVE_ASM_GOTO
>   	@echo Compiler lacks asm-goto support.
>   	@exit 1
>   endif
> +ifdef CONFIG_RETPOLINE
> +ifeq ($(RETPOLINE_CFLAGS),)
> +	@echo "You are building kernel with non-retpoline compiler." >&2
> +	@echo "Please update your compiler." >&2
> +	@false
> +endif
> +endif
>   
>   archclean:
>   	$(Q)rm -rf $(objtree)/arch/i386
Acked-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>

-- 
Regards
Zhenzhong

Re: [PATCH v2] x86/build: fix compiler support check for CONFIG_RETPOLINE

[Gi-Oh Kim]

On Wed, Dec 5, 2018 at 8:11 AM Zhenzhong Duan <zhenzhong.duan@oracle.com> wrote:
>
>
> On 2018/12/5 14:27, Masahiro Yamada wrote:
> > It is troublesome to add a diagnostic like this to the Makefile
> > parse stage because the top-level Makefile could be parsed with
> > a stale include/config/auto.conf.
> >
> > Once you are hit by the error about non-retpoline compiler, the
> > compilation still breaks even after disabling CONFIG_RETPOLINE.
> >
> > The easiest fix is to move this check to the "archprepare" like commit
> > 829fe4aa9ac1 ("x86: Allow generating user-space headers without a
> > compiler") did.
> >
> > Link: https://lkml.org/lkml/2018/12/4/206
> > Fixes: 4cd24de3a098 ("x86/retpoline: Make CONFIG_RETPOLINE depend on compiler support")
> > Reported-by: Meelis Roos <mroos@linux.ee>
> > Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
> > ---
> >
> > Changes in v2:
> >    - Revive ifdef CONFIG_RETPOLINE surrounding the KBUILD_CFLAGS addition
> >    - Rephase the commit log a bit, hoping the cause of the issue will be clearer
> >
> >   arch/x86/Makefile | 10 +++++++---
> >   1 file changed, 7 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> > index f5d7f41..75ef499 100644
> > --- a/arch/x86/Makefile
> > +++ b/arch/x86/Makefile
> > @@ -220,9 +220,6 @@ KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
> >
> >   # Avoid indirect branches in kernel to deal with Spectre
> >   ifdef CONFIG_RETPOLINE
> > -ifeq ($(RETPOLINE_CFLAGS),)
> > -  $(error You are building kernel with non-retpoline compiler, please update your compiler.)
> > -endif
> >     KBUILD_CFLAGS += $(RETPOLINE_CFLAGS)
> >   endif
> >
> > @@ -307,6 +304,13 @@ ifndef CC_HAVE_ASM_GOTO
> >       @echo Compiler lacks asm-goto support.
> >       @exit 1
> >   endif
> > +ifdef CONFIG_RETPOLINE
> > +ifeq ($(RETPOLINE_CFLAGS),)
> > +     @echo "You are building kernel with non-retpoline compiler." >&2
> > +     @echo "Please update your compiler." >&2
> > +     @false
> > +endif
> > +endif
> >
> >   archclean:
> >       $(Q)rm -rf $(objtree)/arch/i386
> Acked-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
>
> --
> Regards
> Zhenzhong
>

Hi,

I think this patch needs to be merged to linux-stable 4.14.y branch.
Following is what I did to reproduce the problem.
The problem is gone after applying the patch.

1. I created and installed a headers package as following.
make -j7 deb-pkg
cd ..
sudo dpkg -i linux-headers-4.14.89+_4.14.89+-18_amd64.deb

2. I managed to re-produce the same problem as following.
gohkim@ws00837:~/study/drv$ make -C /usr/src/linux-headers-4.14.89+/
kernelrelease
make: Entering directory '/usr/src/linux-headers-4.14.89+'
arch/x86/Makefile:245: *** You are building kernel with non-retpoline
compiler, please update your compiler.. Stop.
make: Leaving directory '/usr/src/linux-headers-4.14.89+'

3. Weird thing is that it works fine if I use sudo command.
gohkim@ws00837:~/study/drv$ sudo make -C
/usr/src/linux-headers-4.14.89+/ kernelrelease
make: Entering directory '/usr/src/linux-headers-4.14.89+'
  HOSTCC  scripts/kconfig/conf.o
  HOSTCC  scripts/kconfig/zconf.tab.o
  HOSTLD  scripts/kconfig/conf
scripts/kconfig/conf  --silentoldconfig Kconfig
4.14.89
make: Leaving directory '/usr/src/linux-headers-4.14.89+'


-- 
GIOH KIM
Linux Kernel Entwickler

1&1 IONOS Cloud GmbH
Greifswalder Str. 207
D - 10405 Berlin

Tel:       +49 176 2697 8962
Fax:      +49 30 577 008 299
Email:    gi-oh.kim@cloud.ionos.com
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Geschäftsführer: Achim Weiss, Matthias Steinberg, Christoph Steffens

[tip:x86/urgent] x86/build: Fix compiler support check for CONFIG_RETPOLINE

[tip-bot for Masahiro Yamada]

Commit-ID:  10b87bc9f630a38a7f0c1e7cf13ff23fea1692ec
Gitweb:     https://git.kernel.org/tip/10b87bc9f630a38a7f0c1e7cf13ff23fea1692ec
Author:     Masahiro Yamada <yamada.masahiro@socionext.com>
AuthorDate: Wed, 5 Dec 2018 15:27:19 +0900
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Wed, 5 Dec 2018 08:42:09 +0100

x86/build: Fix compiler support check for CONFIG_RETPOLINE

It is troublesome to add a diagnostic like this to the Makefile
parse stage because the top-level Makefile could be parsed with
a stale include/config/auto.conf.

Once you are hit by the error about non-retpoline compiler, the
compilation still breaks even after disabling CONFIG_RETPOLINE.

The easiest fix is to move this check to the "archprepare" like
this commit did:

  829fe4aa9ac1 ("x86: Allow generating user-space headers without a compiler")

Reported-by: Meelis Roos <mroos@linux.ee>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Zhenzhong Duan <zhenzhong.duan@oracle.com>
Fixes: 4cd24de3a098 ("x86/retpoline: Make CONFIG_RETPOLINE depend on compiler support")
Link: http://lkml.kernel.org/r/1543991239-18476-1-git-send-email-yamada.masahiro@socionext.com
Link: https://lkml.org/lkml/2018/12/4/206
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/Makefile | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index f5d7f4134524..75ef499a66e2 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -220,9 +220,6 @@ KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
 
 # Avoid indirect branches in kernel to deal with Spectre
 ifdef CONFIG_RETPOLINE
-ifeq ($(RETPOLINE_CFLAGS),)
-  $(error You are building kernel with non-retpoline compiler, please update your compiler.)
-endif
   KBUILD_CFLAGS += $(RETPOLINE_CFLAGS)
 endif
 
@@ -307,6 +304,13 @@ ifndef CC_HAVE_ASM_GOTO
 	@echo Compiler lacks asm-goto support.
 	@exit 1
 endif
+ifdef CONFIG_RETPOLINE
+ifeq ($(RETPOLINE_CFLAGS),)
+	@echo "You are building kernel with non-retpoline compiler." >&2
+	@echo "Please update your compiler." >&2
+	@false
+endif
+endif
 
 archclean:
 	$(Q)rm -rf $(objtree)/arch/i386

[tip:x86/urgent] x86/build: Fix compiler support check for CONFIG_RETPOLINE

[tip-bot for Masahiro Yamada]

Commit-ID:  25896d073d8a0403b07e6dec56f58e6c33678207
Gitweb:     https://git.kernel.org/tip/25896d073d8a0403b07e6dec56f58e6c33678207
Author:     Masahiro Yamada <yamada.masahiro@socionext.com>
AuthorDate: Wed, 5 Dec 2018 15:27:19 +0900
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Wed, 5 Dec 2018 08:44:02 +0100

x86/build: Fix compiler support check for CONFIG_RETPOLINE

It is troublesome to add a diagnostic like this to the Makefile
parse stage because the top-level Makefile could be parsed with
a stale include/config/auto.conf.

Once you are hit by the error about non-retpoline compiler, the
compilation still breaks even after disabling CONFIG_RETPOLINE.

The easiest fix is to move this check to the "archprepare" like
this commit did:

  829fe4aa9ac1 ("x86: Allow generating user-space headers without a compiler")

Reported-by: Meelis Roos <mroos@linux.ee>
Tested-by: Meelis Roos <mroos@linux.ee>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Zhenzhong Duan <zhenzhong.duan@oracle.com>
Fixes: 4cd24de3a098 ("x86/retpoline: Make CONFIG_RETPOLINE depend on compiler support")
Link: http://lkml.kernel.org/r/1543991239-18476-1-git-send-email-yamada.masahiro@socionext.com
Link: https://lkml.org/lkml/2018/12/4/206
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/Makefile | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index f5d7f4134524..75ef499a66e2 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -220,9 +220,6 @@ KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
 
 # Avoid indirect branches in kernel to deal with Spectre
 ifdef CONFIG_RETPOLINE
-ifeq ($(RETPOLINE_CFLAGS),)
-  $(error You are building kernel with non-retpoline compiler, please update your compiler.)
-endif
   KBUILD_CFLAGS += $(RETPOLINE_CFLAGS)
 endif
 
@@ -307,6 +304,13 @@ ifndef CC_HAVE_ASM_GOTO
 	@echo Compiler lacks asm-goto support.
 	@exit 1
 endif
+ifdef CONFIG_RETPOLINE
+ifeq ($(RETPOLINE_CFLAGS),)
+	@echo "You are building kernel with non-retpoline compiler." >&2
+	@echo "Please update your compiler." >&2
+	@false
+endif
+endif
 
 archclean:
 	$(Q)rm -rf $(objtree)/arch/i386