diff mbox series

x86/build: fix compiler support check for CONFIG_RETPOLINE

Message ID 1543978802-24196-1-git-send-email-yamada.masahiro@socionext.com
State New
Headers show
Series x86/build: fix compiler support check for CONFIG_RETPOLINE | expand

Commit Message

Masahiro Yamada Dec. 5, 2018, 3 a.m. UTC 
It is wrong to add CONFIG option diagnostic to the Makefile parse
stage.

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

---

 arch/x86/Makefile | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

-- 
2.7.4

Comments

Zhenzhong Duan Dec. 5, 2018, 3:22 a.m. UTC | #1 
Hi Masahiro,


Thanks for fixing.
There is a question still confusing me. There are many CONFIG_* used in 
arch/x86/Makefile.
Will they also be impacted or not?

# grep CONFIG_ arch/x86/Makefile
ifeq ($(CONFIG_X86_32),y)
         cflags-$(CONFIG_MK8) += $(call cc-option,-march=k8)
         cflags-$(CONFIG_MPSC) += $(call cc-option,-march=nocona)
  ......
drivers-$(CONFIG_MATH_EMULATION) += arch/x86/math-emu/
drivers-$(CONFIG_PCI)      += arch/x86/pci/
drivers-$(CONFIG_OPROFILE) += arch/x86/oprofile/
drivers-$(CONFIG_PM) += arch/x86/power/
drivers-$(CONFIG_FB) += arch/x86/video/
ifeq ($(CONFIG_X86_DECODER_SELFTEST),y)

Thanks
Zhenzhong
On 2018/12/5 11:00, Masahiro Yamada wrote:
> It is wrong to add CONFIG option diagnostic to the Makefile parse

> stage.

>

> 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

> Reported-by: Meelis Roos <mroos@linux.ee>

> Fixes: 4cd24de3a098 ("x86/retpoline: Make CONFIG_RETPOLINE depend on compiler support")

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

> ---

>

>   arch/x86/Makefile | 14 ++++++++------

>   1 file changed, 8 insertions(+), 6 deletions(-)

>

> diff --git a/arch/x86/Makefile b/arch/x86/Makefile

> index f5d7f41..ae0148b 100644

> --- a/arch/x86/Makefile

> +++ b/arch/x86/Makefile

> @@ -219,12 +219,7 @@ KBUILD_CFLAGS += -Wno-sign-compare

>   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

> +KBUILD_CFLAGS += $(RETPOLINE_CFLAGS)

>   

>   archscripts: scripts_basic

>   	$(Q)$(MAKE) $(build)=arch/x86/tools relocs

> @@ -307,6 +302,13 @@ 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
Masahiro Yamada Dec. 5, 2018, 4:46 a.m. UTC | #2 
On Wed, Dec 5, 2018 at 12:23 PM Zhenzhong Duan
<zhenzhong.duan@oracle.com> wrote:
>

> Hi Masahiro,

>

>

> Thanks for fixing.

> There is a question still confusing me. There are many CONFIG_* used in

> arch/x86/Makefile.

> Will they also be impacted or not?



The top level Makefile (and arch/*/Makefile) is getting huge.
Parsing the whole Makefile everytime means,
it computes variables that may or may not be used.

$(call cc-option,...) is a bit costly,
but other parts are unnoticeable
in terms of performance.


I am addressing the use of $(error ...) / $(warning ...)
in the non-recipe context since they could break the build
for false positive reasons.




> # grep CONFIG_ arch/x86/Makefile

> ifeq ($(CONFIG_X86_32),y)

>          cflags-$(CONFIG_MK8) += $(call cc-option,-march=k8)

>          cflags-$(CONFIG_MPSC) += $(call cc-option,-march=nocona)

>   ......

> drivers-$(CONFIG_MATH_EMULATION) += arch/x86/math-emu/

> drivers-$(CONFIG_PCI)      += arch/x86/pci/

> drivers-$(CONFIG_OPROFILE) += arch/x86/oprofile/

> drivers-$(CONFIG_PM) += arch/x86/power/

> drivers-$(CONFIG_FB) += arch/x86/video/

> ifeq ($(CONFIG_X86_DECODER_SELFTEST),y)

>

> Thanks

> Zhenzhong

> On 2018/12/5 11:00, Masahiro Yamada wrote:

> > It is wrong to add CONFIG option diagnostic to the Makefile parse

> > stage.

> >

> > 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

> > Reported-by: Meelis Roos <mroos@linux.ee>

> > Fixes: 4cd24de3a098 ("x86/retpoline: Make CONFIG_RETPOLINE depend on compiler support")

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

> > ---

> >

> >   arch/x86/Makefile | 14 ++++++++------

> >   1 file changed, 8 insertions(+), 6 deletions(-)

> >

> > diff --git a/arch/x86/Makefile b/arch/x86/Makefile

> > index f5d7f41..ae0148b 100644

> > --- a/arch/x86/Makefile

> > +++ b/arch/x86/Makefile

> > @@ -219,12 +219,7 @@ KBUILD_CFLAGS += -Wno-sign-compare

> >   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

> > +KBUILD_CFLAGS += $(RETPOLINE_CFLAGS)

> >

> >   archscripts: scripts_basic

> >       $(Q)$(MAKE) $(build)=arch/x86/tools relocs

> > @@ -307,6 +302,13 @@ 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




--
Best Regards
Masahiro Yamada
Zhenzhong Duan Dec. 5, 2018, 6:07 a.m. UTC | #3 
On 2018/12/5 11:00, Masahiro Yamada wrote:
> It is wrong to add CONFIG option diagnostic to the Makefile parse

> stage.

>

> 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

> Reported-by: Meelis Roos <mroos@linux.ee>

> Fixes: 4cd24de3a098 ("x86/retpoline: Make CONFIG_RETPOLINE depend on compiler support")

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

> ---

>

>   arch/x86/Makefile | 14 ++++++++------

>   1 file changed, 8 insertions(+), 6 deletions(-)

>

> diff --git a/arch/x86/Makefile b/arch/x86/Makefile

> index f5d7f41..ae0148b 100644

> --- a/arch/x86/Makefile

> +++ b/arch/x86/Makefile

> @@ -219,12 +219,7 @@ KBUILD_CFLAGS += -Wno-sign-compare

>   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

> +KBUILD_CFLAGS += $(RETPOLINE_CFLAGS)


Is it better to also move "# Avoid indirect branches in kernel to deal 
with Spectre"

and "KBUILD_CFLAGS += $(RETPOLINE_CFLAGS)"?

Seems unconditionaly using "KBUILD_CFLAGS += $(RETPOLINE_CFLAGS)" will 
have compiler

using "__x86_indirect_thunk_\reg" call even ifCONFIG_RETPOLINE is 
disabled. I guess

link process will fail?

Thanks

Zhenzhong

>   

>   archscripts: scripts_basic

>   	$(Q)$(MAKE) $(build)=arch/x86/tools relocs

> @@ -307,6 +302,13 @@ 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
Masahiro Yamada Dec. 5, 2018, 6:10 a.m. UTC | #4 
On Wed, Dec 5, 2018 at 3:08 PM Zhenzhong Duan <zhenzhong.duan@oracle.com> wrote:
>

>

> On 2018/12/5 11:00, Masahiro Yamada wrote:

> > It is wrong to add CONFIG option diagnostic to the Makefile parse

> > stage.

> >

> > 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

> > Reported-by: Meelis Roos <mroos@linux.ee>

> > Fixes: 4cd24de3a098 ("x86/retpoline: Make CONFIG_RETPOLINE depend on compiler support")

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

> > ---

> >

> >   arch/x86/Makefile | 14 ++++++++------

> >   1 file changed, 8 insertions(+), 6 deletions(-)

> >

> > diff --git a/arch/x86/Makefile b/arch/x86/Makefile

> > index f5d7f41..ae0148b 100644

> > --- a/arch/x86/Makefile

> > +++ b/arch/x86/Makefile

> > @@ -219,12 +219,7 @@ KBUILD_CFLAGS += -Wno-sign-compare

> >   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

> > +KBUILD_CFLAGS += $(RETPOLINE_CFLAGS)

>

> Is it better to also move "# Avoid indirect branches in kernel to deal

> with Spectre"

>

> and "KBUILD_CFLAGS += $(RETPOLINE_CFLAGS)"?

>

> Seems unconditionaly using "KBUILD_CFLAGS += $(RETPOLINE_CFLAGS)" will

> have compiler

>

> using "__x86_indirect_thunk_\reg" call even ifCONFIG_RETPOLINE is

> disabled. I guess

>

> link process will fail?



Good catch.

I will send v2.

Thanks.



> Thanks

>

> Zhenzhong

>

> >

> >   archscripts: scripts_basic

> >       $(Q)$(MAKE) $(build)=arch/x86/tools relocs

> > @@ -307,6 +302,13 @@ 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




-- 
Best Regards
Masahiro Yamada
diff mbox series

Patch

diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index f5d7f41..ae0148b 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -219,12 +219,7 @@  KBUILD_CFLAGS += -Wno-sign-compare
 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
+KBUILD_CFLAGS += $(RETPOLINE_CFLAGS)
 
 archscripts: scripts_basic
 	$(Q)$(MAKE) $(build)=arch/x86/tools relocs
@@ -307,6 +302,13 @@  ifndef CC_HAVE_ASM_GOTO
 	@echo Compiler lacks asm-goto support.
 	@exit 1
 endif
+ifdef CONFIG_RETPOLINE
+ifeq ($(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