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 <[email protected]>
Fixes: 4cd24de3a098 ("x86/retpoline: Make CONFIG_RETPOLINE depend on compiler support")
Signed-off-by: Masahiro Yamada <[email protected]>
---
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 $(objtree)/arch/i386
--
2.7.4
Hi Masahiro,
Thanks for fixing.
There is a question still confusing me. There are many CONFIG_* used in
arch/x86/Makefile.
Will they also be impacted or not?
# grep CONFIG_ arch/x86/Makefile
ifeq ($(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 ($(CONFIG_X86_DECODER_SELFTEST),y)
Thanks
Zhenzhong
On 2018/12/5 11:00, Masahiro Yamada wrote:
> It is wrong to add CONFIG option diagnostic to the Makefile parse
> stage.
>
> Once you are hit by the error about non-retpoline compiler, the
> compilation still breaks even after disabling CONFIG_RETPOLINE.
>
> The easiest fix is to move this check to the "archprepare" like commit
> 829fe4aa9ac1 ("x86: Allow generating user-space headers without a
> compiler") did.
>
> Link: https://lkml.org/lkml/2018/12/4/206
> Reported-by: Meelis Roos <[email protected]>
> Fixes: 4cd24de3a098 ("x86/retpoline: Make CONFIG_RETPOLINE depend on compiler support")
> Signed-off-by: Masahiro Yamada <[email protected]>
> ---
>
> arch/x86/Makefile | 14 ++++++++------
> 1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> index f5d7f41..ae0148b 100644
> --- a/arch/x86/Makefile
> +++ b/arch/x86/Makefile
> @@ -219,12 +219,7 @@ KBUILD_CFLAGS += -Wno-sign-compare
> KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
>
> # Avoid indirect branches in kernel to deal with Spectre
> -ifdef CONFIG_RETPOLINE
> -ifeq ($(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
On Wed, Dec 5, 2018 at 12:23 PM Zhenzhong Duan
<[email protected]> 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 ($(CONFIG_X86_DECODER_SELFTEST),y)
>
> Thanks
> Zhenzhong
> On 2018/12/5 11:00, Masahiro Yamada wrote:
> > It is wrong to add CONFIG option diagnostic to the Makefile parse
> > stage.
> >
> > Once you are hit by the error about non-retpoline compiler, the
> > compilation still breaks even after disabling CONFIG_RETPOLINE.
> >
> > The easiest fix is to move this check to the "archprepare" like commit
> > 829fe4aa9ac1 ("x86: Allow generating user-space headers without a
> > compiler") did.
> >
> > Link: https://lkml.org/lkml/2018/12/4/206
> > Reported-by: Meelis Roos <[email protected]>
> > Fixes: 4cd24de3a098 ("x86/retpoline: Make CONFIG_RETPOLINE depend on compiler support")
> > Signed-off-by: Masahiro Yamada <[email protected]>
> > ---
> >
> > arch/x86/Makefile | 14 ++++++++------
> > 1 file changed, 8 insertions(+), 6 deletions(-)
> >
> > diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> > index f5d7f41..ae0148b 100644
> > --- a/arch/x86/Makefile
> > +++ b/arch/x86/Makefile
> > @@ -219,12 +219,7 @@ KBUILD_CFLAGS += -Wno-sign-compare
> > KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
> >
> > # Avoid indirect branches in kernel to deal with Spectre
> > -ifdef CONFIG_RETPOLINE
> > -ifeq ($(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 $(objtree)/arch/i386
--
Best Regards
Masahiro Yamada
On 2018/12/5 11:00, Masahiro Yamada wrote:
> It is wrong to add CONFIG option diagnostic to the Makefile parse
> stage.
>
> Once you are hit by the error about non-retpoline compiler, the
> compilation still breaks even after disabling CONFIG_RETPOLINE.
>
> The easiest fix is to move this check to the "archprepare" like commit
> 829fe4aa9ac1 ("x86: Allow generating user-space headers without a
> compiler") did.
>
> Link: https://lkml.org/lkml/2018/12/4/206
> Reported-by: Meelis Roos <[email protected]>
> Fixes: 4cd24de3a098 ("x86/retpoline: Make CONFIG_RETPOLINE depend on compiler support")
> Signed-off-by: Masahiro Yamada <[email protected]>
> ---
>
> arch/x86/Makefile | 14 ++++++++------
> 1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> index f5d7f41..ae0148b 100644
> --- a/arch/x86/Makefile
> +++ b/arch/x86/Makefile
> @@ -219,12 +219,7 @@ KBUILD_CFLAGS += -Wno-sign-compare
> KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
>
> # Avoid indirect branches in kernel to deal with Spectre
> -ifdef CONFIG_RETPOLINE
> -ifeq ($(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 $(objtree)/arch/i386
On Wed, Dec 5, 2018 at 3:08 PM Zhenzhong Duan <[email protected]> wrote:
>
>
> On 2018/12/5 11:00, Masahiro Yamada wrote:
> > It is wrong to add CONFIG option diagnostic to the Makefile parse
> > stage.
> >
> > Once you are hit by the error about non-retpoline compiler, the
> > compilation still breaks even after disabling CONFIG_RETPOLINE.
> >
> > The easiest fix is to move this check to the "archprepare" like commit
> > 829fe4aa9ac1 ("x86: Allow generating user-space headers without a
> > compiler") did.
> >
> > Link: https://lkml.org/lkml/2018/12/4/206
> > Reported-by: Meelis Roos <[email protected]>
> > Fixes: 4cd24de3a098 ("x86/retpoline: Make CONFIG_RETPOLINE depend on compiler support")
> > Signed-off-by: Masahiro Yamada <[email protected]>
> > ---
> >
> > arch/x86/Makefile | 14 ++++++++------
> > 1 file changed, 8 insertions(+), 6 deletions(-)
> >
> > diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> > index f5d7f41..ae0148b 100644
> > --- a/arch/x86/Makefile
> > +++ b/arch/x86/Makefile
> > @@ -219,12 +219,7 @@ KBUILD_CFLAGS += -Wno-sign-compare
> > KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
> >
> > # Avoid indirect branches in kernel to deal with Spectre
> > -ifdef CONFIG_RETPOLINE
> > -ifeq ($(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