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SubjectRe: [Regression 4.15] Can't kill CONFIG_UNWINDER_ORC with fire or plague.
On Thu, Dec 28, 2017 at 09:13:24PM -0500, Paul Gortmaker wrote:
> > > There is a regression new to 4.15 that happens in a rather common
> > > workflow which results in the frustrating situation where the user has
> > > clearly disabled UNWINDER_ORC in their ".config" file, and yet they
> > > still get the immediate false error saying they need libelf-dev since
> > > "CONFIG_UNWINDER_ORC=y" is still set, and hence they can not build.
> > >
> > > The regression requires UNWINDER_ORC=y (now the default in commit
> > > fc72ae40e303) followed by the user subsequently disabling it, which is
> > > common if the user doesn't have libelf-dev and doesn't care about ORC.
> > >
> > > This happens because the recently added test in the top level Makefile
> > > assumes that ,config data will be mapped into include/config/auto.conf
> > > either by the end user running "make oldconfig" or the Makefile itself
> > > detecting that "silentoldconfig" should be run. As the simple
> > > reproducer below shows, this clearly does not happen as expected.

This seems to be related to a kconfig quirk where only silentoldconfig
updates the include/config/auto.conf file. The other config targets
(oldconfig, defconfig, etc) don't touch it. It seems intentional, but I
have no idea why.

That causes the Makefile to get stale data for 'CONFIG_*' variables when
it includes auto.conf. So I don't think this is specific to the ORC
check. It seems like it could also cause bugs elsewhere.

The below (ugly) patch fixes it, though I'm not sure this is the best
way to do it. We probably need Masahiro or Michal to chime in here.

diff --git a/scripts/kconfig/Makefile b/scripts/kconfig/Makefile
index 297c1bf35140..3a0d92040a9c 100644
--- a/scripts/kconfig/Makefile
+++ b/scripts/kconfig/Makefile
@@ -21,18 +21,23 @@ unexport CONFIG_

xconfig: $(obj)/qconf
$< $(silent) $(Kconfig)
+ $(Q)$(MAKE) -f $(srctree)/Makefile silentoldconfig

gconfig: $(obj)/gconf
$< $(silent) $(Kconfig)
+ $(Q)$(MAKE) -f $(srctree)/Makefile silentoldconfig

menuconfig: $(obj)/mconf
$< $(silent) $(Kconfig)
+ $(Q)$(MAKE) -f $(srctree)/Makefile silentoldconfig

config: $(obj)/conf
$< $(silent) --oldaskconfig $(Kconfig)
+ $(Q)$(MAKE) -f $(srctree)/Makefile silentoldconfig

nconfig: $(obj)/nconf
$< $(silent) $(Kconfig)
+ $(Q)$(MAKE) -f $(srctree)/Makefile silentoldconfig

silentoldconfig: $(obj)/conf
$(Q)mkdir -p include/config include/generated
@@ -85,6 +90,7 @@ PHONY += $(simple-targets)

$(simple-targets): $(obj)/conf
$< $(silent) --$@ $(Kconfig)
+ $(Q)$(MAKE) -f $(srctree)/Makefile silentoldconfig

PHONY += oldnoconfig savedefconfig defconfig

@@ -108,9 +114,11 @@ else
$(Q)$(MAKE) -f $(srctree)/Makefile $(KBUILD_DEFCONFIG)
+ $(Q)$(MAKE) -f $(srctree)/Makefile silentoldconfig

%_defconfig: $(obj)/conf
$(Q)$< $(silent) --defconfig=arch/$(SRCARCH)/configs/$@ $(Kconfig)
+ $(Q)$(MAKE) -f $(srctree)/Makefile silentoldconfig

configfiles=$(wildcard $(srctree)/kernel/configs/$@ $(srctree)/arch/$(SRCARCH)/configs/$@)

@@ -118,6 +126,7 @@ configfiles=$(wildcard $(srctree)/kernel/configs/$@ $(srctree)/arch/$(SRCARCH)/c
$(if $(call configfiles),, $(error No configuration exists for this target on this architecture))
$(Q)$(CONFIG_SHELL) $(srctree)/scripts/kconfig/ -m .config $(configfiles)
+$(Q)yes "" | $(MAKE) -f $(srctree)/Makefile oldconfig
+ $(Q)$(MAKE) -f $(srctree)/Makefile silentoldconfig

PHONY += kvmconfig
kvmconfig: kvm_guest.config
@@ -130,6 +139,7 @@ xenconfig: xen.config
PHONY += tinyconfig
$(Q)$(MAKE) -f $(srctree)/Makefile allnoconfig tiny.config
+ $(Q)$(MAKE) -f $(srctree)/Makefile silentoldconfig

# Help text used by make help
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