[PATCH] build/xen: fail to rebuild if Kconfig fails

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

When doing a rebuild with an xen/include/config/auto.conf already present in
the tree, failures from Kconfig are ignored since the target is present:

gmake -C xen install
gmake[1]: Entering directory '/root/src/xen/xen'
tools/kconfig/conf  --syncconfig Kconfig
common/Kconfig:2: syntax error
common/Kconfig:1: invalid statement
gmake[2]: *** [tools/kconfig/Makefile:73: syncconfig] Error 1
  UPD     include/xen/compile.h
 Xen 4.19-unstable
gmake[3]: Nothing to be done for 'all'.
gmake[2]: 'arch/x86/include/asm/asm-offsets.h' is up to date.

Ultimately leading to a successful build despite the Kconfig error.

Fix this by first removing xen/include/config/auto.conf before attempting to
regenerate, and then also make xen/include/config/auto.conf a hard dependency
of the build process (ie: drop the leading '-') and reordering so the .cmd
target is executed before including the configuration file.

This leads to the build properly failing if the config file cannot be
re-generated:

gmake -C xen install
gmake[1]: Entering directory '/root/src/xen/xen'
rm -rf include/config/auto.conf
tools/kconfig/conf  --syncconfig Kconfig
common/Kconfig:2: syntax error
common/Kconfig:1: invalid statement
gmake[2]: *** [tools/kconfig/Makefile:73: syncconfig] Error 1
gmake[1]: *** [Makefile:379: include/config/auto.conf] Error 2
gmake[1]: Leaving directory '/root/src/xen/xen'
gmake: *** [Makefile:143: install-xen] Error 2

Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
Maybe there's a better way for dealing with all this, my makefile foo is very
limited.
---
 xen/Makefile | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/xen/Makefile b/xen/Makefile
index 21832d640225..7e6860a58a1d 100644
--- a/xen/Makefile
+++ b/xen/Makefile
@@ -358,10 +358,10 @@ config: tools_fixdep outputmakefile FORCE
 else # !config-build
 
 ifeq ($(need-config),y)
--include include/config/auto.conf
 # Read in dependencies to all Kconfig* files, make sure to run syncconfig if
 # changes are detected.
 -include include/config/auto.conf.cmd
+include include/config/auto.conf
 
 # Allow people to just run `make` as before and not force them to configure
 # Only run defconfig if $(KCONFIG_CONFIG) is missing
@@ -375,6 +375,7 @@ $(KCONFIG_CONFIG): tools_fixdep
 # This exploits the 'multi-target pattern rule' trick.
 # The syncconfig should be executed only once to make all the targets.
 include/config/%.conf include/config/%.conf.cmd: $(KCONFIG_CONFIG)
+       rm -rf include/config/$*.conf
        $(Q)$(MAKE) $(build)=tools/kconfig syncconfig
 
 ifeq ($(CONFIG_DEBUG),y)
-- 
2.43.0