Having a direct dependency Makefile: $(GENERATED_HEADERS) can result in not-from-clean builds failing sometimes, because it means that when Make does its "is any makefile or include out of date and needing a rebuild?" check, as well as possibly running configure (to update config-host.mak) it will also rebuild GENERATED_HEADERS under the "old" config-host.mak regime. If the makefile rules for rebuilding the generated headers have changed in a way that means they're not compatible with the old config-host.mak variable names, the build will fail. Even if it does work, it's wasted effort since we'll need to rebuild them with the right config-host.mak settings immediately.
Instead, make the generated headers depend on config-host.mak and config-target.mak. This means we'll definitely rebuild them if the configuration changes, but it will be done after Make reloads its makefiles and includes so will happen with the correct set of config-host.mak settings. We rely on the various .o files having correct autogenerated dependency rules to cause the generated headers to be generated as and when they are needed. Signed-off-by: Peter Maydell <peter.mayd...@linaro.org> --- The specific example of this is the change from CONFIG_TRACE_BACKEND to CONFIG_TRACE_BACKENDS, which I am still hitting on a pretty regular basis. This patch fixes that problem and I don't think it has any unpleasant side effects; Paolo, have I missed anything? Makefile | 8 +++----- Makefile.target | 2 +- 2 files changed, 4 insertions(+), 6 deletions(-) diff --git a/Makefile b/Makefile index 145adb6..dca33b4 100644 --- a/Makefile +++ b/Makefile @@ -546,11 +546,9 @@ ifdef SIGNCODE endif # SIGNCODE endif # CONFIG_WIN -# Add a dependency on the generated files, so that they are always -# rebuilt before other object files -ifneq ($(filter-out %clean,$(MAKECMDGOALS)),$(if $(MAKECMDGOALS),,fail)) -Makefile: $(GENERATED_HEADERS) -endif +# Make the generated files depend on config-host.mak so that if +# the configuration settings change we will rebuild them +$(GENERATED_HEADERS): config-host.mak # Include automatically generated dependency files # Dependencies in Makefile.objs files come from our recursive subdir rules diff --git a/Makefile.target b/Makefile.target index 6089d29..ea8614a 100644 --- a/Makefile.target +++ b/Makefile.target @@ -198,4 +198,4 @@ ifdef CONFIG_TRACE_SYSTEMTAP endif GENERATED_HEADERS += config-target.h -Makefile: $(GENERATED_HEADERS) +$(GENERATED_HEADERS): config-target.mak config-devices.mak -- 2.0.0
