make V=1 分析

make V=1

# 顶层 Makefile
580 -include include/config/auto.conf
584 -include include/config/auto.conf.cmd
......
593 include/config/%.conf: $(KCONFIG_CONFIG) include/config/auto.conf.cmd
594 	$(Q)$(MAKE) -f $(srctree)/Makefile syncconfig
595	    @# If the following part fails, include/config/auto.conf should be
596	    @# deleted so "make silentoldconfig" will be re-run on the next build.
597	    $(Q)$(MAKE) -f $(srctree)/scripts/Makefile.autoconf || \
598		       { rm -f include/config/auto.conf; false; }
599	    @# include/config.h has been updated after "make silentoldconfig".
600     @# We need to touch include/config/auto.conf so it gets newer
601 	@# than include/config.h.
602 	@# Otherwise, 'make silentoldconfig' would be invoked twice.
603 	$(Q)touch include/config/auto.conf