接下来我们看规则$(call filechk,version.h)：

#note：scripts/Kbuild.include
###
# filechk is used to check if the content of a generated file is updated.
# Sample usage:
# define filechk_sample
#	echo $KERNELRELEASE
# endef
# version.h : Makefile
#	$(call filechk,sample)
# The rule defined shall write to stdout the content of the new file.
# The existing file will be compared with the new one.
# - If no file exist it is created
# - If the content differ the new file is used
# - If they are equal no change, and no timestamp update
# - stdin is piped in from the first prerequisite ($<) so one has
#   to specify a valid file as first prerequisite (often the kbuild file)
define filechk
	$(Q)set -e;				\
	$(kecho) '  CHK     $@';		\
	mkdir -p $(dir $@);			\
	$(filechk_$(1)) < $< > $@.tmp;		\
	if [ -r $@ ] && cmp -s $@ $@.tmp; then	\
		rm -f $@.tmp;			\
	else					\
		$(kecho) '  UPD     $@';	\
		mv -f $@.tmp $@;		\
	fi
endef

上述代码中：

• ‘$@’ ：目标include/generated/version_autogenerated.h；
• ‘$(1)’ ：第一个参数version.h；
• ‘$ <’ ：第一个依赖include/config/uboot.release；
• ‘filechk_$(1)’ ：filechk_version.h；
  
  

filechk_version.h定义在顶层Makefile中：

#note：顶层Makefile
define filechk_version.h
	(echo \#define PLAIN_VERSION \"$(UBOOTRELEASE)\"; \
	echo \#define U_BOOT_VERSION \"U-Boot \" PLAIN_VERSION; \
	echo \#define CC_VERSION_STRING \"$$(LC_ALL=C $(CC) --version | head -n 1)\"; \
	echo \#define LD_VERSION_STRING \"$$(LC_ALL=C $(LD) --version | head -n 1)\"; )
endef

这上面主要时输出uboot版本和编译器版本。整个命令的流程如下：
（1）打印 ' CHK include/generated/version_autogenerated.h'；
（2）创建include/generated/目录；
（3）输出指定信息到include/generated/version_autogenerated.h中；
（4）如果include/generated/version_autogenerated.h 文件存在，且与include/generated/version_autogenerated.h.tmp相同，则直接删除include/generated/version_autogenerated.h.tmp；
（5）如果4不成立，打印' UPD include/generated/version_autogenerated.h'，并把include/generated/version_autogenerated.h.tmp更名为include/generated/version_autogenerated.h。

使用cmp命令比较include/generated/version_autogenerated.h include/generated/version_autogenerated.h.tmp两个文件(Linux中的cmp命令用于比较两个文件的不同，若发现两个文件有不同支出，则会标出来第一处不同的位置和列数编号；s或--quiet或--silent: 不显示错误信息)

全部展开，具体编译命令如下：

set -e; : '  CHK     include/generated/version_autogenerated.h'; mkdir -p include/generated/;   (echo \#define PLAIN_VERSION \"2018.03""\"; echo \#define U_BOOT_VERSION \"U-Boot \" PLAIN_VERSION; echo \#define CC_VERSION_STRING \"$(LC_ALL=C /home/h/my-work/03_toolchain/gcc-linaro-7.3.1-2018.05-x86_64_aarch64-linux-gnu/bin/aarch64-linux-gnu-gcc --version | head -n 1)\"; echo \#define LD_VERSION_STRING \"$(LC_ALL=C /home/h/my-work/03_toolchain/gcc-linaro-7.3.1-2018.05-x86_64_aarch64-linux-gnu/bin/aarch64-linux-gnu-ld.bfd --version | head -n 1)\"; ) < include/config/uboot.release > include/generated/version_autogenerated.h.tmp; if [ -r include/generated/version_autogenerated.h ] && cmp -s include/generated/version_autogenerated.h include/generated/version_autogenerated.h.tmp; then rm -f include/generated/version_autogenerated.h.tmp; else : '  UPD     include/generated/version_autogenerated.h'; mv -f include/generated/version_autogenerated.h.tmp include/generated/version_autogenerated.h; fi