1. 前言
UBOOT版本：uboot2018.03，开发板myimx8mmek240。
2. 概述
在编译uboot的过程中，有两个特别的依赖version_h 和 timestamp_h，它们定义在顶层Makefile中（这里只讲解编译直接在源目录的情况，即srctree 为空），如下：
# 顶层Makefile
version_h := include/generated/version_autogenerated.h
timestamp_h := include/generated/timestamp_autogenerated.h
......
$(version_h): include/config/uboot.release FORCE
$(call filechk,version.h)
$(timestamp_h): $(srctree)/Makefile FORCE
$(call filechk,timestamp.h)
3. 目标$(version_h)
# 顶层Makefile
$(version_h): include/config/uboot.release FORCE
$(call filechk,version.h)
3.1 $(version_h)依赖分析
3.1.1 依赖include/config/uboot.release
使用scripts/setlocalversion工具来生成include/config/uboot.release，只是一个版本号，不需要特别关注，参见LINUX 内核编译 LOCALVERSION 配置(分析内核版本号自动添加的"+"号)。
# 顶层Makefile
# Store (new) UBOOTRELEASE string in include/config/uboot.release
include/config/uboot.release: include/config/auto.conf FORCE
$(call filechk,uboot.release)
include/config/uboot.release定义在顶层Makefile中，该目标又依赖于include/config/auto.conf（参见UBOOT编译--- include/config/auto.conf、 include/config/auto.conf.cmd、 include/generated/autoconf.h (二)） 和 FORCE。
接下来我们看规则$(call filechk,uboot.release)：
#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/config/uboot.release ；
‘$(1)’ ：第一个参数uboot.release；
‘$ <’ ：第一个依赖include/config/auto.conf ；
‘filechk_$(1)’ ：filechk_uboot.release；
filechk_uboot.release定义在顶层Makefile中：
#note：顶层Makefile
# Read UBOOTRELEASE from include/config/uboot.release (if it exists)
UBOOTRELEASE = $(shell cat include/config/uboot.release 2> /dev/null)
UBOOTVERSION = $(VERSION)$(if $(PATCHLEVEL),.$(PATCHLEVEL)$(if $(SUBLEVEL),.$(SUBLEVEL)))$(EXTRAVERSION)
......
define filechk_uboot.release
echo "$(UBOOTVERSION)$$($(CONFIG_SHELL) $(srctree)/scripts/setlocalversion $(srctree))"
endef
全部展开，具体编译命令如下：
set -e; : ' CHK include/config/uboot.release'; mkdir -p include/config/; echo "2018.03$(/bin/sh ./scripts/setlocalversion .)" < include/config/auto.conf > include/config/uboot.release.tmp; if [ -r include/config/uboot.release ] && cmp -s include/config/uboot.release include/config/uboot.release.tmp; then rm -f include/config/uboot.release.tmp; else : ' UPD include/config/uboot.release'; mv -f include/config/uboot.release.tmp include/config/uboot.release; fi
最终产生的include/config/uboot.release内容如下：
3.1.2 依赖FORCE
参见UBOOT编译--- make xxx_deconfig过程详解(一) 4.3小节 - 依赖 FORCE。
3.2 $(version_h)规则分析
接下来我们看规则$(call filechk,version.h)：
#note：scripts/Kbuild.include
###
# filechk is used to check if the content of a generated file is updated.
# Sample usage:
# define filechk_sample
# echo $KERNELRELEASE
# endef
# version.h : Makefile
# $(call filechk,sample)
# The rule defined shall write to stdout the content of the new file.
# The existing file will be compared with the new one.
# - If no file exist it is created
# - If the content differ the new file is used
# - If they are equal no change, and no timestamp update
# - stdin is piped in from the first prerequisite ($<) so one has
# to specify a valid file as first prerequisite (often the kbuild file)
define filechk
$(Q)set -e; \
$(kecho) ' CHK $@'; \
mkdir -p $(dir $@); \
$(filechk_$(1)) < $< > $@.tmp; \
if [ -r $@ ] && cmp -s $@ $@.tmp; then \
rm -f $@.tmp; \
else \
$(kecho) ' UPD $@'; \
mv -f $@.tmp $@; \
fi
endef
上述代码中：
‘$@’ ：目标include/generated/version_autogenerated.h；
‘$(1)’ ：第一个参数version.h；
‘$ <’ ：第一个依赖include/config/uboot.release；
‘filechk_$(1)’ ：filechk_version.h；
filechk_version.h定义在顶层Makefile中：
#note：顶层Makefile
define filechk_version.h
(echo \#define PLAIN_VERSION \"$(UBOOTRELEASE)\"; \
echo \#define U_BOOT_VERSION \"U-Boot \" PLAIN_VERSION; \
echo \#define CC_VERSION_STRING \"$$(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
include/generated/version_autogenerated.h内容如下：
4. 目标$(timestamp_h)
# 顶层Makefile
$(timestamp_h): $(srctree)/Makefile FORCE
$(call filechk,timestamp.h)
4.1 $(timestamp_h)依赖分析
目标 timestamp_h依赖$(srctree)/Makefile 和FORCE。假设直接在源目录编译，顶层Makefile存在，依赖FORCE见UBOOT编译--- make xxx_deconfig过程详解(一) 4.3小节 - 依赖 FORCE。
4.2 $(timestamp_h)规则分析
接下来我们看规则$(call filechk,timestamp.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timestamp_h (include/generated/timestamp_autogenerated.h)；
‘$(1)’ ：第一个参数timestamp.h；
‘$ <’ ：第一个依赖$(srctree)/Makefile ；
‘filechk_$(1)’ ：filechk_timestamp.h；
filechk_timestamp.h定义在顶层Makefile中：
#note：顶层Makefile
define filechk_timestamp.h
(if test -n "$${SOURCE_DATE_EPOCH}"; then \
SOURCE_DATE="@$${SOURCE_DATE_EPOCH}"; \
DATE=""; \
for date in gdate date.gnu date; do \
$${date} -u -d "$${SOURCE_DATE}" >/dev/null 2>&1 && DATE="$${date}"; \
done; \
if test -n "$${DATE}"; then \
LC_ALL=C $${DATE} -u -d "$${SOURCE_DATE}" +'#define U_BOOT_DATE "%b %d %C%y"'; \
LC_ALL=C $${DATE} -u -d "$${SOURCE_DATE}" +'#define U_BOOT_TIME "%T"'; \
LC_ALL=C $${DATE} -u -d "$${SOURCE_DATE}" +'#define U_BOOT_TZ "%z"'; \
LC_ALL=C $${DATE} -u -d "$${SOURCE_DATE}" +'#define U_BOOT_DMI_DATE "%m/%d/%Y"'; \
LC_ALL=C $${DATE} -u -d "$${SOURCE_DATE}" +'#define U_BOOT_BUILD_DATE 0x%Y%m%d'; \
else \
return 42; \
fi; \
else \
LC_ALL=C date +'#define U_BOOT_DATE "%b %d %C%y"'; \
LC_ALL=C date +'#define U_BOOT_TIME "%T"'; \
LC_ALL=C date +'#define U_BOOT_TZ "%z"'; \
LC_ALL=C date +'#define U_BOOT_DMI_DATE "%m/%d/%Y"'; \
LC_ALL=C date +'#define U_BOOT_BUILD_DATE 0x%Y%m%d'; \
fi)
endef
这上面首先判断在环境变量中是否定义了 SOURCE_DATE_EPOCH ，有则使用 SOURCE_DATE_EPOCH 生成时间戳，没有则使用当前时间。有些编译环境会设置，这个目前我所了解的作用是保证uboot二进制一致性会用到(有机会我们后面会针对镜像二进制一致性单独写一篇)。LC_ALL=C 是为了去除所有本地化的设置，让命令能正确执行。date命令的功能是显示和设置系统日期和时间，使用规则可以参见：linux date命令。在我所使用的的平台暂时没有定义，因此走else分支。整个命令的流程如下：
（1）打印 ' CHK include/generated/timestamp_autogenerated.h'；
（2）创建include/generated/目录；
（3）通过date命令，定义几个宏定义，并输出到include/generated/timestamp_autogenerated.h.tmp中；
（4）如果include/generated/timestamp_autogenerated.h 文件存在，且与include/generated/timestamp_autogenerated.h.tmp相同，则直接删除include/generated/timestamp_autogenerated.h.tmp；
（5）如果4不成立，打印' UPD include/generated/timestamp_autogenerated.h'，并把include/generated/timestamp_autogenerated.h.tmp更名为include/generated/timestamp_autogenerated.h。
使用cmp命令比较include/generated/timestamp_autogenerated.h include/generated/timestamp_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/timestamp_autogenerated.h'; mkdir -p include/generated/; (if test -n "${SOURCE_DATE_EPOCH}"; then SOURCE_DATE="@${SOURCE_DATE_EPOCH}"; DATE=""; for date in gdate date.gnu date; do ${date} -u -d "${SOURCE_DATE}" >/dev/null 2>&1 && DATE="${date}"; done; if test -n "${DATE}"; then LC_ALL=C ${DATE} -u -d "${SOURCE_DATE}" +'#define U_BOOT_DATE "%b %d %C%y"'; LC_ALL=C ${DATE} -u -d "${SOURCE_DATE}" +'#define U_BOOT_TIME "%T"'; LC_ALL=C ${DATE} -u -d "${SOURCE_DATE}" +'#efine U_BOOT_TZ "%z"'; LC_ALL=C ${DATE} -u -d "${SOURCE_DATE}" +'#define U_BOOT_DMI_DATE "%m/%d/%Y"'; LC_ALL=C ${DATE} -u -d "${SOURCE_DATE}" +'#define U_BOOT_BUILD_DATE 0x%Y%m%d'; else return 42; fi; else LC_ALL=C date +'#define U_BOOT_DATE "%b %d %C%y"'; LC_ALL=C date +'#define U_BOOT_TIME "%T"'; LC_ALL=C date +'#define U_BOOT_TZ "%z"'; LC_ALL=C date +'#define U_BOOT_DMI_DATE "%m/%d/%Y"'; LC_ALL=C date +'#define U_BOOT_BUILD_DATE 0x%Y%m%d'; fi) < Makefile > include/generated/timestamp_autogenerated.h.tmp; if [ -r include/generated/timestamp_autogenerated.h ] && cmp -s include/generated/timestamp_autogenerated.h include/generated/timestamp_autogenerated.h.tmp; then rm -f include/generated/timestamp_autogenerated.h.tmp; else : ' UPD include/generated/timestamp_autogenerated.h'; mv -f include/generated/timestamp_autogenerated.h.tmp include/generated/timestamp_autogenerated.h; fi
include/generated/timestamp_autogenerated.h内容如下：
![2022-11-08：以下go语言代码输出什么？A：2；B：编译错误；C：运行 panic。 package main import “fmt“ func main() { a := []int](https://www.kunjuke.com/file/css/thumb/2.jpg/280-180.jpg)
