UBOOT编译--- make xxx_deconfig过程详解(一)

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make xxx_deconfig过程详解

• 1. 前言
• 2. 概述
• 3. build变量的定义
• 4. 目标%config的定义
• • 4.1 依赖 scripts_basic
    • • 4.1.1 语句$(if $ (KBUILD_BUILTIN),$(builtin-target) $(lib-target) $(extra-y))
        • 4.1.2 语句 $(if $ (KBUILD_MODULES),$(obj-m) $(modorder-target))*
        • 4.1.3 $(subdir-ym)
        • 4.1.4 $(always) 重点关注
        • • 4.1.4.1 src的定义
            • 4.1.4.2 kbuild-dir的定义
            • 4.1.4.3 kbuild-file的定义
            • 4.1.4.4 又在Makefile.build中包含include scripts/Makefile.lib
    • 4.2 依赖 outputmakefile
    • 4.3 依赖 FORCE
    • 4.4 规则 $ (Q)$(MAKE) $(build)=scripts/kconfig $@
• 5 总结

1. 前言

UBOOT版本：uboot2018.03，开发板myimx8mmek240。

2. 概述

Ubootb编译第一步通常是执行make xxx_config，在编译指定顶层目录生成.config文件，这种方式要求厂商提供一个基础的xxx_config文件(通常来说开发者不会通过执行make menuconfig从零开始配置，这个工作过量太大了)。本文接下来的章节主要解析这条指令背后主要做了什么。我是用的开发板执行命令为：make myimx8mmek240-8mm-2g_defconfig

3. build变量的定义

在scripts/Kbuild.include 中定义：

|  | ### |
|  | # Shorthand for $(Q)$(MAKE) -f scripts/Makefile.build obj= |
|  | # Usage: |
|  | # $(Q)$(MAKE) $(build)=dir |
|  | build := -f $(srctree)/scripts/Makefile.build obj |

4. 目标%config的定义

在顶层Makefile中定义：

|  | # We need some generic definitions (do not try to remake the file). |
|  | scripts/Kbuild.include: ; |
|  | include scripts/Kbuild.include //注意这个引用 |
|  |  |
|  | ...... |
|  |  |
|  | config: scripts\_basic outputmakefile FORCE |
|  |  $(Q)$(MAKE) $(build)=scripts/kconfig $@ |
|  |  |
|  | %config: scripts\_basic outputmakefile FORCE |
|  |  $(Q)$(MAKE) $(build)=scripts/kconfig $@ |

4.1 依赖 scripts_basic

（参考：linux内核Makefile中的变量build— 过渡篇（五））

|  | # 顶层Makefile |
|  | # Basic helpers built in scripts/ |
|  | PHONY += scripts\_basic |
|  | scripts\_basic: |
|  |  $(Q)$(MAKE) $(build)=scripts/basic |
|  |  $(Q)rm -f .tmp\_quiet\_recordmcount |

展开变量build

|  | # 顶层Makefile |
|  | # Basic helpers built in scripts/ |
|  | PHONY += scripts\_basic |
|  | scripts\_basic: |
|  |  $(Q)$(MAKE) -f $(srctree)/scripts/Makefile.build obj=scripts/basic |
|  |  $(Q)rm -f .tmp\_quiet\_recordmcount |

make -f $(srctree)/scripts/Makefile.build obj=scripts/basic的解析如下：

这是一种不指定目标的情况，由于未指定目标，这时会使用Makefile.build中的默认目标__build。然后更进一步，会使用$(obj)/Makefile(scripts/basic/Makefile)中定义的变量来进行目标匹配。
__build在Makefile.build中的构建规则为：

|  | \_\_build: $(if $(KBUILD\_BUILTIN),$(builtin-target) $(lib-target) $(extra-y)) \ |
|  |  $(if $(KBUILD\_MODULES),$(obj-m) $(modorder-target)) \ |
|  |  $(subdir-ym) $(always) |
|  |  @: |

4.1.1 语句$(if $ (KBUILD_BUILTIN),$(builtin-target) $(lib-target) $(extra-y))

在顶层Makefile中，KBUILD_BUILTIN的定义如下：

|  | # note：顶层Makefile |
|  |  KBUILD\_BUILTIN := 1 |
|  |  export KBUILD\_MODULES KBUILD\_BUILTIN |

该语句展开为：

|  | $(builtin-target) $(lib-target) $(extra-y) |

（1）lib-target

|  | # note：顶层Makefile |
|  | ifneq ($(strip $(lib-y) $(lib-m) $(lib-)),) |
|  |  lib-target := $(obj)/lib.a |
|  | endif  |

在此语句之前obj-y := ;obj-m := ;obj-未定义。因此lib-target为空。

（2）builtin-target ​​​​​​​

|  | # note：顶层Makefile |
|  | ifneq ($(strip $(obj-y) $(obj-m) $(obj-) $(subdir-m) $(lib-target)),) |
|  |  builtin-target := $(obj)/built-in.o |
|  | endif |

在此语句之前obj-y := ; obj-m := ;obj-未定义 ; subdir-m := ;并且在所包含的文件中也没有给这些变量增加值。lib-target 为空。因此builtin-target为空。

（3）extra-y未定义 综上：语句$(if $ (KBUILD_BUILTIN),$(builtin-target) $(lib-target) $(extra-y))为空。

4.1.2 语句 $(if $ (KBUILD_MODULES),$(obj-m) $(modorder-target))*

在顶层Makefile中，KBUILD_BUILTIN的定义如下：

|  | # note：顶层Makefile |
|  | KBUILD\_MODULES := |

综上：语句$(if $ (KBUILD_MODULES),$(obj-m) $(modorder-target))为空。

4.1.3 $(subdir-ym)

在scripts/Makefile.lib中，subdir-ym的定义如下：

|  | # note：scripts/Makefile.lib |
|  | # Subdirectories we need to descend into |
|  | subdir-ym := $(sort $(subdir-y) $(subdir-m)) |
|  | ...... |
|  | subdir-ym := $(addprefix $(obj)/,$(subdir-ym)) |

subdir-y与subdir-m都为空。 综上：语句$(subdir-ym)为空。

4.1.4 $(always) 重点关注

在scripts/Makefile.build有如下定义

|  | # note：scripts/Makefile.build |
|  | # The filename Kbuild has precedence over Makefile |
|  | kbuild-dir := $(if $(filter /%,$(src)),$(src),$(srctree)/$(src)) |
|  | kbuild-file := $(if $(wildcard $(kbuild-dir)/Kbuild),$(kbuild-dir)/Kbuild,$(kbuild-dir)/Makefile) |
|  | include $(kbuild-file) |

4.1.4.1 src的定义

在scripts/Makefile.build有如下定义

|  | # note：scripts/Makefile.build |
|  | # Modified for U-Boot |
|  | prefix := tpl |
|  | src := $(patsubst $(prefix)/%,%,$(obj)) |
|  | ifeq ($(obj),$(src)) |
|  | prefix := spl |
|  | src := $(patsubst $(prefix)/%,%,$(obj)) |
|  | ifeq ($(obj),$(src)) |
|  | prefix := . |
|  | endif |
|  | endif |

在命令make -f ./scripts/Makefile.build obj=scripts/basic我们传入了obj=scripts/basic 所以src = obj = scripts/basic, prefix := .

4.1.4.2 kbuild-dir的定义

在scripts/Makefile.build有如下定义

|  | kbuild-dir := $(if $(filter /%,$(src)),$(src),$(srctree)/$(src)) |

所以 kbuild-dir = ./scripts/basic

4.1.4.3 kbuild-file的定义

在scripts/Makefile.build有如下定义

|  | kbuild-file := $(if $(wildcard $(kbuild-dir)/Kbuild),$(kbuild-dir)/Kbuild,$(kbuild-dir)/Makefile) |

所以kbuild-file = ./scripts/basic/Makefile

所以include $(kbuild-file)即为include ./scripts/basic/Makefile

在./scripts/basic/Makefile中：

|  | # note：scripts/basic/Makefile |
|  | hostprogs-y := fixdep |
|  | always := $(hostprogs-y) |
|  |  |
|  | # fixdep is needed to compile other host programs |
|  | $(addprefix $(obj)/,$(filter-out fixdep,$(always))): $(obj)/fixdep |

所以always = fixdep

4.1.4.4 又在Makefile.build中包含include scripts/Makefile.lib

而在scripts/Makefile.lib中

|  | # note：scripts/Makefile.lib |
|  | always := $(addprefix $(obj)/,$(always)) |

所以最终 always = scripts/basic/fixdep 。

故__build 展开如下：
__build: scripts/basic/fixdep
@:

1. 在Makefile.build中有如下定义：

|  | # note：scripts/Makefile.build |
|  | ifneq ($(hostprogs-y)$(hostprogs-m),) |
|  |  include scripts/Makefile.host |
|  | endif  |

在./scripts/basic/Makefile中hostprogs-y = fixdep, 所以scripts/Makefile.host被包含进Makefile.build; 在scripts/Makefile.host中

|  | # note：scripts/Makefile.host |
|  | \_\_hostprogs := $(sort $(hostprogs-y) $(hostprogs-m)) |

hostprogs-m为空，所以__hostprogs = fixdep。 在scripts/Makefile.host中

|  | # note：scripts/Makefile.host |
|  | # C code |
|  | # Executables compiled from a single .c file |
|  | host-csingle := $(foreach m,$(\_\_hostprogs), \ |
|  |  $(if $($(m)-objs)$($(m)-cxxobjs)$($(m)-sharedobjs),,$(m))) |
|  | ...... |
|  | host-csingle := $(addprefix $(obj)/,$(host-csingle))  |

因为fixdep-objs与fixdep-cxxobjs都不存在，所以host-csingle = fixdep； 又 host-csingle := $ (addprefix $ (obj)/,$(host-csingle))，所以host-csingle = scripts/basic/fixdep。 host-csingle规则如下：

|  | # note：scripts/Makefile.host |
|  | $(host-csingle): $(obj)/%: $(src)/%.c FORCE |
|  |  $(call if\_changed\_dep,host-csingle)  |

等价于：

|  | scripts/basic/fixdep:scripts/basic/fixdep.c FORCE |
|  |  $(call if\_changed\_dep,host-csingle)  |

2. if_changed_dep在scripts/Kbuild.include中定义

|  | # note：scripts/Kbuild.include |
|  | # Execute the command and also postprocess generated .d dependencies file. |
|  | if\_changed\_dep = $(if $(strip $(any-prereq) $(arg-check) ), \ |
|  |  @set -e; \ |
|  |  $(echo-cmd) $(cmd\_$(1)); \ |
|  |  scripts/basic/fixdep $(depfile) $@ '$(make-cmd)' > $(dot-target).tmp;\ |
|  |  rm -f $(depfile); \ |
|  |  mv -f $(dot-target).tmp $(dot-target).cmd) |

2.1 $(strip $(any-prereq) $(arg-check) ) (1) any-prereq在scripts/Kbuild.include中定义

|  | # note：scripts/Kbuild.include |
|  |  any-prereq = $(filter-out $(PHONY),$?) $(filter-out $(PHONY) $(wildcard $^),$^) |

$ ? 表示所有比目标还要新的依赖文件;$ ^ 表示所有的依赖文件，$(filter-out $ (PHONY), $?)就是过滤到比目标还要新的依赖文件中的伪目标，即为 scripts/basic/fixdep.c， $ (filter-out $ (PHONY) $ (wildcard $ ^ ), $^)表示过滤掉所有的依赖文件中的伪目标与存在的依赖文件，这里为空，所以any-prereq = scripts/basic/fixdep.c。 (2) arg-check在scripts/Kbuild.include中定义：

|  | # note：scripts/Kbuild.include |
|  | ifneq ($(KBUILD\_NOCMDDEP),1) |
|  |  arg-check = $(strip $(filter-out $(cmd\_$(1)), $(cmd\_$@)) \ |
|  |  $(filter-out $(cmd\_$@), $(cmd\_$(1))) ) |
|  | else |
|  |  arg-check = $(if $(strip $(cmd\_$@)),,1) |
|  | endif |

KBUILD_NOCMDDEP是在make命令行中定义，我们并没有定义，所以：

|  | arg-check = $(strip $(filter-out $(cmd\_$(1)), $(cmd\_$@)) $(filter-out $(cmd\_$@), $(cmd\_$(1))) ) |

<1> $ (filter-out $ (cmd_ $ (1)), $ (cmd_ $@)) 表示过滤掉 $(cmd_ $@)中符合 $(cmd_ $(1))的项。 $(1)表示if_changed_dep函数的第一个参数host-csingle， $@表示目标文件scripts/basic/fixdep。 <2> cmd_scripts/basic/fixdep并没有定义，所以 $(filter-out $(cmd_ $(1)), $(cmd_ $@))为空； <3> cmd_host-csingle 在Makefile.host中定义：

|  | cmd\_host-csingle = $(HOSTCC) $(hostc\_flags) -o $@ $< $(HOST\_LOADLIBES) $(HOSTLOADLIBES\_$(@F)) |

所以arg-check = $ (filter-out $ (cmd_$ @), $ (cmd_$ (1))) = $ (HOSTCC) $ (hostc_flags) -o $@ $< $(HOST_LOADLIBES) $(HOSTLOADLIBES_ $(@F))

$(any-prereq) $(arg-check)都为非空，所以：

|  | if\_changed\_dep = @set -e; \ /如果任何语句的执行结果不是true则应该退出 |
|  |  $(echo-cmd) $(cmd\_$(1)); \ |
|  |  scripts/basic/fixdep $(depfile) $@ '$(make-cmd)' > $(dot-target).tmp;\ |
|  |  rm -f $(depfile); \ |
|  |  mv -f $(dot-target).tmp $(dot-target).cmd) |

2.2 $(echo-cmd) $(cmd_ $ (1))等价于$(echo-cmd) $(cmd_host-csingle)

|  | echo-cmd = $(if $( $(quiet)cmd\_$(1)),echo ' $(call escsq, $( $(quiet)cmd\_ $(1))) $(echo-why)';） |

quiet=quiet_，在顶层Makefile分析过(当然如果你想看到更详细的打印，您可以通过传入V值，来改变)， $(cmd_host-csingle)上面分析过，存在，所以：

|  | echo-cmd = echo ' $(call escsq,$(cmd\_host-csingle))$(echo-why)'; |

在scripts/Kbuild.include中：

|  | # Escape single quote for use in echo statements |
|  | escsq = $(subst $(squote),'\$(squote)',$1) |
|  | ifeq ($(KBUILD\_VERBOSE),2) |
|  | why = \ |
|  |  $(if $(filter $@, $(PHONY)),- due to target is PHONY, \ |
|  |  $(if $(wildcard $@), \ |
|  |  $(if $(strip $(any-prereq)),- due to: $(any-prereq), \ |
|  |  $(if $(arg-check), \ |
|  |  $(if $(cmd\_$@),- due to command line change, \ |
|  |  $(if $(filter $@, $(targets)), \ |
|  |  - due to missing .cmd file, \ |
|  |  - due to $(notdir $@) not in $$(targets) \ |
|  |  ) \ |
|  |  ) \ |
|  |  ) \ |
|  |  ), \ |
|  |  - due to target missing \ |
|  |  ) \ |
|  |  ) |
|  |  |
|  | echo-why = $(call escsq, $(strip $(why))) |
|  | endif |

KBUILD_VERBOSE一般我们会采用默认值0(需要调试编译除外)，所以 echo-why 为空。

|  | quiet\_cmd\_host-csingle = HOSTCC $@ //用来打印 |
|  | cmd\_host-csingle = '$(HOSTCC) $(hostc\_flags) -o $@ $< $(HOST\_LOADLIBES) $(HOSTLOADLIBES\_$(@F))' |

$(HOSTCC)为cc，此处不再深入解释，hostc_flags在Makefile.host中定义：

|  | ##### |
|  | # Handle options to gcc. Support building with separate output directory |
|  |  |
|  | \_hostc\_flags = $(HOSTCFLAGS) $(HOST\_EXTRACFLAGS) \ |
|  |  $(HOSTCFLAGS\_$(basetarget).o) //-Wall -Wstrict-prototypes -O2 -fomit-frame-pointer  |
|  | \_hostcxx\_flags = $(HOSTCXXFLAGS) $(HOST\_EXTRACXXFLAGS) \ |
|  |  $(HOSTCXXFLAGS\_$(basetarget).o) |
|  | ifeq ($(KBUILD\_SRC),) //KBUILD\_SRC在make命令行定义，此处未定义 |
|  | \_\_hostc\_flags = $(\_hostc\_flags) |
|  | \_\_hostcxx\_flags = $(\_hostcxx\_flags) |
|  | else |
|  | \_\_hostc\_flags = -I$(obj) $(call flags,\_hostc\_flags) |
|  | \_\_hostcxx\_flags = -I$(obj) $(call flags,\_hostcxx\_flags) |
|  | endif |
|  | hostc\_flags = -Wp,-MD,$(depfile) $(\_\_hostc\_flags)  |

在scripts/Kbuild.include中：

|  | comma := , |
|  | dot-target = $(dir $@).$(notdir $@) //scripts/basic/.fixdep |
|  | depfile = $(subst $(comma),\_,$(dot-target).d) //scripts/basic/.fixdep.d |
|  | hostc\_flags = -Wp,-MD,scripts/basic/.fixdep.d -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer |
|  |  |

综上 cmd_host-csingle = cc -Wp,-MD,scripts/basic/.fixdep.d -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer -o scripts/basic/fixdep scripts/basic/fixdep.c

所以echo-cmd 的作用是打印quiet_cmd_host-csingle（HOSTCC $ @ ）或者cmd_host-csingle（根据顶层MakefileV值决定），$ (cmd_$(1))即为执行cmd_host-csingle生成fixdep同时生成fixdep的依赖文件.fixdep.d

（2.3） scripts/basic/fixdep $(depfile) $@ ’ $(make-cmd)’ > $(dot-target).tmp 等价于：scripts/basic/fixdep scripts/basic/.fixdep.d scripts/basic/fixdep ‘cc -Wp,-MD,scripts/basic/.fixdep.d -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer -o scripts/basic/fixdep scripts/basic/fixdep.c’ > scripts/basic/.fixdep.tmp

（2.4） rm -f $(depfile) 删除scripts/basic/.fixdep.d

（2.5） mv -f $(dot-target).tmp $(dot-target).cmd) 将scripts/basic/.fixdep.tmp重命名为scripts/basic/.fixdep.cmd

总结：生成scripts/basic/fixdep的过程中会先打印cc -Wp,-MD,scripts/basic/.fixdep.d -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer -o scripts/basic/fixdep scripts/basic/fixdep.c同时执行该语句生成fixdep，再用fixdep生成.fixdep.cmd

4.2 依赖 outputmakefile

|  | # 顶层Makefile |
|  | # outputmakefile generates a Makefile in the output directory, if using a |
|  | # separate output directory. This allows convenient use of make in the |
|  | # output directory. |
|  | outputmakefile: |
|  | ifneq ($(KBUILD\_SRC),) |
|  |  $(Q)ln -fsn $(srctree) source |
|  |  $(Q)$(CONFIG\_SHELL) $(srctree)/scripts/mkmakefile \ |
|  |  $(srctree) $(objtree) $(VERSION) $(PATCHLEVEL) |
|  | endif |

上面批注已经说的很清楚了，outputmakefile 在输出目录中生成一个 Makefile，如果使用单独的输出目录。 这允许在输出目录中方便地使用 make。当KBUILD_SRC不为空时，才会编译到这里。

4.3 依赖 FORCE

|  | # 顶层Makefile |
|  | PHONY += FORCE |
|  | FORCE: |

实际上它是一个伪目标，从上面看到，FORCE 既没有依赖的规则，其底下也没有可执行的命令。如果一个规则没有命令或者依赖，而且它的目标不是一个存在的文件名，在执行此规则时，目标总会被认为是最新的。也就是说，这个规则一旦被执行，make 就认为它所表示的目标已经被更新过。当将这样的目标(FORCE)作为一个规则的依赖时(如上)，由于依赖总被认为是被更新过的，所以作为依赖所在的规则定义的命令总会被执行。

4.4 规则 $ (Q)$(MAKE) $(build)=scripts/kconfig $@

等价于：make -f $(srctree)/scripts/Makefile.build obj=scripts/kconfig myimx8mmek240-8mm-2g_defconfig

在scripts/kconfig/Makefile中(至于为什么会引用scripts/kconfig/Makefile，参见4.1小节)

|  | # note：scripts/kconfig/Makefile |
|  | ifdef KBUILD\_KCONFIG |
|  | Kconfig := $(KBUILD\_KCONFIG) |
|  | else |
|  | Kconfig := Kconfig |
|  | endif |
|  |  |
|  | %\_defconfig: $(obj)/conf |
|  |  $(Q)$< $(silent) --defconfig=arch/$(SRCARCH)/configs/$@ $(Kconfig) //$< = $(obj)/conf |
|  |  |
|  | # Added for U-Boot (backward compatibility) |
|  | %\_config: %\_defconfig |
|  |  @: |

编译的流程为： （1）先编译scripts/kconfig/conf可执行文件； （2）再执行scripts/kconfig/conf --defconfig=arch/…/configs/myimx8mmek240-8mm-2g_defconfig Kconfig语句

编译打印如下

|  | make -f ./scripts/Makefile.build obj=scripts/kconfig myimx8mmek240-8mm-2g\_defconfig |
|  |  cc -Wp,-MD,scripts/kconfig/.conf.o.d -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer -I/usr/include/ncursesw -DCURSES\_LOC="" -DNCURSES\_WIDECHAR=1 -DLOCALE -c -o scripts/kconfig/conf.o scripts/kconfig/conf.c |
|  |  cat scripts/kconfig/zconf.tab.c\_shipped > scripts/kconfig/zconf.tab.c |
|  |  cat scripts/kconfig/zconf.lex.c\_shipped > scripts/kconfig/zconf.lex.c |
|  |  cat scripts/kconfig/zconf.hash.c\_shipped > scripts/kconfig/zconf.hash.c |
|  |  cc -Wp,-MD,scripts/kconfig/.zconf.tab.o.d -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer -I/usr/include/ncursesw -DCURSES\_LOC="" -DNCURSES\_WIDECHAR=1 -DLOCALE -Iscripts/kconfig -c -o scripts/kconfig/zconf.tab.o scripts/kconfig/zconf.tab.c |
|  |  cc -o scripts/kconfig/conf scripts/kconfig/conf.o scripts/kconfig/zconf.tab.o |
|  | scripts/kconfig/conf --defconfig=arch/../configs/myimx8mmek240-8mm-2g\_defconfig Kconfig |
|  | # |
|  | # configuration written to .config |
|  | # |

5 总结

经过前面的分析可知：当执行make xxx_deconfig时，最终会执行以下两个语句： （1）make -f $(srctree)/scripts/Makefile.build obj=scripts/basic （2）make -f ./scripts/Makefile.build obj=scripts/kconfig xxx_deconfig