u-boot-2016.09 make工具之fixdep

u-boot-2016.09 make工具之fixdep

1. 概述

fixdep工具的源码位于scripts/basic/fixdep.c，代码本身并不复杂。但作用是什么？哪里调用，如何调用，输入和输出是什么？咋一看却不甚清楚。 
本文废话太多，如果只想看结论，请直接跳转到文末查看“TL;DR”一节。

2. 哪里调用？

到底哪里调用了fixdep？

2.1 直接搜索fixdep

不妨在u-boot代码里搜索下：

ygu@ubuntu:/opt/work/u-boot/u-boot-2016.09$ grep -rnw fixdep . --exclude-dir=basic
./scripts/Kbuild.include:230:# if_changed_dep  - as if_changed, but uses fixdep to reveal dependencies
./scripts/Kbuild.include:266:   scripts/basic/fixdep $(depfile) $@ '$(make-cmd)' > $(dot-target).tmp;\
./scripts/Makefile.build:272:   scripts/basic/fixdep $(depfile) $@ '$(call make-cmd,cc_o_c)' >    \
./board/bosch/shc/README:30:  HOSTCC  scripts/basic/fixdep
 
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grep参数说明:
-r，递归搜索目录
-n，显示匹配结果的行号
-w，按单词搜索
--exclude-dir=basic，忽略basic子目录，此目录是fixdep.c自身的代码目录

总共有4条匹配结果，只有在scripts/Kbuild.include的266行和scripts/Makefile.build的272行有调用，其余都跟fixdep调用无关。

2.1.1 if_changed_dep调用fixdep

scripts/Kbuild.include中的匹配结果是自定义函数if_changed_dep调用了fixdep：

# 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)
 
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进一步搜索对if_changed_dep的调用：

ygu@ubuntu:/opt/work/u-boot/u-boot-2016.09$ grep -rnw if_changed_dep .
./scripts/Makefile.spl:299:     $(call if_changed_dep,cpp_lds)
./scripts/Makefile.lib:299:     $(call if_changed_dep,dtc)
./scripts/Kbuild.include:229:# if_changed_dep  - as if_changed, but uses fixdep to reveal dependencies
./scripts/Kbuild.include:263:if_changed_dep = $(if $(strip $(any-prereq) $(arg-check) ),                  \
./scripts/Makefile.build:175:   $(call if_changed_dep,cc_s_c)
./scripts/Makefile.build:181:   $(call if_changed_dep,cc_i_c)
./scripts/Makefile.build:296:   $(call if_changed_dep,cc_lst_c)
./scripts/Makefile.build:310:   $(call if_changed_dep,as_s_S)
./scripts/Makefile.build:316:   $(call if_changed_dep,as_o_S)
./scripts/Makefile.build:328:   $(call if_changed_dep,cpp_lds_S)
./scripts/Makefile.host:99:     $(call if_changed_dep,host-csingle)
./scripts/Makefile.host:116:    $(call if_changed_dep,host-cobjs)
./scripts/Makefile.host:133:    $(call if_changed_dep,host-cxxobjs)
./Kbuild:44:    $(call if_changed_dep,cc_s_c)
./Kbuild:65:    $(call if_changed_dep,cc_s_c)
./arch/arm/imx-common/Makefile:48:      $(call if_changed_dep,cpp_cfg)
./arch/sandbox/cpu/Makefile:22: $(call if_changed_dep,cc_os.o)
./arch/sandbox/cpu/Makefile:24: $(call if_changed_dep,cc_os.o)
./arch/sandbox/cpu/Makefile:33: $(call if_changed_dep,cc_eth-raw-os.o)
./examples/api/Makefile:64:     $(call if_changed_dep,as_o_S)
./Makefile:1118:        $(call if_changed_dep,cpp_lds)
./Makefile:1328:        $(call if_changed_dep,cpp_lds)
 
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检查以上所有对if_changed_dep调用的地方，都有一个共同点。那就是新生成一个目标时，调用if_changed_dep去生成它的依赖文件。

例如，

• scripts/Makefile.lib中将%.dts编译输出为%.dtb：

$(obj)/%.dtb: $(src)/%.dts FORCE
    $(call if_changed_dep,dtc)
 
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• scripts/Makefile.build中将%.S编译输出为%.o：

$(obj)/%.o: $(src)/%.S FORCE
    $(call if_changed_dep,as_o_S)
 
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• scripts/Makefile.host中将%.c编译输出为可执行文件%：`

$(host-csingle): $(obj)/%: $(src)/%.c FORCE
    $(call if_changed_dep,host-csingle)
 
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以上所有对if_changed_dep调用的地方，还有另外一个共同点，if_changed_dep的调用也还有另外一个特别的地方，就是除了Makefile.host中调用if-_changed_dep，是将%.c编译输出为%.o外，还没有其它的调用是用于编译%.c文件的。

Makefile.host在Kbuild体系中，用于编译在在主机上运行的程序，而不是编译u-boot自身的文件。

2.1.2 rule_cc_o_c调用fixdep

scripts/Makefile.build中的匹配结果是自定义宏rule_cc_o_c调用了fixdep：

define rule_cc_o_c
    $(call echo-cmd,checksrc) $(cmd_checksrc)              \
    $(call echo-cmd,cc_o_c) $(cmd_cc_o_c);               \
    $(cmd_modversions)                       \
    $(call echo-cmd,record_mcount)                   \
    $(cmd_record_mcount)                         \
    scripts/basic/fixdep $(depfile) $@ '$(call make-cmd,cc_o_c)' >    \
                                                  $(dot-target).tmp;  \
    rm -f $(depfile);                        \
    mv -f $(dot-target).tmp $(dot-target).cmd
endef
 
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进一步搜索对rule_cc_o_c的调用：

ygu@ubuntu:/opt/work/u-boot/u-boot-2016.09$ grep -rnw rule_cc_o_c .               
./scripts/Makefile.build:201:# (See cmd_cc_o_c + relevant part of rule_cc_o_c)
./scripts/Makefile.build:266:define rule_cc_o_c
 
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结果显示除了定义之外，并没有显示rule_cc_o_c被引用。那换一种方式，搜索cc_o_c：

ygu@ubuntu:/opt/work/u-boot/u-boot-2016.09$ grep -rnw cc_o_c .     
./scripts/Makefile.build:268:   $(call echo-cmd,cc_o_c) $(cmd_cc_o_c);                            \
./scripts/Makefile.build:272:   scripts/basic/fixdep $(depfile) $@ '$(call make-cmd,cc_o_c)' >    \
./scripts/Makefile.build:281:   $(call if_changed_rule,cc_o_c)
./scripts/Makefile.build:287:   $(call if_changed_rule,cc_o_c)
./examples/api/Makefile:60:     $(call if_changed_rule,cc_o_c)
 
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得到5项搜索结果，其前两行实际上是宏rule_cc_o_c定义本身，最后一行是u-boot例子里面的调用，也可以忽略。 
重点是scripts/Makefile.build的中间两项：

# Built-in and composite module parts
$(obj)/%.o: $(src)/%.c $(recordmcount_source) FORCE
    $(call cmd,force_checksrc)
    $(call if_changed_rule,cc_o_c)

# Single-part modules are special since we need to mark them in $(MODVERDIR)

$(single-used-m): $(obj)/%.o: $(src)/%.c $(recordmcount_source) FORCE
    $(call cmd,force_checksrc)
    $(call if_changed_rule,cc_o_c)
    @{ echo $(@:.o=.ko); echo $@; } > $(MODVERDIR)/$(@F:.o=.mod)
 
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很显然，$(simple-used-m)规则从字面上看是用于生成.ko文件的，而u-boot并不生成模块文件，所以实际上用于编译%.c生成%.o的是前一个规则。

2.1.3 fixdep调用结论

从前两节的分析看，以下情况会调用fixdep进行处理：

• 新生成一个目标时，调用if_changed_dep检测并更新依赖文件，其中if_changed_dep会调用fixdep去处理依赖文件，但是将用于生成u-boot的%.c文件编译为%.o规则除外
• 将生成u-boot的%.c编译为%.o时会调用rule_cc_o_c，rule_cc_o_c中又会调用fixdep生成%.o的依赖文件.%.cmd

3. 如何调用？

通过fixdep.c的usage()函数，我们可以看到fixdep的用法：

fixdep <depfile> <target> <cmdline>
 
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fixdep接收三个参数，分别是：

• <depfile>：编译产生的依赖文件*.d
• <target>：编译生成的目标
• <cmdline>：编译使用的命令

4. 输入和输出

看一看调用if_changed_dep的实例： 
修改if_changed_dep中，显示调用fixdep的命令，并保留原有的依赖文件:

if_changed_dep = $(if $(strip $(any-prereq) $(arg-check) ),                  \
    @set -e;                                                             \
    $(echo-cmd) $(cmd_$(1));                                             \
    echo 'call fixdep: scripts/basic/fixdep $(depfile) $@ "$(make-cmd)"';\
    scripts/basic/fixdep $(depfile) $@ '$(make-cmd)' > $(dot-target).tmp;\
    mv -f $(dot-target).tmp $(dot-target).cmd)
 
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重新执行make rpi_3_32b_defconfig，得到如下log:

ygu@fs-ygu:/opt/work/u-boot/u-boot-2016.09$ make rpi_3_32b_defconfig
  HOSTCC  scripts/basic/fixdep
call fixdep: 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  "
  HOSTCC  scripts/kconfig/conf.o
call fixdep: scripts/basic/fixdep scripts/kconfig/.conf.o.d scripts/kconfig/conf.o "cc -Wp,-MD,scripts/kconfig/.conf.o.d -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer    -I/usr/include/ncursesw   -DCURSES_LOC="<ncurses.h>" -DLOCALE   -c -o scripts/kconfig/conf.o scripts/kconfig/conf.c"
  SHIPPED scripts/kconfig/zconf.tab.c
  SHIPPED scripts/kconfig/zconf.lex.c
  SHIPPED scripts/kconfig/zconf.hash.c
  HOSTCC  scripts/kconfig/zconf.tab.o
call fixdep: scripts/basic/fixdep scripts/kconfig/.zconf.tab.o.d scripts/kconfig/zconf.tab.o "cc -Wp,-MD,scripts/kconfig/.zconf.tab.o.d -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer    -I/usr/include/ncursesw   -DCURSES_LOC="<ncurses.h>" -DLOCALE  -Iscripts/kconfig -c -o scripts/kconfig/zconf.tab.o scripts/kconfig/zconf.tab.c"
  HOSTLD  scripts/kconfig/conf
#
# configuration written to .config
#
 
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从log可以看到，执行make rpi_3_32b_defconfig一共调用了3次fixdep，以处理scripts/basic/.fixdep.d为例，调用的命令的参数分别为：

• depfile = scripts/basic/.fixdep.d
• target = scripts/basic/fixdep
• cmdline = "cc -Wp,-MD,scripts/basic/.fixdep.d -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer -o scripts/basic/fixdep scripts/basic/fixdep.c "

4.1 输入和输出

编译过程中生成的依赖文件.fixdep.d作为输入，经过处理得到.fixdep.cmd文件，对比其中的变化：

原来的.fixdep.d:

fixdep.o: scripts/basic/fixdep.c /usr/include/stdc-predef.h \
 ... \ /* 省略中间的若干头文件 */
 /usr/include/x86_64-linux-gnu/bits/in.h
 
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新生成的.fixdep.cmd：

cmd_scripts/basic/fixdep := "cc -Wp,-MD,...scripts/basic/fixdep.c"

source_scripts/basic/fixdep := scripts/basic/fixdep.c

deps_scripts/basic/fixdep := xxx.h \
    $(wildcard include/config/his/driver.h) \
    $(wildcard include/config/my/option.h) \
    $(wildcard include/config/.h) \
    $(wildcard include/config/foo.h) \
    $(wildcard include/config/boom.h) \
    $(wildcard include/config/is/.h) \
  /usr/include/stdc-predef.h \
  ... \ /* 省略中间的若干头文件，同.fixdep.d */
  /usr/include/x86_64-linux-gnu/bits/in.h \

scripts/basic/fixdep: $(deps_scripts/basic/fixdep)

$(deps_scripts/basic/fixdep):
 
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新的.fixdep.cmd中增加了跟目标相关的变量cmd_xxx，source_xxx，deps_xxx和目标xxx对deps_xxx的依赖规则。

fixdep.c的代码操作比较简单，这里略去对代码的分析。

>

**有个疑问，没搞懂dep_xxx开始部分匹配wildcard包含的头文件到底是如何来的？ 
很明显，这部分是由use_config()函数生成的，具体如何生成，大神们的请来指点下。**

4.2 .*.cmd的引用

顶层Makefile是这样引用.*.cmd文件的：

# read all saved command lines

targets := $(wildcard $(sort $(targets)))
cmd_files := $(wildcard .*.cmd $(foreach f,$(targets),$(dir $(f)).$(notdir $(f)).cmd))

ifneq ($(cmd_files),)
  $(cmd_files): ;  # Do not try to update included dependency files
  include $(cmd_files)
endif
 
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根据待生成的目标targets生成cmd_files列表，然后用include指令包含所有这些.*.cmd文件。 
以生成的arm/cpu/armv7/.start.o.cmd为例，文件中包含：

cmd_arch/arm/cpu/armv7/start.o := arm-linux-gnueabi-gcc ... -c -o arch/arm/cpu/armv7/start.o arch/arm/cpu/armv7/start.S

source_arch/arm/cpu/armv7/start.o := arch/arm/cpu/armv7/start.S

deps_arch/arm/cpu/armv7/start.o := \
    $(wildcard include/config/omap44xx.h) \
    $(wildcard include/config/spl/build.h) \
    ...

arch/arm/cpu/armv7/start.o: $(deps_arch/arm/cpu/armv7/start.o)

$(deps_arch/arm/cpu/armv7/start.o):
 
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实际上只用到了依赖规则：

deps_arch/arm/cpu/armv7/start.o := \
    $(wildcard include/config/omap44xx.h) \
    $(wildcard include/config/spl/build.h) \
    ...

arch/arm/cpu/armv7/start.o: $(deps_arch/arm/cpu/armv7/start.o)

$(deps_arch/arm/cpu/armv7/start.o):
 
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对于cmd_arch/arm/cpu/armv7/start.o和source_arch/arm/cpu/armv7/start.o，u-boot编译时并没有用到。

至于cmd_xxx和source_xxx，我能够想到的用处就是存放一些编译用到的信息，例如cmd_xxx表示生成所用的命令，source_xxx表示生成目标的source code，如果想看某一个文件时如何生成的，去检查.*.cmd文件就行了。其实这也是蛮有用的。

例如，我想看看文件u-boot.bin是如何生成的，那就去检查.u-boot.bin.cmd，一目了然了：

cmd_u-boot.bin := cp u-boot-nodtb.bin u-boot.bin
 
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我去，编译生成的u-boot.bin竟然是u-boot-nodtb.bin通过cp来的~~哈哈。

5. TL;DR

上面部分主要表述整个分析的过程，废话太多。以下简略说明重点。

编译时，编译器会根据选项-MD自动生成依赖文件*.d，用fixdep更新*.d文件生成新的依赖文件.*.cmd。

fixdep被两个地方调用：

• rule_cc_o_c：编译u-boot自身的*.c文件时，rule_cc_o_c调用fixdep去更新生成%.c的依赖文件.%.cmd

• if_changed_dep：适用于除了上述的rule_cc_o_c外的其它目标依赖文件的生成，例如生成主机上执行的程序，处理dts文件等，也包括汇编文件生成*.o，生成*.s，*.lst等。

通过查看fixdep输出的.*.cmd文件可以知道对应的目标文件*是如何生成的。