Linux内核---10.obj-y中将.c编译为.o流程
2016-07-02 14:37
549 查看
先去编译obj-y,以init下的obj-y为例:
obj-y=init/main.o init/version.o init/mounts.o init/noinitramfs.o init/calibrate.o
首先找到将.c编译为.o的规则:
点击(此处)折叠或打开
linux-2.6.30.4/scripts/Makefile.build
226 # Built-in and composite module parts
227 $(obj)/%.o: $(src)/%.c
FORCE
228
$(call cmd,force_checksrc)
229
$(call if_changed_rule,cc_o_c)
将.c编译为.o要分两步
1. L228,如果KBUILD_CHECKSRC为空,不做任何操作;不为空,没看。
2. L229,编译的具体操作。
1.1 检查 L228 $(call cmd,force_checksrc)
点击(此处)折叠或打开
linux-2.6.30.4/scripts/Kbuild.include
154 # echo command.
155 # Short version is used, if $(quiet) equals
`quiet_', otherwise full one.
156 echo-cmd = $(if $($(quiet)cmd_$(1)),\
157 echo ' $(call escsq,$($(quiet)cmd_$(1)))$(echo-why)';)
158
159 # printing commands
160 cmd = @$(echo-cmd) $(cmd_$(1))
cmd 定义在L160处,如果cmd_force_checksrc不为空,则把cmd_force_checksrc这个命令打印出来,然后执行cmd_force_checksrc
转到cmd_force_checksrc定义处:
linux-2.6.30.4/scripts/Makefile.build
98 # Linus' kernel sanity checking tool
99 ifneq ($(KBUILD_CHECKSRC),0)
100 ifeq ($(KBUILD_CHECKSRC),2)
101 quiet_cmd_force_checksrc = CHECK $<
102 cmd_force_checksrc = $(CHECK) $(CHECKFLAGS) $(c_flags) $< ;
103 else
104 quiet_cmd_checksrc = CHECK $<
105 cmd_checksrc = $(CHECK) $(CHECKFLAGS) $(c_flags) $< ;
106 endif
107 endif
由于此时 KBUILD_CHECKSRC=0,所以cmd_force_checksrc为空,L156处的if条件为false,echo不执行,L160处cmd_force_checksrc为空,也不执行。
2. 下面开始执行L229 $(call if_changed_rule,cc_o_c),首先转到定义处:
点击(此处)折叠或打开
linux-2.6.30.4/scripts/Kbuild.include
208 if_changed_rule = $(if $(strip
$(any-prereq) $(arg-check) ), \
209 @set -e; \
210 $(rule_$(1)))
$(strip $(any-prereq) $(arg-check),如果目标有更新则调用:rule_cc_o_c
linux-2.6.30.4/scripts/Makefile.build
215 define rule_cc_o_c
216 $(call echo-cmd,checksrc) $(cmd_checksrc) \
217 $(call echo-cmd,cc_o_c) $(cmd_cc_o_c); \
218 $(cmd_modversions) \
219 $(cmd_record_mcount) \
220 scripts/basic/fixdep $(depfile) $@ '$(call make-cmd,cc_o_c)' > \
221 $(dot-target).tmp; \
222 rm -f $(depfile); \
223 mv -f $(dot-target).tmp
$(dot-target).cmd
224 endef
rule_cc_o_c
2.1 echo-cmd
&& cmd_checksrc :不执行
2.2 echo-cmd &&
cmd_cc_o_c :打印cmd_cc_o_c的内容,并执行cmd_cc_o_c将.c编译为.o
2.3 cmd_modversions :不执行
2.4 cmd_record_mcount :不执行
2.5 生成命令.cmd
下面逐条分析:
2.1-2.2 echo-cmd
&& cmd_checksrc 和 echo-cmd &&
cmd_cc_o_c
点击(此处)折叠或打开
linux-2.6.30.4/scripts/Kbuild.include
154 # echo command.
155 # Short version is used, if $(quiet) equals
`quiet_', otherwise full one.
156 echo-cmd = $(if $($(quiet)cmd_$(1)),\
157 echo ' $(call escsq,$($(quiet)cmd_$(1)))$(echo-why)';)
cmd_checksrc为空,不执行
linux-2.6.30.4/scripts/Makefile.build
178 ifndef CONFIG_MODVERSIONS
179 cmd_cc_o_c = $(CC) $(c_flags) -c -o $@ $<
$(call echo-cmd,cc_o_c)将执行的编译命令打印出来, $(cmd_cc_o_c)执行具体的编译命令。这将会在命令行中看到一坨坨的打印。
2.3 cmd_modversions
点击(此处)折叠或打开
linux-2.6.30.4/scripts/Makefile.build
178 ifndef CONFIG_MODVERSIONS
179 cmd_cc_o_c = $(CC) $(c_flags) -c -o $@ $<
180
181 else
194 cmd_cc_o_c = $(CC) $(c_flags) -c -o $(@D)/.tmp_$(@F) $<
195 cmd_modversions = ...
因为此处没有定义 CONFIG_MODVERSIONS, 所以cmd_modversions为空。
2.4 cmd_record_mcount
点击(此处)折叠或打开
208 ifdef CONFIG_FTRACE_MCOUNT_RECORD
209 cmd_record_mcount = perl $(srctree)/scripts/recordmcount.pl "$(ARCH)" \
210 "$(if $(CONFIG_64BIT),64,32)" \
211 "$(OBJDUMP)" "$(OBJCOPY)" "$(CC)" "$(LD)" "$(NM)" "$(RM)" "$(MV)" \
212 "$(if $(part-of-module),1,0)" "$(@)";
213 endif
CONFIG_FTRACE_MCOUNT_RECORD 没有定义,所以为空
总结一下:
虽然写了这么多,但是有用处的只有两个echo-cmd &&
cmd_cc_o_c和 mv ,打印cmd_cc_o_c的内容,并执行cmd_cc_o_c将.c编译为.o,把命令保存到.cmd文件中。假设让我自己写出来的Makefile可能也就是$(CC)
$(c_flags) -c -o $@ $<这么一句。
obj-y=init/main.o init/version.o init/mounts.o init/noinitramfs.o init/calibrate.o
首先找到将.c编译为.o的规则:
点击(此处)折叠或打开
linux-2.6.30.4/scripts/Makefile.build
226 # Built-in and composite module parts
227 $(obj)/%.o: $(src)/%.c
FORCE
228
$(call cmd,force_checksrc)
229
$(call if_changed_rule,cc_o_c)
将.c编译为.o要分两步
1. L228,如果KBUILD_CHECKSRC为空,不做任何操作;不为空,没看。
2. L229,编译的具体操作。
1.1 检查 L228 $(call cmd,force_checksrc)
点击(此处)折叠或打开
linux-2.6.30.4/scripts/Kbuild.include
154 # echo command.
155 # Short version is used, if $(quiet) equals
`quiet_', otherwise full one.
156 echo-cmd = $(if $($(quiet)cmd_$(1)),\
157 echo ' $(call escsq,$($(quiet)cmd_$(1)))$(echo-why)';)
158
159 # printing commands
160 cmd = @$(echo-cmd) $(cmd_$(1))
cmd 定义在L160处,如果cmd_force_checksrc不为空,则把cmd_force_checksrc这个命令打印出来,然后执行cmd_force_checksrc
转到cmd_force_checksrc定义处:
linux-2.6.30.4/scripts/Makefile.build
98 # Linus' kernel sanity checking tool
99 ifneq ($(KBUILD_CHECKSRC),0)
100 ifeq ($(KBUILD_CHECKSRC),2)
101 quiet_cmd_force_checksrc = CHECK $<
102 cmd_force_checksrc = $(CHECK) $(CHECKFLAGS) $(c_flags) $< ;
103 else
104 quiet_cmd_checksrc = CHECK $<
105 cmd_checksrc = $(CHECK) $(CHECKFLAGS) $(c_flags) $< ;
106 endif
107 endif
由于此时 KBUILD_CHECKSRC=0,所以cmd_force_checksrc为空,L156处的if条件为false,echo不执行,L160处cmd_force_checksrc为空,也不执行。
2. 下面开始执行L229 $(call if_changed_rule,cc_o_c),首先转到定义处:
点击(此处)折叠或打开
linux-2.6.30.4/scripts/Kbuild.include
208 if_changed_rule = $(if $(strip
$(any-prereq) $(arg-check) ), \
209 @set -e; \
210 $(rule_$(1)))
$(strip $(any-prereq) $(arg-check),如果目标有更新则调用:rule_cc_o_c
linux-2.6.30.4/scripts/Makefile.build
215 define rule_cc_o_c
216 $(call echo-cmd,checksrc) $(cmd_checksrc) \
217 $(call echo-cmd,cc_o_c) $(cmd_cc_o_c); \
218 $(cmd_modversions) \
219 $(cmd_record_mcount) \
220 scripts/basic/fixdep $(depfile) $@ '$(call make-cmd,cc_o_c)' > \
221 $(dot-target).tmp; \
222 rm -f $(depfile); \
223 mv -f $(dot-target).tmp
$(dot-target).cmd
224 endef
rule_cc_o_c
2.1 echo-cmd
&& cmd_checksrc :不执行
2.2 echo-cmd &&
cmd_cc_o_c :打印cmd_cc_o_c的内容,并执行cmd_cc_o_c将.c编译为.o
2.3 cmd_modversions :不执行
2.4 cmd_record_mcount :不执行
2.5 生成命令.cmd
下面逐条分析:
2.1-2.2 echo-cmd
&& cmd_checksrc 和 echo-cmd &&
cmd_cc_o_c
点击(此处)折叠或打开
linux-2.6.30.4/scripts/Kbuild.include
154 # echo command.
155 # Short version is used, if $(quiet) equals
`quiet_', otherwise full one.
156 echo-cmd = $(if $($(quiet)cmd_$(1)),\
157 echo ' $(call escsq,$($(quiet)cmd_$(1)))$(echo-why)';)
cmd_checksrc为空,不执行
linux-2.6.30.4/scripts/Makefile.build
178 ifndef CONFIG_MODVERSIONS
179 cmd_cc_o_c = $(CC) $(c_flags) -c -o $@ $<
$(call echo-cmd,cc_o_c)将执行的编译命令打印出来, $(cmd_cc_o_c)执行具体的编译命令。这将会在命令行中看到一坨坨的打印。
2.3 cmd_modversions
点击(此处)折叠或打开
linux-2.6.30.4/scripts/Makefile.build
178 ifndef CONFIG_MODVERSIONS
179 cmd_cc_o_c = $(CC) $(c_flags) -c -o $@ $<
180
181 else
194 cmd_cc_o_c = $(CC) $(c_flags) -c -o $(@D)/.tmp_$(@F) $<
195 cmd_modversions = ...
因为此处没有定义 CONFIG_MODVERSIONS, 所以cmd_modversions为空。
2.4 cmd_record_mcount
点击(此处)折叠或打开
208 ifdef CONFIG_FTRACE_MCOUNT_RECORD
209 cmd_record_mcount = perl $(srctree)/scripts/recordmcount.pl "$(ARCH)" \
210 "$(if $(CONFIG_64BIT),64,32)" \
211 "$(OBJDUMP)" "$(OBJCOPY)" "$(CC)" "$(LD)" "$(NM)" "$(RM)" "$(MV)" \
212 "$(if $(part-of-module),1,0)" "$(@)";
213 endif
CONFIG_FTRACE_MCOUNT_RECORD 没有定义,所以为空
总结一下:
虽然写了这么多,但是有用处的只有两个echo-cmd &&
cmd_cc_o_c和 mv ,打印cmd_cc_o_c的内容,并执行cmd_cc_o_c将.c编译为.o,把命令保存到.cmd文件中。假设让我自己写出来的Makefile可能也就是$(CC)
$(c_flags) -c -o $@ $<这么一句。
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