makefile.txt

makefile文件的理解

on exported symbols 
# Separate the object into
"normal" objects and "exporting" objects 
# Exporting objects are: 
all objects that define symbol tables 
# 
ifdef CONFIG_MODULES 
# list-multi列出那些由
多个文件复合而成的模块； 
# 从编绎文件表和模块
文件表中过滤出复合模块名。 
multi-used := 
$(filter $(list-multi),
$(obj-y) $(obj-m)) 
# 取复合模块的构成表。 
multi-objs := $(foreach m,
$(multi-used), $($(basename $(m))-objs)) 
# 求出需进行编译的总模块表。 
active-objs := 
$(sort $(multi-objs) $(obj-y) $(obj-m)) 

ifdef CONFIG_MODVERSIONS 
ifneq "$(strip $(export-objs))" ""  
# 如果有需要进行版本化的文件。 
MODINCL = 
$(TOPDIR)/include/linux/modules 

# The -w option 
(enable warnings) for
genksyms will return here in 2.1 
# So where has it gone? 
# 
# Added the SMP separator 
to stop module accidents
between uniprocessor 
# and SMP Intel
boxes - AC - from bits by Michael Chastain 
# 

ifdef CONFIG_SMP 
genksyms_smp_prefix := -p smp_ 
else 
genksyms_smp_prefix :=  
endif 
# 从源文件计算版本文件的规则。 
$(MODINCL)/%.ver: %.c 
@if [ ! -r $
(MODINCL)/$*.stamp -o $(MODINCL)
/$*.stamp -ot $< ]; then \ 
echo '$(CC) $(CFLAGS) -E -D__GENKSYMS__ $<';
\ 
echo '| $(GENKSYMS) $(genksyms_smp_prefix) -k 
$(VERSION).$(PATCHLEVEL).$(SUBLEVEL) > $@.tmp';
\ 
$(CC) $(CFLAGS) -E -D__GENKSYMS__ $< 
\ 
| $(GENKSYMS) $(genksyms_smp_prefix) -k 
$(VERSION).$(PATCHLEVEL).$(SUBLEVEL) > $@.tmp; 
\ 
if [ -r $@ ] 
&& cmp -s $@ $@.tmp; 
then echo $@ is unchanged; rm -f 
$@.tmp; 
\ 
else echo mv $@.tmp $@; mv -f $@.tmp $@; fi; 
\ 
fi; touch $(MODINCL)/$*.stamp 
# 
将版本处理源文件的扩展名改为.ver，
并加上完整的路径名，
它们依赖于autoconf.h?br>?br>$(addprefix $(MODINCL)/,$(export-objs:.o=.ver)): 
$(TOPDIR)/include/linux/autoconf.h 

# updates .ver
files but not modversions.h 
# 通过fastdep，
逐个生成export-objs对应的版本文件。 
fastdep: $(addprefix $(MODINCL)/,
$(export-objs:.o=.ver)) 

# updates .ver files
and modversions.h like
before (is this needed?) 
# make dep过程的入口 
dep: fastdep update-modverfile 

endif # export-objs  

# update modversions.h,
but only if it would change 
# 刷新版本文件的过程。 
update-modverfile: 
@(echo "#ifndef _LINUX_MODVERSIONS_H";
\ 
  echo "#define _LINUX_MODVERSIONS_H"; 
  \ 
  echo "#include <linux/modsetver.h>";
  \ 
  cd $(TOPDIR)/include/linux/modules;
  \ 
  for f in *.ver; do 
  \ 
    if [ -f $$f ]; then echo "#include
	<linux/modules/$${f}>"; fi; 
	\ 
  done;
  \ 
  echo "#endif"; 
  \ 
) > $(TOPDIR)/include
/linux/modversions.h.tmp 
@if [ -r $(TOPDIR)/include
/linux/modversions.h ] 
&& cmp -s 
$(TOPDIR)/include/linux
/modversions.h 
$(TOPDIR)/include/linux
/modversions.h.tmp; then 
\ 
echo $(TOPDIR)/include/linux
/modversions.h was not updated;
\ 
rm -f $(TOPDIR)/include
/linux/modversions.h.tmp;
\ 
else
\ 
echo $(TOPDIR)/include
/linux/modversions.h was
updated; 
\ 
mv -f $(T
OPDIR)/include/linux
/modversions.h.tmp 
$(TOPDIR)/include
/linux/modversions.h; \ 
fi 
$(active-objs):
$(TOPDIR)/include/linux/modversions.h 

else 
# 如果没有配置版本化，modversions.h的内容。 
$(TOPDIR)/include/linux/modversions.h: 
@echo "#include <linux/modsetver.h>" > $@ 

endif # CONFIG_MODVERSIONS 

ifneq "$(strip $(export-objs))" "" 
# 版本化目标文件的编绎方法。 
$(export-objs): $(export-objs:.o=.c) $(TOPDIR)/include/linux/modversions.h 
$(CC) $(CFLAGS) 
$(EXTRA_CFLAGS)
$(CFLAGS_$@) -DEXPORT_SYMTAB -c
$(@:.o=.c) 
@ ( \ 
    echo 'ifeq ($(strip 
	$(subst $(comma),:,
	$(CFLAGS) $(EXTRA_CFLAGS) 
$(CFLAGS_$@) -DEXPORT_SYMTAB)),
$$(strip $$(subst $$(comma),:,
$$(CFLAGS) 
$$(EXTRA_CFLAGS)
$$(CFLAGS_$@) -DEXPORT_SYMTAB)))' 
; \ 
    echo 'FILES_FLAGS_UP_TO_DATE += 
	$@' ; \ 
    echo 'endif' \ 
) > $(dir $@)/.$(notdir $@).flags 
endif 

endif # CONFIG_MODULES 
# 
# include dependency files if they exist 
# 
# 嵌入源文件之间的依赖关系。 
ifneq ($(wildcard .depend),) 
include .depend 
endif 
# 嵌入头文件之间的依赖关系。 
ifneq ($(wildcard $(TOPDIR)
/.hdepend),) 
include $(TOPDIR)/.hdepend 
endif 

# 
# Find files whose 
flags have changed 
and force recompilation. 
# For safety, this works 
in the converse direction: 
#   every file is forced, 
except those whose flags
are positively 
up-to-date. 
# 
# 已经更新过的文件列表。 
FILES_FLAGS_UP_TO_DATE :=  

# For use in expunging 
commas from flags, which 
mung our checking. 
comma = , 
# 将当前目录下所有flags文件嵌入。 
FILES_FLAGS_EXIST := $(wildcard .*.flags) 
ifneq ($(FILES_FLAGS_EXIST),) 
include $(FILES_FLAGS_EXIST) 
endif 
# 将无需更新的文件从总的对象中删除。 
FILES_FLAGS_CHANGED := $(strip \ 
    $(filter-out $(FILES_FLAGS_UP_TO_DATE), \ 
$(O_TARGET) $(L_TARGET) $(active-objs) \ 
)) 

# A kludge: .S files don't get 
flag dependencies (yet), 
#   because that will involve 
changing a lot of Makefiles. 
Also 
#   suppress object files
explicitly listed in
$(IGNORE_FLAGS_OBJS). 
#   This allows handling 
of assembly files that get 
translated into 
#   multiple object files 
(see arch/ia64/lib/idiv.S, for example). 
#  
# 将由汇编文件生成的目件文件从
FILES_FLAGS_CHANGED删除。 
FILES_FLAGS_CHANGED := $(strip \ 
    $(filter-out $(patsubst %.S, %.o, $(wildcard *.S) 
$(IGNORE_FLAGS_OBJS)), \ 
    $(FILES_FLAGS_CHANGED))) 
# 将FILES_FLAGS_CHANGED设为目标。 
ifneq ($(FILES_FLAGS_CHANGED),) 
$(FILES_FLAGS_CHANGED): dummy 
endif 
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