Makefile与内核的编译

Makefile与内核的编译

1.在编译内核出现如下错误信息

cc1: warnings being treated as errors

注释掉kernel根目录下makefile文件中的-Werror-implicit-function-declaration语句即可。

2.如何根据内核的配置决定是否编译某个文件中的某段代码

我们知道，利用Makefile和Kconfig文件并make menuconfig，在编译内核时可以决定哪些目录或者文件将被编译进内核映像。而在内核源码中，该如何通过在Kconfig文件中定义的配置选项来决定是否编译驱动源码中的代码呢？
如，我们在Kconfig文件中定义了config TOUCHSCREEN_XXX，则可在C源文件中做如下定义：

#if defined(CONFIG_TOUCHSCREEN_XXX)
.....
#endif

这样，在make menuconfig时，若选中了CONFIG_TOUCHSCREEN_XXX，则C文件中的这部分代码就会被编译，否则则不会被编译。
那么，在Kconfig文件中定义的CONFIG_TOUCHSCREEN_XXX是怎么在C文件中发挥作用的呢？是这样的，在make menuconfig之后，会生成.confi文件，之后，scripts/kconfig会根据这个文件在include\generated目录下生成autoconf.h文件，autoconf.h文件中就编程C语言可以识别的宏定义形式了，这样就能够决定C文件中那部分代码会被编译。

3.几种不同的赋值符号的作用

:= 覆盖之前的值，赋予的值立刻生效
+= 追加的意思，添加等号后面的值
?= 如果没有被赋值过就赋予等号后面的值

4.转载的一个编译应用程序的通用Makefile

#############################################################################
#
# Generic Makefile for C/C++ Program
#
# License: GPL (General Public License)
# Author:  whyglinux <whyglinux AT gmail DOT com>
# Date:    2006/03/04 (version 0.1)
#          2007/03/24 (version 0.2)
#          2007/04/09 (version 0.3)
#          2007/06/26 (version 0.4)
#          2008/04/05 (version 0.5)
#
# Author: kevin1078 <kevin1078@126.com>
# Date:    2012/04/24 (version 0.6)
#===========================================================================

## Customizable Section: adapt those variables to suit your program.
##==========================================================================

# The extra pre-processor and compiler options.
EXTRA_CFLAGS =

# The extra linker options.
EXTRA_LDFLAGS   = -lpthread

# Specify the include dirs
INCLUDE   = -I./inc

# The pre-processor options used by the cpp (man cpp for more).
CPPFLAGS  = -Wall $(INCLUDE)

# The options used in linking as well as in any direct use of ld.
LDFLAGS   =

# The directories in which source files reside.
# If not specified, all subdirectories of the current directory will be serached.
SRCDIRS   :=

# The executable file name. Must be specified.
PROGRAM   = B3_app

## Implicit Section: change the following only when necessary.
##==========================================================================

# The source file types (headers excluded).
# .c indicates C source files, and others C++ ones.
SRCEXTS = .c .C .cc .cpp .CPP .c++ .cxx .cp

# The header file types.
HDREXTS = .h .H .hh .hpp .HPP .h++ .hxx .hp

# The pre-processor and compiler options.
# Users can override those variables from the command line.
CFLAGS  = -g -O2
CXXFLAGS= -g -O2

# The C program compiler.
CC     = mipsel-linux-gcc

# The C++ program compiler.
CXX    = g++

# Un-comment the following line to compile C programs as C++ ones.
#CC     = $(CXX)

# The command used to delete file.
RM     = rm -f

ETAGS = etags
ETAGSFLAGS =

CTAGS = ctags
CTAGSFLAGS =

## Stable Section: usually no need to be changed. But you can add more.
##==========================================================================
ifeq ($(SRCDIRS),)
  SRCDIRS := $(shell find $(SRCDIRS) -type d)
endif
SOURCES = $(foreach d,$(SRCDIRS),$(wildcard $(addprefix $(d)/*,$(SRCEXTS))))
HEADERS = $(foreach d,$(SRCDIRS),$(wildcard $(addprefix $(d)/*,$(HDREXTS))))
SRC_CXX = $(filter-out %.c,$(SOURCES))
OBJS    = $(addsuffix .o, $(basename $(SOURCES)))
#DEPS    = $(OBJS:%.o=%.d) #replace %.d with .%.d (hide dependency files)
DEPS    = $(foreach f, $(OBJS), $(addprefix $(dir $(f))., $(patsubst %.o, %.d, $(notdir $(f)))))



## Define some useful variables.
DEP_OPT = $(shell if `$(CC) --version | grep -i "GCC" >/dev/null`; then \
                  echo "-MM"; else echo "-M"; fi )
DEPEND.d      = $(CC)  $(DEP_OPT)  $(EXTRA_CFLAGS) $(CFLAGS) $(CPPFLAGS)
COMPILE.c   = $(CC)  $(EXTRA_CFLAGS) $(CFLAGS)   $(CPPFLAGS) -c
COMPILE.cxx = $(CXX) $(EXTRA_CFLAGS) $(CXXFLAGS) $(CPPFLAGS) -c
LINK.c      = $(CC)  $(EXTRA_CFLAGS) $(CFLAGS)   $(CPPFLAGS) $(LDFLAGS)
LINK.cxx    = $(CXX) $(EXTRA_CFLAGS) $(CXXFLAGS) $(CPPFLAGS) $(LDFLAGS)

.PHONY: all objs tags ctags clean distclean help show

# Delete the default suffixes
.SUFFIXES:

all: $(PROGRAM)
	cp $(PROGRAM) ../rootfs/usr/neolix

# Rules for creating dependency files (.d).
#------------------------------------------

.%.d:%.c
	@echo -n $(dir $<) > $@
	@$(DEPEND.d) $< >> $@

.%.d:%.C
	@echo -n $(dir $<) > $@
	@$(DEPEND.d) $< >> $@

.%.d:%.cc
	@echo -n $(dir $<) > $@
	@$(DEPEND.d) $< >> $@

.%.d:%.cpp
	@echo -n $(dir $<) > $@
	@$(DEPEND.d) $< >> $@

.%.d:%.CPP
	@echo -n $(dir $<) > $@
	@$(DEPEND.d) $< >> $@

.%.d:%.c++
	@echo -n $(dir $<) > $@
	@$(DEPEND.d) $< >> $@

.%.d:%.cp
	@echo -n $(dir $<) > $@
	@$(DEPEND.d) $< >> $@

.%.d:%.cxx
	@echo -n $(dir $<) > $@
	@$(DEPEND.d) $< >> $@

# Rules for generating object files (.o).
#----------------------------------------
objs:$(OBJS)

%.o:%.c
	$(COMPILE.c) $< -o $@

%.o:%.C
	$(COMPILE.cxx) $< -o $@

%.o:%.cc
	$(COMPILE.cxx) $< -o $@

%.o:%.cpp
	$(COMPILE.cxx) $< -o $@

%.o:%.CPP
	$(COMPILE.cxx) $< -o $@

%.o:%.c++
	$(COMPILE.cxx) $< -o $@

%.o:%.cp
	$(COMPILE.cxx) $< -o $@

%.o:%.cxx
	$(COMPILE.cxx) $< -o $@

# Rules for generating the tags.
#-------------------------------------
tags: $(HEADERS) $(SOURCES)
	$(ETAGS) $(ETAGSFLAGS) $(HEADERS) $(SOURCES)

ctags: $(HEADERS) $(SOURCES)
	$(CTAGS) $(CTAGSFLAGS) $(HEADERS) $(SOURCES)

# Rules for generating the executable.
#-------------------------------------
$(PROGRAM):$(OBJS)
ifeq ($(SRC_CXX),)              # C program
	$(LINK.c)   $(OBJS) $(EXTRA_LDFLAGS) -o $@
	@echo Type ./$@ to execute the program.
else                            # C++ program
	$(LINK.cxx) $(OBJS) $(EXTRA_LDFLAGS) -o $@
	@echo Type ./$@ to execute the program.
endif

#ifndef NODEP
#ifneq ($(DEPS),)
#	sinclude $(DEPS)
#endif
#endif

clean:
	$(RM) $(OBJS) $(PROGRAM) $(PROGRAM).exe

distclean: clean
	$(RM) $(DEPS) TAGS

# Show help.
help:
	@echo 'Generic Makefile for C/C++ Programs (gcmakefile) version 0.5'
	@echo 'Copyright (C) 2007, 2008 whyglinux <whyglinux@hotmail.com>'
	@echo
	@echo 'Usage: make [TARGET]'
	@echo 'TARGETS:'
	@echo '  all       (=make) compile and link.'
	@echo '  NODEP=yes make without generating dependencies.'
	@echo '  objs      compile only (no linking).'
	@echo '  tags      create tags for Emacs editor.'
	@echo '  ctags     create ctags for VI editor.'
	@echo '  clean     clean objects and the executable file.'
	@echo '  distclean clean objects, the executable and dependencies.'
	@echo '  show      show variables (for debug use only).'
	@echo '  help      print this message.'
	@echo
	@echo 'Report bugs to <whyglinux AT gmail DOT com>.'

# Show variables (for debug use only.)
show:
	@echo 'PROGRAM     :' $(PROGRAM)
	@echo 'SRCDIRS     :' $(SRCDIRS)
	@echo 'HEADERS     :' $(HEADERS)
	@echo 'SOURCES     :' $(SOURCES)
	@echo 'SRC_CXX     :' $(SRC_CXX)
	@echo 'OBJS        :' $(OBJS)
	@echo 'DEPS        :' $(DEPS)
	@echo 'DEPEND      :' $(DEPEND)
	@echo 'DEPEND.d    :' $(DEPEND.d)
	@echo 'COMPILE.c   :' $(COMPILE.c)
	@echo 'COMPILE.cxx :' $(COMPILE.cxx)
	@echo 'link.c      :' $(LINK.c)
	@echo 'link.cxx    :' $(LINK.cxx)

## End of the Makefile ##  Suggestions are welcome  ## All rights reserved ##
#############################################################################

5.指定编译链接的库文件

-L 用于指定库文件所在的路径，比如-L./libs

-l  用于指定包含的库文件，比如需要包含的库文件为libqrencode.so.3，则通过"-lqrencode"即可包含该库，此处需要注意的是库文件名要去掉”lib“和”so“。当需要链接线程库时，可以通过-lpthread指定。

6.指定头文件路径

指定头文件路径可以通过参数-I，例如-I./inc。