Makefile與內核的編譯
1.在編譯內核出現如下錯誤信息
cc1: warnings being treated as errors註釋掉kernel根目錄下makefile文件中的-Werror-implicit-function-declaration語句即可。
2.如何根據內核的配置決定是否編譯某個文件中的某段代碼
我們知道，利用Makefile和Kconfig文件並make menuconfig，在編譯內核時可以決定哪些目錄或者文件將被編譯進內核映像。而在內核源碼中，該如何通過在Kconfig文件中定義的配置選項來決定是否編譯驅動源碼中的代碼呢？
如，我們在Kconfig文件中定義了config TOUCHSCREEN_XXX，則可在C源文件中做如下定義：
#if defined(CONFIG_TOUCHSCREEN_XXX)
.....
#endif這樣，在make menuconfig時，若選中了CONFIG_TOUCHSCREEN_XXX，則C文件中的這部分代碼就會被編譯，否則則不會被編譯。
那麼，在Kconfig文件中定義的CONFIG_TOUCHSCREEN_XXX是怎麼在C文件中發揮作用的呢？是這樣的，在make menuconfig之後，會生成.config文件，之後，scripts/kconfig會根據這個文件在include\generated目錄下生成autoconf.h文件，autoconf.h文件中就變成C語言可以識別的宏定義形式了，這樣就能夠決定C文件中哪部分代碼會被編譯。
3.幾種不同的賦值符號的作用
:= 覆蓋之前的值，賦予的值立刻生效+= 追加的意思，添加等號後面的值
?= 如果沒有被賦值過就賦予等號後面的值
4.轉載的一個編譯應用程序的通用Makefile
可以自動生成依賴關係文件，當修改頭文件後，make仍然能夠通過依賴關係重新進行編譯。
#############################################################################
#
# 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 <[email protected]>
# 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 =
# Specify the include dirs
INCLUDE = -I./src/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 = 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 = $(CC) $(DEP_OPT) $(EXTRA_CFLAGS) $(CFLAGS) $(CPPFLAGS)
DEPEND.d = $(subst -g ,,$(DEPEND))
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)
# 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 <[email protected]>'
@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.指定編譯鏈接的庫文件
-L 用於指定庫文件所在的路徑，比如-L./libs
-l 用於指定包含的庫文件，比如需要包含的庫文件爲libqrencode.so.3，則通過"-lqrencode"即可包含該庫，此處需要注意的是庫文件名要去掉”lib“和”so“。當需要鏈接線程庫時，可以通過-lpthread指定。
6.指定頭文件路徑
指定頭文件路徑可以通過參數-I，例如-I./inc。