uClinux上的应用程序设计-3

3 高效的程序开发

总的来说，在uClinux上的开发和标准Linux还是很类似的。通常可以按照下面的步骤去设计和调试：

建立基于以太网的开发环境；
如果所设计的程序和硬件的关联不大，那么一定要在标准Linux上先编译和调试通过。灵活地使用gcc和gdb将大大节省时间；
将x86上的GCC编译好的应用程序用交叉编译工具来编译；如果编译时发现错误，那么很可能存在以下问题：
- 交叉编译器或库文件的路径不正确；最彻底的解决办法是重新装一次编译器；
- 遇到库不支持的函数；此时需要自己把函数的实现做成另外一个库供应用程序使用。如果是uClinux本身不支持的调用，那么就需要改写代码了。
- C++的一些写法不太标准，需要修改；
通过网络(nfsmount)运行交叉编译成功的应用程序；
如果程序工作初步正常，那么就可以进一步在板子上测试了；否则，需做修改重新编译，尤其要检查与uClinux的内存特性有关的代码。

如果程序较小，设计时就可以比较灵活。如果是一个比较庞大的工程，那么，建立一个好的编译环境非常重要。下面，给出一个较为复杂的工程中所建立的一系列编译文件例子，用好它们可以提高效率。

例如，在编译x86平台上的程序时，可以这样输入：

>make config

出现提示：

Target Platform Selection

Choose a Vendor/Product combination.

Vendor/Product [Intel/i386| Motorola/M5307C3]

如果我们输入i386，那么就可以编译出PC上运行的程序；而输入M5307C3，就可以编译出uClinux上运行的程序。这对于经常需要在标准Linux和uClinux之间进行交叉编译和查找错误的程序来说非常方便。

首先，建立图 2所示的整个工程目录结构。

图 2 整个工程的目录结构

在config中，存放一些编译有关的配置文件；src目录下，按照各个程序模块分别创建一个目录。

在Project目录下，是整个工程的Makefile文件，如下：

###########################################################

# Makefile – Whole Project makefile.

###########################################################

# Get the core stuff worked out

ROOT_DIR = $(shell pwd)

SRC_DIR = $(ROOT_DIR)/src

CONFIG_DIR = $(ROOT_DIR)/config

SCRIPTS_DIR = $(ROOT_DIR)/scripts

CONFIG_SHELL := $(shell if [ -x "$$BASH" ]; then echo $$BASH; \

else if [ -x /bin/bash ]; then echo /bin/bash; \

else echo sh; fi ; fi)

TOPDIR := $(shell if [ "$$PWD" != "" ]; then echo $$PWD; else pwd; fi)

HPATH = $(TOPDIR)/include

FINDHPATH = $(HPATH)/asm $(HPATH)/linux $(HPATH)/scsi $(HPATH)/net

export ROOT_DIR SRC_DIR CONFIG_DIR SCRIPTS_DIR HPATH FINDHPATH

###########################################################

# normal make targets

.PHONY: all

all:

$(MAKE) -C $(SRC_DIR) all

###########################################################

# Config stuff, we recall ourselves to load the new config.arch before

# running the kernel and other config scripts

.PHONY: config

config: $(CONFIG_DIR)/config.in

cd $(CONFIG_DIR); $(CONFIG_SHELL) $(SCRIPTS_DIR)/Configure $(CONFIG_DIR)/config.in

@rm -f $(SRC_DIR)/arch.config

@if egrep "^CONFIG_DEFAULTS_INTEL_I386" $(CONFIG_DIR)/.config > /dev/null; then \

ln -s "$(CONFIG_DIR)/arch.i386" $(SRC_DIR)/arch.config; \

@if egrep "^CONFIG_DEFAULTS_MOTOROLA_M5272C3" $(CONFIG_DIR)/.config > /dev/null; then \

ln -s "$(CONFIG_DIR)/arch.m68k" $(SRC_DIR)/arch.config; \

@echo "#This dir.config file is automaticly generated by make config!" > $(SRC_DIR)/dir.config

@echo "ROOT_DIR="$(ROOT_DIR) >> $(SRC_DIR)/dir.config

@echo "CONFIG_DIR="$(CONFIG_DIR) >> $(SRC_DIR)/dir.config

@echo "SRC_DIR="$(SRC_DIR) >> $(SRC_DIR)/dir.config

@echo "SCRIPTS_DIR="$(SCRIPTS_DIR) >> $(SRC_DIR)/dir.config

@echo "HPATH="$(HPATH) >> $(SRC_DIR)/dir.config

@echo "FINDPATH="$(FINDPATH) >> $(SRC_DIR)/dir.config

###########################################################

# normal make dependancy

.PHONY: dep

dep:

$(MAKE) -C $(SRC_DIR) dep

# This one removes all executables from the tree and forces their relinking

clean:

$(MAKE) -C $(SRC_DIR) clean

test:

$(MAKE) -C $(SRC_DIR) test

run:

$(MAKE) -C $(SRC_DIR) run

config_error:

@echo "*************************************************"

@echo "You have not run make config."

@echo "The build sequence for this source tree is:"

@echo "1. 'make config' or 'make xconfig'"

@echo "2. 'make dep'"

@echo "3. 'make'"

@echo "*************************************************"

@exit 1

###########################################################

src目录下的Makefile文件，如下：

VERSION = 2

PATCHLEVEL = 0

SUBLEVEL = 39

UCRELEASE = uc2

.EXPORT_ALL_VARIABLES:

CONFIG_SHELL := $(shell if [ -x "$$BASH" ]; then echo $$BASH; \

else if [ -x /bin/bash ]; then echo /bin/bash; \

else echo sh; fi ; fi)

TOPDIR := $(shell if [ "$$PWD" != "" ]; then echo $$PWD; else pwd; fi)

TARGET = ESGateway

all: $(TARGET)

# Include the make variables (CC, etc...)

SUBDIRS = public serial packet cal xml fifo main interface

$(TARGET):

@set -e; for i in $(SUBDIRS); do $(MAKE) -C $$i all_targets; done

linuxsubdirs: dummy

set -e; for i in $(SUBDIRS); do $(MAKE) -C $$i; done

clean:

@set -e; for i in $(SUBDIRS); do $(MAKE) -C $$i clean; done

dep:

@set -e; for i in $(SUBDIRS); do $(MAKE) -C $$i fastdep; done

.PHONY: test

test:

@set -e; for i in $(SUBDIRS); do $(MAKE) -C $$i test; done

run:

# @set -e; for i in $(SUBDIRS); do $(MAKE) -i -C $$i run; read junk; done

make -C main run

src目录下的Rules.make文件给出了编译的一些规则，如下：

# This file contains rules which are shared between multiple Makefiles.

# False targets.

.PHONY: dummy

# Special variables which should not be exported

unexport EXTRA_ASFLAGS

unexport EXTRA_CFLAGS

ifneq "$(ARCH)" "h8300"

unexport EXTRA_LDFLAGS

endif

unexport EXTRA_ARFLAGS

unexport SUBDIRS

unexport SUB_DIRS

unexport ALL_SUB_DIRS

unexport MOD_SUB_DIRS

unexport O_TARGET

unexport O_OBJS

unexport L_OBJS

unexport M_OBJS

unexport MI_OBJS

unexport ALL_MOBJS

# objects that export symbol tables

unexport OX_OBJS

unexport LX_OBJS

unexport MX_OBJS

unexport MIX_OBJS

unexport SYMTAB_OBJS

unexport MOD_LIST_NAME

include ../dir.config

include $(SRC_DIR)/arch.config

# Get things started.

first_rule: sub_dirs

$(MAKE) all_targets

# Common rules

INC_DIR = -I$(SRC_DIR)/cal -I$(SRC_DIR)/xml -I$(SRC_DIR)/serial -I$(SRC_DIR)/packet -I$(SRC_DIR)/fifo -I$(SRC_DIR)/ping -I$(SRC_DIR)/interface -I$(SRC_DIR)/public

%.o: %.c

@echo "Compiling..."

@echo "$<"

$(CXX) $(INC_DIR) $(CFLAGS) $(EXTRA_CFLAGS) -c -o $@ $<

%.o: %.cpp

@echo "Compiling..."

@echo "$<"

$(CXX) $(INC_DIR) $(CFLAGS) $(EXTRA_CFLAGS) -c -o $@ $<

# Rule to compile a set of .o files into one .o file

ifeq (.depend,$(wildcard .depend))

include .depend

else

.depend: fastdep

endif

ifneq ($(O_TARGET),$(O_OBJS))

$(O_TARGET): .depend $(O_OBJS)

@echo "Linking..."

@echo $(O_OBJS) " --> " $@

@$(LD) $(EXTRA_LDFLAGS) -r -o $@ $(O_OBJS)

else

$(O_TARGET): .depend

endif

all: $(O_OBJS)

echo all

all_targets: $(O_OBJS) $(O_TARGET)

# Rule to compile a set of .o files into one .a file

ifdef L_TARGET

$(L_TARGET): $(LX_OBJS) $(L_OBJS)

rm -f $@

$(AR) $(EXTRA_ARFLAGS) rcs $@ $(LX_OBJS) $(L_OBJS)

endif

# This make dependencies quickly

fastdep: dummy

@echo "make fastdep"

if [ -n "$(wildcard *.[chS])" ]; then \

$(SCRIPTS_DIR)/mkdep *.[chS] > .depend; fi

if [ -n "$(wildcard *.cpp)" ]; then \

$(SCRIPTS_DIR)/mkdep *.cpp >> .depend; fi

# A rule to make subdirectories

sub_dirs: dummy

ifdef SUB_DIRS

set -e; for i in $(SUB_DIRS); do $(MAKE) -C $$i; done

endif

# A rule to do nothing

dummy:

config:

cd $(ROOT_DIR); make config

c clean:

rm -f *.o

rm -f *.gdb

rm -f .depend

rm -f test

rm -f core

rm -f *.elf

rm -f *.elf2flt

# This is useful for testing

script:

$(SCRIPT)

run: test

@echo ... running ...

@echo `pwd`/test

@./test

# This sets version suffixes on exported symbols

# Uses SYMTAB_OBJS

# Separate the object into "normal" objects and "exporting" objects

# Exporting objects are: all objects that define symbol tables

$(MX_OBJS):

$(CC) $(CFLAGS) -DEXPORT_SYMTAB -c $(@:.o=.c)

$(LX_OBJS) $(OX_OBJS):

$(CC) $(CFLAGS) -DMODVERSIONS -DEXPORT_SYMTAB -c $(@:.o=.c)

$(M_OBJS):

ifdef MAKING_MODULES

$(O_OBJS) $(L_OBJS):

endif

在config 目录下，编写两个和架构有关的文件，对于x86平台，是arch.i386，如下：

.EXPORT_ALL_VARIABLES:

###################################################################

# Vendor specific settings

CONSOLE_BAUD_RATE = 19200

###################################################################

# The makefiles need to know how to do things in different contexts

# To save some pain we put it all here

# First settings we always want for all build

# ARCH = kernel, TARGET_ARCH = uClibc

MACHINE = i386

ARCH = i386

CROSS_COMPILE =

CROSS = $(CROSS_COMPILE)

# We've used -m5307 here because the bulk of the 5272 instruction timings

# happen to be closer to the 5307 than the 5200 series. Luckily, the

# actual instructions on the two processors are essentially identical.

# This should be fixed at some stage.

CPUFLAGS =

CC = $(CROSS_COMPILE)gcc

AS = $(CROSS_COMPILE)as

CXX = $(CROSS_COMPILE)g++

AR = $(CROSS_COMPILE)ar

LD = $(CROSS_COMPILE)ld

OBJCOPY = $(CROSS_COMPILE)objcopy

RANLIB = $(CROSS_COMPILE)ranlib

STRIPTOOL = $(CROSS_COMPILE)strip

STRIP = $(STRIPTOOL)

UCLINUX_BUILD_SET = 0 # have we set a special config below

###################################################################

# General purpose lib building rules, uClibc.config uses these when

# possible

###################################################################

# Settings for building user apps

CFLAGS = -Wall -Wstrict-prototypes -O2 -g

#CFLAGS = -Wstrict-prototypes -g

LDFLAGS = -m elf_i386

###################################################################

# fall through, do other config options perhaps

ifeq ($(UCLINUX_BUILD_SET),1)

endif

###################################################################

在config 目录下，对于嵌入式平台，是arch.m68k，如下：

.EXPORT_ALL_VARIABLES:

###################################################################

# Vendor specific settings

CONSOLE_BAUD_RATE = 19200

###################################################################

# The makefiles need to know how to do things in different contexts

# To save some pain we put it all here

# First settings we always want for all build

# ARCH = kernel, TARGET_ARCH = uClibc

MACHINE = m68k

ARCH = m68knommu

CROSS_COMPILE = m68k-elf-

CROSS = $(CROSS_COMPILE)

# We've used -m5307 here because the bulk of the 5272 instruction timings

# happen to be closer to the 5307 than the 5200 series. Luckily, the

# actual instructions on the two processors are essentially identical.

# This should be fixed at some stage.

CPUFLAGS = -m5200

CC = $(CROSS_COMPILE)gcc

AS = $(CROSS_COMPILE)as

CXX = $(CROSS_COMPILE)g++

AR = $(CROSS_COMPILE)ar

LD = $(CROSS_COMPILE)ld

OBJCOPY = $(CROSS_COMPILE)objcopy

RANLIB = $(CROSS_COMPILE)ranlib

ELF2FLT = elf2flt

STRIPTOOL = $(CROSS_COMPILE)strip

STRIP = $(STRIPTOOL)

UCLINUX_BUILD_SET = 0 # have we set a special config below

###################################################################

# Settings for building user apps

#CFLAGS = -m5200 -msep-data -g

CFLAGS = -m5200 -msep-data

LDFLAGS = -Wl,-elf2flt

SYSLIBS = -lc -lstdc++ -lgcc

###################################################################

# fall through, do other config options perhaps

ifeq ($(UCLINUX_BUILD_SET),1)

endif

###################################################################

在config 目录下的config.in文件如下：

mainmenu_name 'uClinux Configuration'

mainmenu_option next_comment

comment 'Target Platform Selection'

comment 'Choose a Vendor/Product combination.'

choice 'Vendor/Product [Intel/i386 | Motorola/M5307C3] ' "1 CONFIG_DEFAULTS_INTEL_I386 \

2 CONFIG_DEFAULTS_MOTOROLA_M5307C3 \

" Intel/i386

endmenu

4 结语

本文讨论了uClinux平台上程序设计必须关注的一些特点，并对在uClinux进行高效程序开发做了一些讨论。

由于uClinux是开源的，在uClinux上的开发努力永远不会停止。世界范围的技术专家在使用uClinux来构造商业化的产品，他们的工作的重要部分反过来对开源的社区作出了贡献。每当我们访问uClinux的网站，看到又出现了更新的源码发布或者更好的工具时，就会感觉到这个开发团体的热情和能力，并鞭策自己努力工作，争取为这个自由软件的发展作出自己的创造性贡献。