快速編寫“專家級”makefile（4.打造更專業的編譯環境——實現庫鏈接）

    根據前面所運行結果，main.o 被正確地生成了，但在鏈接時因爲找不到 foo() 函數的實現而出現錯誤。由於 foo() 函數的實現是放在 libfoo.a 庫中的，而 Makefile 中並沒有告訴編譯器在生成 huge.exe 時需要與 libfoo.a 庫鏈接在一起

    huge / build / make.rule

1. .PHONY : all clean
3. NKDIR = mkdir
4. RM = rm
5. RMFLAG = -rf
6. CC = gcc
7. AR = ar
8. ARFLAG = crs
10. DIR_OBJS = objs
11. DIR_EXES = $(ROOT)/build/exes
12. DIR_DEPS = deps
13. DIR_LIBS = $(ROOT)/build/libs
14. DIRS = $(DIR_OBJS) $(DIR_EXES) $(DIR_DEPS) $(DIR_LIBS)
15. RMS = $(DIR_OBJS) $(DIR_DEPS)
17. ifneq("$(EXE)", "")
18. EXE := $(addprefix $(DIR_EXES)/, $(EXE))
19. RMS += $(EXE)
20. endif
22. ifneq("$(LIB)", "")
23. LIB := $(addprefix $(DIR_LIBS)/, $(LIB))
24. RMS += $(LIB)
25. endif
27. SRCS = $(wildcard *.c)
28. OBJS = $(SRCS :.c = .o)
29. OBJS := $(addprefix $(DIR_OBJS)/, $(OBJS))
30. DEPS = $(SRCS :.c = .dep)
31. DEPS := $(addprefix $(DIR_DEPS)/, $(DEPS))
33. ifeq("$(wildcard $(DIR_OBJS))", "")
34. DEP_DIR_OBJS := $(DIR_OBJS)
35. endif
36. ifeq("$(wildcard $(DIR_EXES))", "")
37. DEP_DIR_EXES := $(DIR_EXES)
38. endif
39. ifeq("$(wildcard $(DIR_DEPS))", "")
40. DEP_DIR_DEPS := $(DIR_DEPS)
41. endif
42. ifeq("$(wildcard $(DIR_LIBS))", "")
43. DEP_DIR_LIBS := $(DIR_LIBS)
44. endif
46. all : $(EXE) $(LIB)
48. ifneq($MAKECMDGOALS, clean)
49. include $(DEPS)
50. endif
52. ifneq($(INCLUDE_DIRS), "")
53. INCLUDE_DIRS := $(strips $(INCLUDE_DIRS))
54. INCLUDE_DIRS := $(addprefix -I, $(INCLUDE_DIRS))
55. endif
57. ifneq($(LINK_LIBS), "")
58. LINK_LIBS := $(strip $(LINK_LIBS))
59. LINK_LIBS := $(addprefix -l, $(LINK_LIBS))
60. endif
62. $(DIRS) :
63. $(MKDIR) $@
65. $(EXE) : $(DEP_DIR_EXE) $(OBJS)
66. $(CC) -L$(DIR_LIBS) -o $@ $(filter %.o, $^)
68. $(LIB) : $(DEP_DIR_LIB) $(OBJS)
69. $(AR) $(ARFLAG) $@ $(filter %.o, $^)
71. $(DIR_OBJS) / %.o : $(DEP_DIR_OBJS) %.c
72. $(CC) $(INCLUDE_DIRS) -o $@ -c $(filter %.c, $^)
74. $(DIR_DEPS) / %.dep : $(DEP_DIR_DEPS) %.c
75. @echo "Creating $@ ..."
76. @set -e;\
77. $(RM) $(RMFLAG) $@.tmp;\
78. $(CC) $(INCLUDE_DIRS) -E -MM $(filter %.c, $^) > $@.tmp;\
79. sed 's,\(.*\)\.o[ :]*,objs/\1.o $@: ,g' < $@.tmp > $@;\
80. $(RM) $(RMFLAG) $@.tmp
82. clean :
83. $(RM) $(RMFLAG) $(RMS)

    huge / code / foo / src / Makefile

1. EXE =
3. LIB = libfoo.a
5. INCLUDE_DIRS = $(ROOT)/code/foo/inc
7. LINK_LIBS =
9. include $(ROOT)/build/make.rule

    huge / code / huge / src / Makefile

1. EXE = huge.exe
3. LIB =
5. INCLUDE_DIRS = $(ROOT)/code/foo/inc
7. LINK_LIBS = foo
9. include $(ROOT)/build/make.rule

    其中改動如下：

1. 增加 LINK_LIBS 變量， 用於存放可執行程序在鏈接時所需的所有庫
2. 將 $(DIR_LIBS) 通過 gcc 的 -L 選項加入到編譯器的庫搜索目錄列表中。在 huge 項目中，將所有的庫文件都放到 DIR_LIBS 目錄下，簡化了 Makefile 的實現
3. 在各模塊的 src 目錄下的 Makefile 中增加了 LINK_LIBS 變量的定義， 且在 code / huge / src / Makefile 中對 LINK_LIBS 賦值爲 foo。

    運行結果：

$ make

/Makefile/huge/build/make.rule:43: deps / foo.dep:No such file or directory

mkdir deps

Creating deps / foo.dep

mkdir objs

gcc -I/Makefile/huge/code/foo/libs/inc  -o  objs/foo.o  -c  foo.c

gcc -L/Makefile/huge/build/libs -o /Makefile/huge/build/exes/huge.exe  objs/main.o  -lfoo

$ $ROOT/build/exes/huge.exe

This is foo ()!

    

    現在，往 huge 項目中增加一個 bar 模塊，這個模塊將生成 libbar.a 靜態庫

    huge / code / bar / inc / bar.h

1. #ifndef __BAR_H
2. #define __BAR_H
4. void bar();
6. #endif

    huge / code / bar / inc / bar.c

1. #include <stdio.h>
2. #include "bar.h"
4. void bar()
5. {
6. printf("This is bar ()!\n");
7. }

    huge / code / bar / src / Makefile

1. EXE =
3. LIB = libbar.a
5. INCLUDE_DIRS = $(ROOT)/code/bar/inc
7. LINK_LIBS =
9. include $(ROOT)/build/make.rule

    新增目錄結構：

                        

    爲了構建 libbar.a，需要進入 code / bar / src 目錄並運行 make 命令

$ make

/Makefile/huge/build/make.rule:43: deps / bar.dep:No such file or directory

mkdir deps

Creating deps / bar.dep

mkdir objs

gcc -I/Makefile/huge/code/bar/libs/inc  -o  objs/bar.o  -c  bar.c

ar crs /Makefile/huge/build/libs/libbar.a   objs/bar.o

$ ls $ROOT/build/libs

libfoo.a  libbar.a

    在前面 code / huge / src / Makefile 的基礎上，作以下改動：

    huge / code / huge / src / main.c

1. #include "foo.h"
2. #include "bar.h"
4. int main()
5. {
6. foo();
7. bar();
8. return 0;
9. }

    huge / code / huge / src / Makefile

1. EXE = huge.exe
3. LIB =
5. INCLUDE_DIRS = $(ROOT)/code/foo/inc \
6. $(ROOT)/code/foo/inc
8. LINK_LIBS = foo bar
10. incldue $(ROOT)/build/make.rule

    運行結果：

/Makefile/huge/code/huge/src

$ make

Creating deps / main.dep ...

gcc -I/Makefile/huge/code/foo/inc  -I/Makefile/huge/code/bar/inc -o  objs/main.o  -c  main.c

gcc -L/Makefile/huge/build/libs -o /Makefile/huge/build/exes/huge.exe  objs/main.o  -lfoo -lbar

$ $ROOT/build/exes/huge.exe

This is foo ()!

This is bar()!

         參考文獻：《專業嵌入式軟件開發》李雲·著                                                2016年7月5日,星期二