文章目录
- 1. 目标 $(obj)/fixdep
- 1.1 cmd_host-csingle函数分析：
1 # SPDX-License-Identifier: GPL-2.0
2 # ==========================================================================
3 # Building binaries on the host system
4 # Binaries are used during the compilation of the kernel, for example
5 # to preprocess a data file.
6 #
7 # Both C and C++ are supported, but preferred language is C for such utilities.
8 #
9 # Sample syntax (see Documentation/kbuild/makefiles.txt for reference)
10 # hostprogs-y := bin2hex
11 # Will compile bin2hex.c and create an executable named bin2hex
12 #
13 # hostprogs-y := lxdialog
14 # lxdialog-objs := checklist.o lxdialog.o
15 # Will compile lxdialog.c and checklist.c, and then link the executable
16 # lxdialog, based on checklist.o and lxdialog.o
17 #
18 # hostprogs-y := qconf
19 # qconf-cxxobjs := qconf.o
20 # qconf-objs := menu.o
21 # Will compile qconf as a C++ program, and menu as a C program.
22 # They are linked as C++ code to the executable qconf
23
24 __hostprogs := $(sort $(hostprogs-y) $(hostprogs-m))
25 host-cshlib := $(sort $(hostlibs-y) $(hostlibs-m))
26 host-cxxshlib := $(sort $(hostcxxlibs-y) $(hostcxxlibs-m))
27
28 # C code
29 # Executables compiled from a single .c file
30 host-csingle := $(foreach m,$(__hostprogs), \
31 $(if $($(m)-objs)$($(m)-cxxobjs)$($(m)-sharedobjs),,$(m)))
32
33 # C executables linked based on several .o files
34 host-cmulti := $(foreach m,$(__hostprogs),\
35 $(if $($(m)-cxxobjs),,$(if $($(m)-objs),$(m))))
36
37 # Shared object libraries
38 host-shared := $(foreach m,$(__hostprogs),\
39 $(if $($(m)-sharedobjs),$(m))))
40
41 # Object (.o) files compiled from .c files
42 host-cobjs := $(sort $(foreach m,$(__hostprogs),$($(m)-objs)))
43
44 # C++ code
45 # C++ executables compiled from at least one .cc file
46 # and zero or more .c files
47 host-cxxmulti := $(foreach m,$(__hostprogs),$(if $($(m)-cxxobjs),$(m)))
48
49 # C++ Object (.o) files compiled from .cc files
50 host-cxxobjs := $(sort $(foreach m,$(host-cxxmulti),$($(m)-cxxobjs)))
51
52 # Object (.o) files used by the shared libaries
53 host-cshobjs := $(sort $(foreach m,$(host-cshlib),$($(m:.so=-objs))))
54 host-cxxshobjs := $(sort $(foreach m,$(host-cxxshlib),$($(m:.so=-objs))))
55
56 host-csingle := $(addprefix $(obj)/,$(host-csingle))
57 host-cmulti := $(addprefix $(obj)/,$(host-cmulti))
58 host-cobjs := $(addprefix $(obj)/,$(host-cobjs))
59 host-cxxmulti := $(addprefix $(obj)/,$(host-cxxmulti))
60 host-cxxobjs := $(addprefix $(obj)/,$(host-cxxobjs))
61 host-cshlib := $(addprefix $(obj)/,$(host-cshlib))
62 host-cxxshlib := $(addprefix $(obj)/,$(host-cxxshlib))
63 host-cshobjs := $(addprefix $(obj)/,$(host-cshobjs))
64 host-cxxshobjs := $(addprefix $(obj)/,$(host-cxxshobjs))
65 host-shared := $(addprefix $(obj)/,$(host-shared))
66
67 #####
68 # Handle options to gcc. Support building with separate output directory
69
70 _hostc_flags = $(KBUILD_HOSTCFLAGS) $(HOST_EXTRACFLAGS) \
71 $(HOSTCFLAGS_$(basetarget).o)
72 _hostcxx_flags = $(KBUILD_HOSTCXXFLAGS) $(HOST_EXTRACXXFLAGS) \
73 $(HOSTCXXFLAGS_$(basetarget).o)
74
75 ifeq ($(KBUILD_SRC),)
76 __hostc_flags = $(_hostc_flags)
77 __hostcxx_flags = $(_hostcxx_flags)
78 else
79 __hostc_flags = -I$(obj) $(call flags,_hostc_flags)
80 __hostcxx_flags = -I$(obj) $(call flags,_hostcxx_flags)
81 endif
82
83 hostc_flags = -Wp,-MD,$(depfile) $(__hostc_flags)
84 hostcxx_flags = -Wp,-MD,$(depfile) $(__hostcxx_flags)
85
86 #####
87 # Compile programs on the host
88
89 # Create executable from a single .c file
90 # host-csingle -> Executable
91 quiet_cmd_host-csingle = HOSTCC $@
92 cmd_host-csingle = $(HOSTCC) $(hostc_flags) -o $@ $< \
93 $(KBUILD_HOSTLDLIBS) $(HOSTLDLIBS_$(@F))
94 $(host-csingle): $(obj)/%: $(src)/%.c FORCE
95 $(call if_changed_dep,host-csingle)
96
97 # Link an executable based on list of .o files, all plain c
98 # host-cmulti -> executable
99 quiet_cmd_host-cmulti = HOSTLD $@
100 cmd_host-cmulti = $(HOSTCC) $(KBUILD_HOSTLDFLAGS) -o $@ \
101 $(addprefix $(obj)/,$($(@F)-objs)) \
102 $(KBUILD_HOSTLDLIBS) $(HOSTLDLIBS_$(@F))
103 $(host-cmulti): FORCE
104 $(call if_changed,host-cmulti)
105 $(call multi_depend, $(host-cmulti), , -objs)
106
107 # Create .o file from a single .c file
108 # host-cobjs -> .o
109 quiet_cmd_host-cobjs = HOSTCC $@
110 cmd_host-cobjs = $(HOSTCC) $(hostc_flags) -c -o $@ $<
111 $(host-cobjs): $(obj)/%.o: $(src)/%.c FORCE
112 $(call if_changed_dep,host-cobjs)
113
114 # Link an executable based on list of .o files, a mixture of .c and .cc
115 # host-cxxmulti -> executable
116 quiet_cmd_host-cxxmulti = HOSTLD $@
117 cmd_host-cxxmulti = $(HOSTCXX) $(KBUILD_HOSTLDFLAGS) -o $@ \
118 $(foreach o,objs cxxobjs,\
119 $(addprefix $(obj)/,$($(@F)-$(o)))) \
120 $(KBUILD_HOSTLDLIBS) $(HOSTLDLIBS_$(@F))
121 $(host-cxxmulti): FORCE
122 $(call if_changed,host-cxxmulti)
123 $(call multi_depend, $(host-cxxmulti), , -objs -cxxobjs)
124
125 # Create .o file from a single .cc (C++) file
126 quiet_cmd_host-cxxobjs = HOSTCXX $@
127 cmd_host-cxxobjs = $(HOSTCXX) $(hostcxx_flags) -c -o $@ $<
128 $(host-cxxobjs): $(obj)/%.o: $(src)/%.cc FORCE
129 $(call if_changed_dep,host-cxxobjs)
130
131 # Compile .c file, create position independent .o file
132 # host-cshobjs -> .o
133 quiet_cmd_host-cshobjs = HOSTCC -fPIC $@
134 cmd_host-cshobjs = $(HOSTCC) $(hostc_flags) -fPIC -c -o $@ $<
135 $(host-cshobjs): $(obj)/%.o: $(src)/%.c FORCE
136 $(call if_changed_dep,host-cshobjs)
137
138 # Compile .c file, create position independent .o file
139 # Note that plugin capable gcc versions can be either C or C++ based
140 # therefore plugin source files have to be compilable in both C and C++ mode.
141 # This is why a C++ compiler is invoked on a .c file.
142 # host-cxxshobjs -> .o
143 quiet_cmd_host-cxxshobjs = HOSTCXX -fPIC $@
144 cmd_host-cxxshobjs = $(HOSTCXX) $(hostcxx_flags) -fPIC -c -o $@ $<
145 $(host-cxxshobjs): $(obj)/%.o: $(src)/%.c FORCE
146 $(call if_changed_dep,host-cxxshobjs)
147
148 # Link a shared library, based on position independent .o files
149 # *.o -> .so shared library (host-cshlib)
150 quiet_cmd_host-cshlib = HOSTLLD -shared $@
151 cmd_host-cshlib = $(HOSTCC) $(HOSTLDFLAGS) -shared -o $@ \
152 $(addprefix $(obj)/,$($(@F:.so=-objs))) \
153 $(HOST_LOADLIBES) $(HOSTLDLIBS_$(@F))
154 $(host-cshlib): FORCE
155 $(call if_changed,host-cshlib)
156 $(call multi_depend, $(host-cshlib), .so, -objs)
157
158 # Link a shared library, based on position independent .o files
159 # *.o -> .so shared library (host-cxxshlib)
160 quiet_cmd_host-cxxshlib = HOSTLLD -shared $@
161 cmd_host-cxxshlib = $(HOSTCXX) $(HOSTLDFLAGS) -shared -o $@ \
162 $(addprefix $(obj)/,$($(@F:.so=-objs))) \
163 $(HOST_LOADLIBES) $(HOSTLDLIBS_$(@F))
164 $(host-cxxshlib): FORCE
165 $(call if_changed,host-cxxshlib)
166 $(call multi_depend, $(host-cxxshlib), .so, -objs)
167
168 targets += $(host-csingle) $(host-cmulti) $(host-cobjs)\
169 $(host-cxxmulti) $(host-cxxobjs) $(host-shared) \
170 $(host-cshlib) $(host-cshobjs) $(host-cxxshlib) $(host-cxxshobjs)
171
1. 目标 $(obj)/fixdep
由于目标是 $(obj)/fixdep，所以自动匹配第94-95行：
94 $(host-csingle): $(obj)/%: $(src)/%.c FORCE 95 $(call if_changed_dep,host-csingle)1.第94行中的 $(host-csingle) 在第24-56行中定义：
24 __hostprogs := $(sort $(hostprogs-y) $(hostprogs-m)) 30 host-csingle := $(foreach m,$(__hostprogs), \ 31 $(if $($(m)-objs)$($(m)-cxxobjs)$($(m)-sharedobjs),,$(m))) 56 host-csingle := $(addprefix $(obj)/,$(host-csingle))addprefix函数、sort函数、foreach函数
第24行：由于顶层 Makefile 中执行make -f ./scripts/Makefile.build obj=scripts/basic，又在 Makefile.build 中第57行引用scripts/basic/Makefile，在 scripts/basic/Makefile 中定义hostprogs-y := fixdep，hostprogs-m 未定义，所以最终： __hostprogs = fixdep
第30行：由于第24行的变量定义，所以最终： host-csingle = fixdep
第56行：由第30行定义，所以最终： host-csingle = $(obj)/fixdep
2.第94行中的 $(obj) 和 $(src) 在 scripts/Makefile.build 的第7-15行中定义，所以最终： $(obj) = $(src)7 prefix := tpl 8 src := $(patsubst $(prefix)/%,%,$(obj)) 9 ifeq ($(obj),$(src)) 10 prefix := spl 11 src := $(patsubst $(prefix)/%,%,$(obj)) 12 ifeq ($(obj),$(src)) 13 prefix := . 14 endif 15 endif第94-95行最终展开为：
94 $(obj)/fixdep: $(obj)/%: $(obj)/%.c FORCE 95 $(call if_changed_dep,host-csingle)这里目标
$(obj)/fixdep的生成，依赖$(src)/%.c，其目录下存在此类文件【fixdep.c】，经过 if_changed_dep函数 分析，第95行实际是打印并执行cmd_host-csingle函数，并将相应内容输入到$(obj)/.fixdep.cmd文件中。
最终：打印并执行$(cmd_host-csingle)命令，并将cmd_$@ ：= $(cmd_host-csingle)的内容输入到$(obj)/.$@.cmd文件中，完成最终目标的生成【即生成 scripts/basic/fixdep】92 cmd_host-csingle = cc -Wp,-MD,scripts/basic/.fixdep.d -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer -std=gnu11 -o scripts/basic/fixdep scripts/basic/fixdep.c 94 scripts/basic/fixdep: scripts/basic/fixdep: scripts/basic/fixdep.c FORCE 95 $(cmd_host-csingle)
1.1 cmd_host-csingle函数分析：
91 quiet_cmd_host-csingle = HOSTCC $@ 92 cmd_host-csingle = $(HOSTCC) $(hostc_flags) -o $@ $< \ 93 $(KBUILD_HOSTLDLIBS) $(HOSTLDLIBS_$(@F))第92行：$(HOSTCC) 在顶层 Makefile 的282行定义 HOSTCC = cc
第92行：$(hostc_flags) 在83行定义：70 _hostc_flags = $(KBUILD_HOSTCFLAGS) $(HOST_EXTRACFLAGS) \ 71 $(HOSTCFLAGS_$(basetarget).o) 72 _hostcxx_flags = $(KBUILD_HOSTCXXFLAGS) $(HOST_EXTRACXXFLAGS) \ 73 $(HOSTCXXFLAGS_$(basetarget).o) 74 75 ifeq ($(KBUILD_SRC),) 76 __hostc_flags = $(_hostc_flags) 77 __hostcxx_flags = $(_hostcxx_flags) 78 else 79 __hostc_flags = -I$(obj) $(call flags,_hostc_flags) 80 __hostcxx_flags = -I$(obj) $(call flags,_hostcxx_flags) 81 endif 82 83 hostc_flags = -Wp,-MD,$(depfile) $(__hostc_flags) 84 hostcxx_flags = -Wp,-MD,$(depfile) $(__hostcxx_flags) ...... 83 hostc_flags = -Wp,-MD,$(depfile) $(__hostc_flags)第83行：$(depfile) 在scripts/Kbuild.include 【在顶层Makefile的396行引用】的20行定义：
最终： depfile = $(obj)/.$(notdir $@).cmd
dir函数、notdir 函数、subst 函数5 comma := , 15 dot-target = $(dir $@).$(notdir $@) 20 depfile = $(subst $(comma),_,$(dot-target).d)第83行：$(__hostc_flags)，当输入
make O=dir时，KBUILD_SRC=dir，由于这里没有O=，所以第75行条件成立，执行第76行，第76行中的 $(_hostc_flags) 在第70行中定义，其中的$(HOST_EXTRACFLAGS)和$(HOSTCFLAGS_$(basetarget).o)未定义为空，$(KBUILD_HOSTCFLAGS)在顶层 Makefile 中定义为:-Wall -Wstrict-prototypes -O2 -fomit-frame-pointer -std=gnu11
最终： hostc_flags = -Wp,-MD,scripts/basic/.fixdep.d -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer -std=gnu11第93行：@F介绍，
$(KBUILD_HOSTLDLIBS)和$(HOSTLDLIBS_$(@F)未定义为空
最终：cmd_host-csingle = cc -Wp,-MD,$(obj).$(notdir $@).cmd -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer -std=gnu11 -o $@ $<
-总结篇)