1Build Framework
2===============
3
4The perf build framework was adopted from the kernel build system, hence the
5idea and the way how objects are built is the same.
6
7Basically the user provides set of 'Build' files that list objects and
8directories to nest for specific target to be build.
9
10Unlike the kernel we don't have a single build object 'obj-y' list that where
11we setup source objects, but we support more. This allows one 'Build' file to
12carry a sources list for multiple build objects.
13
14
15Build framework makefiles
16-------------------------
17
18The build framework consists of 2 Makefiles:
19
20  Build.include
21  Makefile.build
22
23While the 'Build.include' file contains just some generic definitions, the
24'Makefile.build' file is the makefile used from the outside. It's
25interface/usage is following:
26
27  $ make -f tools/build/Makefile.build srctree=$(KSRC) dir=$(DIR) obj=$(OBJECT)
28
29where:
30
31  KSRC   - is the path to kernel sources
32  DIR    - is the path to the project to be built
33  OBJECT - is the name of the build object
34
35When succefully finished the $(DIR) directory contains the final object file
36called $(OBJECT)-in.o:
37
38  $ ls $(DIR)/$(OBJECT)-in.o
39
40which includes all compiled sources described in 'Build' makefiles.
41
42
43Build makefiles
44---------------
45
46The user supplies 'Build' makefiles that contains a objects list, and connects
47the build to nested directories.
48
49Assume we have the following project structure:
50
51  ex/a.c
52    /b.c
53    /c.c
54    /d.c
55    /arch/e.c
56    /arch/f.c
57
58Out of which you build the 'ex' binary ' and the 'libex.a' library:
59
60  'ex'      - consists of 'a.o', 'b.o' and libex.a
61  'libex.a' - consists of 'c.o', 'd.o', 'e.o' and 'f.o'
62
63The build framework does not create the 'ex' and 'libex.a' binaries for you, it
64only prepares proper objects to be compiled and grouped together.
65
66To follow the above example, the user provides following 'Build' files:
67
68  ex/Build:
69    ex-y += a.o
70    ex-y += b.o
71    ex-y += b.o # duplicates in the lists are allowed
72
73    libex-y += c.o
74    libex-y += d.o
75    libex-y += arch/
76
77  ex/arch/Build:
78    libex-y += e.o
79    libex-y += f.o
80
81and runs:
82
83  $ make -f tools/build/Makefile.build dir=. obj=ex
84  $ make -f tools/build/Makefile.build dir=. obj=libex
85
86which creates the following objects:
87
88  ex/ex-in.o
89  ex/libex-in.o
90
91that contain request objects names in Build files.
92
93It's only a matter of 2 single commands to create the final binaries:
94
95  $ ar  rcs libex.a libex-in.o
96  $ gcc -o ex ex-in.o libex.a
97
98You can check the 'ex' example in 'tools/build/tests/ex' for more details.
99
100
101Makefile.include
102----------------
103
104The tools/build/Makefile.include makefile could be included
105via user makefiles to get usefull definitions.
106
107It defines following interface:
108
109  - build macro definition:
110      build := -f $(srctree)/tools/build/Makefile.build dir=. obj
111
112    to make it easier to invoke build like:
113      make $(build)=ex
114
115
116Rules
117-----
118
119The build framework provides standard compilation rules to handle .S and .c
120compilation.
121
122It's possible to include special rule if needed (like we do for flex or bison
123code generation).
124
125
126CFLAGS
127------
128
129It's possible to alter the standard object C flags in the following way:
130
131  CFLAGS_perf.o += '...' - alters CFLAGS for perf.o object
132  CFLAGS_gtk += '...'    - alters CFLAGS for gtk build object
133
134This C flags changes has the scope of the Build makefile they are defined in.
135
136
137Dependencies
138------------
139
140For each built object file 'a.o' the '.a.cmd' is created and holds:
141
142  - Command line used to built that object
143    (for each object)
144
145  - Dependency rules generated by 'gcc -Wp,-MD,...'
146    (for compiled object)
147
148All existing '.cmd' files are included in the Build process to follow properly
149the dependencies and trigger a rebuild when necessary.
150
151
152Single rules
153------------
154
155It's possible to build single object file by choice, like:
156
157  $ make util/map.o    # objects
158  $ make util/map.i    # preprocessor
159  $ make util/map.s    # assembly
160