linux/tools/build/Documentation/Build.txt
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   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
 116Fixdep
 117------
 118It is necessary to build the fixdep helper before invoking the build.
 119The Makefile.include file adds the fixdep target, that could be
 120invoked by the user.
 121
 122
 123Rules
 124-----
 125
 126The build framework provides standard compilation rules to handle .S and .c
 127compilation.
 128
 129It's possible to include special rule if needed (like we do for flex or bison
 130code generation).
 131
 132
 133CFLAGS
 134------
 135
 136It's possible to alter the standard object C flags in the following way:
 137
 138  CFLAGS_perf.o        += '...'  - adds CFLAGS for perf.o object
 139  CFLAGS_gtk           += '...'  - adds CFLAGS for gtk build object
 140  CFLAGS_REMOVE_perf.o += '...'  - removes CFLAGS for perf.o object
 141  CFLAGS_REMOVE_gtk    += '...'  - removes CFLAGS for gtk build object
 142
 143This C flags changes has the scope of the Build makefile they are defined in.
 144
 145
 146Dependencies
 147------------
 148
 149For each built object file 'a.o' the '.a.cmd' is created and holds:
 150
 151  - Command line used to built that object
 152    (for each object)
 153
 154  - Dependency rules generated by 'gcc -Wp,-MD,...'
 155    (for compiled object)
 156
 157All existing '.cmd' files are included in the Build process to follow properly
 158the dependencies and trigger a rebuild when necessary.
 159
 160
 161Single rules
 162------------
 163
 164It's possible to build single object file by choice, like:
 165
 166  $ make util/map.o    # objects
 167  $ make util/map.i    # preprocessor
 168  $ make util/map.s    # assembly
 169