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