[Feature] add GA346 baseline version
Change-Id: Ic62933698569507dcf98240cdf5d9931ae34348f
diff --git a/src/kernel/linux/v4.19/tools/build/Documentation/Build.txt b/src/kernel/linux/v4.19/tools/build/Documentation/Build.txt
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+Build Framework
+===============
+
+The perf build framework was adopted from the kernel build system, hence the
+idea and the way how objects are built is the same.
+
+Basically the user provides set of 'Build' files that list objects and
+directories to nest for specific target to be build.
+
+Unlike the kernel we don't have a single build object 'obj-y' list that where
+we setup source objects, but we support more. This allows one 'Build' file to
+carry a sources list for multiple build objects.
+
+
+Build framework makefiles
+-------------------------
+
+The build framework consists of 2 Makefiles:
+
+ Build.include
+ Makefile.build
+
+While the 'Build.include' file contains just some generic definitions, the
+'Makefile.build' file is the makefile used from the outside. It's
+interface/usage is following:
+
+ $ make -f tools/build/Makefile.build srctree=$(KSRC) dir=$(DIR) obj=$(OBJECT)
+
+where:
+
+ KSRC - is the path to kernel sources
+ DIR - is the path to the project to be built
+ OBJECT - is the name of the build object
+
+When succefully finished the $(DIR) directory contains the final object file
+called $(OBJECT)-in.o:
+
+ $ ls $(DIR)/$(OBJECT)-in.o
+
+which includes all compiled sources described in 'Build' makefiles.
+
+
+Build makefiles
+---------------
+
+The user supplies 'Build' makefiles that contains a objects list, and connects
+the build to nested directories.
+
+Assume we have the following project structure:
+
+ ex/a.c
+ /b.c
+ /c.c
+ /d.c
+ /arch/e.c
+ /arch/f.c
+
+Out of which you build the 'ex' binary ' and the 'libex.a' library:
+
+ 'ex' - consists of 'a.o', 'b.o' and libex.a
+ 'libex.a' - consists of 'c.o', 'd.o', 'e.o' and 'f.o'
+
+The build framework does not create the 'ex' and 'libex.a' binaries for you, it
+only prepares proper objects to be compiled and grouped together.
+
+To follow the above example, the user provides following 'Build' files:
+
+ ex/Build:
+ ex-y += a.o
+ ex-y += b.o
+ ex-y += b.o # duplicates in the lists are allowed
+
+ libex-y += c.o
+ libex-y += d.o
+ libex-y += arch/
+
+ ex/arch/Build:
+ libex-y += e.o
+ libex-y += f.o
+
+and runs:
+
+ $ make -f tools/build/Makefile.build dir=. obj=ex
+ $ make -f tools/build/Makefile.build dir=. obj=libex
+
+which creates the following objects:
+
+ ex/ex-in.o
+ ex/libex-in.o
+
+that contain request objects names in Build files.
+
+It's only a matter of 2 single commands to create the final binaries:
+
+ $ ar rcs libex.a libex-in.o
+ $ gcc -o ex ex-in.o libex.a
+
+You can check the 'ex' example in 'tools/build/tests/ex' for more details.
+
+
+Makefile.include
+----------------
+
+The tools/build/Makefile.include makefile could be included
+via user makefiles to get usefull definitions.
+
+It defines following interface:
+
+ - build macro definition:
+ build := -f $(srctree)/tools/build/Makefile.build dir=. obj
+
+ to make it easier to invoke build like:
+ make $(build)=ex
+
+
+Fixdep
+------
+It is necessary to build the fixdep helper before invoking the build.
+The Makefile.include file adds the fixdep target, that could be
+invoked by the user.
+
+
+Rules
+-----
+
+The build framework provides standard compilation rules to handle .S and .c
+compilation.
+
+It's possible to include special rule if needed (like we do for flex or bison
+code generation).
+
+
+CFLAGS
+------
+
+It's possible to alter the standard object C flags in the following way:
+
+ CFLAGS_perf.o += '...' - adds CFLAGS for perf.o object
+ CFLAGS_gtk += '...' - adds CFLAGS for gtk build object
+ CFLAGS_REMOVE_perf.o += '...' - removes CFLAGS for perf.o object
+ CFLAGS_REMOVE_gtk += '...' - removes CFLAGS for gtk build object
+
+This C flags changes has the scope of the Build makefile they are defined in.
+
+
+Dependencies
+------------
+
+For each built object file 'a.o' the '.a.cmd' is created and holds:
+
+ - Command line used to built that object
+ (for each object)
+
+ - Dependency rules generated by 'gcc -Wp,-MD,...'
+ (for compiled object)
+
+All existing '.cmd' files are included in the Build process to follow properly
+the dependencies and trigger a rebuild when necessary.
+
+
+Single rules
+------------
+
+It's possible to build single object file by choice, like:
+
+ $ make util/map.o # objects
+ $ make util/map.i # preprocessor
+ $ make util/map.s # assembly