tools build: Add new build support

Adding new build framework into 'tools/build' to be used by tools.

There's no change for actual building at this point, it comes in the
next patches.

The idea and more details are explained in the
'tools/build/Documentation/Build.txt' file.

I adopted everything from the kernel build system, with some changes to
allow for multiple binaries build definitions.

While the kernel's build output is single image (forget modules) we need
to be able to build several binaries/libraries.

The basic idea is that sser provides 'Build' files with objects
definitions like:

  perf-y += a.o
  perf-y += b.o
  libperf-y += c.o
  libperf-y += d.o

and the build framework outputs files:

  perf-in.o    # a.o, b.o compiled in
  libperf-in.o # c.o, d.o compiled in

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Tested-by: Will Deacon <will.deacon@arm.com>
Cc: Alexis Berlemont <alexis.berlemont@gmail.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-fbj22h4av0otlxupwcmrxgpa@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 139 insertions, 0 deletions

diff --git a/tools/build/Documentation/Build.txt b/tools/build/Documentation/Build.txt
new file mode 100644
index 000000000000..00ad2d608727
--- /dev/null
+++ b/tools/build/Documentation/Build.txt
@@ -0,0 +1,139 @@
+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.
+
+a) 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 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.
+
+a) 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
+
+    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.
+
+b) 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).
+
+c) CFLAGS
+---------
+
+It's possible to alter the standard object C flags in the following way:
+
+  CFLAGS_perf.o += '...' - alters CFLAGS for perf.o object
+  CFLAGS_gtk += '...'    - alters CFLAGS for gtk build object
+
+This C flags changes has the scope of the Build makefile they are defined in.
+
+
+d) 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.
+
+
+e) 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