Design document for the unified scheme data
===========================================

How are things connected?
-------------------------

The unified scheme takes all its data from the build.info files seen
throughout the source tree.  These files hold the minimum information
needed to build end product files from diverse sources.  See the
section on build.info files below.

From the information in build.info files, Configure builds up an
information database as a hash table called %unified_info, which is
stored in configdata.pm, found at the top of the build tree (which may
or may not be the same as the source tree).

Configurations/common.tmpl uses the data from %unified_info to
generate the rules for building end product files as well as
intermediary files with the help of a few functions found in the
build-file templates.  See the section on build-file templates further
down for more information.

build.info files
----------------

As mentioned earlier, build.info files are meant to hold the minimum
information needed to build output files, and therefore only (with a
few possible exceptions [1]) have information about end products (such
as scripts, library files and programs) and source files (such as C
files, C header files, assembler files, etc).  Intermediate files such
as object files are rarely directly referred to in build.info files (and
when they are, it's always with the file name extension .o), they are
inferred by Configure.  By the same rule of minimalism, end product
file name extensions (such as .so, .a, .exe, etc) are never mentioned
in build.info.  Their file name extensions will be inferred by the
build-file templates, adapted for the platform they are meant for (see
sections on %unified_info and build-file templates further down).

The variables PROGRAMS, LIBS, ENGINES and SCRIPTS are used to declare
end products.  There are variants for them with '_NO_INST' as suffix
(PROGRAM_NO_INST etc) to specify end products that shouldn't get
installed.

The variables SOURCE, DEPEND and INCLUDE are indexed by a produced
file, and their values are the source used to produce that particular
produced file, extra dependencies, and include directories needed.

All their values in all the build.info throughout the source tree are
collected together and form a set of programs, libraries, engines and
scripts to be produced, source files, dependencies, etc etc etc.

Let's have a pretend example, a very limited contraption of OpenSSL,
composed of the program 'apps/openssl', the libraries 'libssl' and
'libcrypto', an engine 'engines/ossltest' and their sources and
dependencies.

    # build.info
    LIBS=libcrypto libssl
    INCLUDE[libcrypto]=include
    INCLUDE[libssl]=include
    DEPEND[libssl]=libcrypto

This is the top directory build.info file, and it tells us that two
libraries are to be built, the include directory 'include/' shall be
used throughout when building anything that will end up in each
library, and that the library 'libssl' depend on the library
'libcrypto' to function properly.

    # apps/build.info
    PROGRAMS=openssl
    SOURCE[openssl]=openssl.c
    INCLUDE[openssl]=.. ../include
    DEPEND[openssl]=../libssl

This is the build.info file in 'apps/', one may notice that all file
paths mentioned are relative to the directory the build.info file is
located in.  This one tells us that there's a program to be built
called 'apps/openssl' (the file name extension will depend on the
platform and is therefore not mentioned in the build.info file).  It's
built from one source file, 'apps/openssl.c', and building it requires
the use of '.' and 'include' include directories (both are declared
from the point of view of the 'apps/' directory), and that the program
depends on the library 'libssl' to function properly.

    # crypto/build.info
    LIBS=../libcrypto
    SOURCE[../libcrypto]=aes.c evp.c cversion.c
    DEPEND[cversion.o]=buildinf.h
    
    GENERATE[buildinf.h]=../util/mkbuildinf.pl "$(CC) $(CFLAGS)" "$(PLATFORM)"
    DEPEND[buildinf.h]=../Makefile
    DEPEND[../util/mkbuildinf.pl]=../util/Foo.pm

This is the build.info file in 'crypto', and it tells us a little more
about what's needed to produce 'libcrypto'.  LIBS is used again to
declare that 'libcrypto' is to be produced.  This declaration is
really unnecessary as it's already mentioned in the top build.info
file, but can make the info file easier to understand.  This is to
show that duplicate information isn't an issue.

This build.info file informs us that 'libcrypto' is built from a few
source files, 'crypto/aes.c', 'crypto/evp.c' and 'crypto/cversion.c'.
It also shows us that building the object file inferred from
'crypto/cversion.c' depends on 'crypto/buildinf.h'.  Finally, it 
also shows the possibility to declare how some files are generated
using some script, in this case a perl script, and how such scripts
can be declared to depend on other files, in this case a perl module.

Two things are worth an extra note:

'DEPEND[cversion.o]' mentions an object file.  DEPEND indexes is the
only location where it's valid to mention them

Lines in 'BEGINRAW'..'ENDRAW' sections must always mention files as
seen from the top directory, no exception.

    # ssl/build.info
    LIBS=../libssl
    SOURCE[../libssl]=tls.c

This is the build.info file in 'ssl/', and it tells us that the
library 'libssl' is built from the source file 'ssl/tls.c'.

    # engines/build.info
    ENGINES=dasync
    SOURCE[dasync]=e_dasync.c
    DEPEND[dasync]=../libcrypto
    INCLUDE[dasync]=../include

    ENGINES_NO_INST=ossltest
    SOURCE[ossltest]=e_ossltest.c
    DEPEND[ossltest]=../libcrypto.a
    INCLUDE[ossltest]=../include

This is the build.info file in 'engines/', telling us that two engines
called 'engines/dasync' and 'engines/ossltest' shall be built, that
dasync's source is 'engines/e_dasync.c' and ossltest's source is
'engines/e_ossltest.c' and that the include directory 'include/' may
be used when building anything that will be part of these engines.
Also, both engines depend on the library 'libcrypto' to function
properly.  ossltest is explicitly linked with the static variant of
the library 'libcrypto'.  Finally, only dasync is being installed, as
ossltest is only for internal testing.

When Configure digests these build.info files, the accumulated
information comes down to this:

    LIBS=libcrypto libssl
    SOURCE[libcrypto]=crypto/aes.c crypto/evp.c crypto/cversion.c
    DEPEND[crypto/cversion.o]=crypto/buildinf.h
    INCLUDE[libcrypto]=include
    SOURCE[libssl]=ssl/tls.c
    INCLUDE[libssl]=include
    DEPEND[libssl]=libcrypto
    
    PROGRAMS=apps/openssl
    SOURCE[apps/openssl]=apps/openssl.c
    INCLUDE[apps/openssl]=. include
    DEPEND[apps/openssl]=libssl

    ENGINES=engines/dasync
    SOURCE[engines/dasync]=engines/e_dasync.c
    DEPEND[engines/dasync]=libcrypto
    INCLUDE[engines/dasync]=include

    ENGINES_NO_INST=engines/ossltest
    SOURCE[engines/ossltest]=engines/e_ossltest.c
    DEPEND[engines/ossltest]=libcrypto.a
    INCLUDE[engines/ossltest]=include
    
    GENERATE[crypto/buildinf.h]=util/mkbuildinf.pl "$(CC) $(CFLAGS)" "$(PLATFORM)"
    DEPEND[crypto/buildinf.h]=Makefile
    DEPEND[util/mkbuildinf.pl]=util/Foo.pm


A few notes worth mentioning:

LIBS may be used to declare routine libraries only.

PROGRAMS may be used to declare programs only.

ENGINES may be used to declare engines only.

The indexes for SOURCE must only be end product files, such as
libraries, programs or engines.  The values of SOURCE variables must
only be source files (possibly generated).

INCLUDE and DEPEND shows a relationship between different files
(usually produced files) or between files and directories, such as a
program depending on a library, or between an object file and some
extra source file.

When Configure processes the build.info files, it will take it as
truth without question, and will therefore perform very few checks.
If the build tree is separate from the source tree, it will assume
that all built files and up in the build directory and that all source
files are to be found in the source tree, if they can be found there.
Configure will assume that source files that can't be found in the
source tree (such as 'crypto/bildinf.h' in the example above) are
generated and will be found in the build tree.


The %unified_info database
--------------------------

The information in all the build.info get digested by Configure and
collected into the %unified_info database, divided into the following
indexes:

  depends   => a hash table containing 'file' => [ 'dependency' ... ]
               pairs.  These are directly inferred from the DEPEND
               variables in build.info files.

  engines   => a list of engines.  These are directly inferred from
               the ENGINES variable in build.info files.

  generate  => a hash table containing 'file' => [ 'generator' ... ]
               pairs.  These are directly inferred from the GENERATE
               variables in build.info files.

  includes  => a hash table containing 'file' => [ 'include' ... ]
               pairs.  These are directly inferred from the INCLUDE
               variables in build.info files.

  install   => a hash table containing 'type' => [ 'file' ... ] pairs.
               The types are 'programs', 'libraries', 'engines' and
               'scripts', and the array of files list the files of
               that type that should be installed.

  libraries => a list of libraries.  These are directly inferred from
               the LIBS variable in build.info files.

  programs  => a list of programs.  These are directly inferred from
               the PROGRAMS variable in build.info files.

  rawlines  => a list of build-file lines.  These are a direct copy of
               the BEGINRAW..ENDRAW lines in build.info files.  Note:
               only the BEGINRAW..ENDRAW section for the current
               platform are copied, the rest are ignored.

  scripts   => a list of scripts.  There are directly inferred from
               the SCRIPTS variable in build.info files.

  sources   => a hash table containing 'file' => [ 'sourcefile' ... ]
               pairs.  These are indirectly inferred from the SOURCE
               variables in build.info files.  Object files are
               mentioned in this hash table, with source files from
               SOURCE variables, and AS source files for programs and
               libraries.

  shared_sources =>
               a hash table just like 'sources', but only as source
               files (object files) for building shared libraries.

As an example, here is how the build.info files example from the
section above would be digested into a %unified_info table:

    our %unified_info = (
        "depends" =>
            {
                "apps/openssl" =>
                    [
                        "libssl",
                    ],
                "crypto/buildinf.h" =>
                    [
                        "Makefile",
                    ],
                "crypto/cversion.o" =>
                    [
                        "crypto/buildinf.h",
                    ],
                "engines/dasync" =>
                    [
                        "libcrypto",
                    ],
                "engines/ossltest" =>
                    [
                        "libcrypto.a",
                    ],
                "libssl" =>
                    [
                        "libcrypto",
                    ],
                "util/mkbuildinf.pl" =>
                    [
                        "util/Foo.pm",
                    ],
            },
        "engines" =>
            [
                "engines/dasync",
                "engines/ossltest",
            ],
        "generate" =>
            {
                "crypto/buildinf.h" =>
                    [
                        "util/mkbuildinf.pl",
                        "\"\$(CC)",
                        "\$(CFLAGS)\"",
                        "\"$(PLATFORM)\"",
                    ],
            },
        "includes" =>
            {
                "apps/openssl" =>
                    [
                        ".",
                        "include",
                    ],
                "engines/ossltest" =>
                    [
                        "include"
                    ],
                "libcrypto" =>
                    [
                        "include",
                    ],
                "libssl" =>
                    [
                        "include",
                    ],
                "util/mkbuildinf.pl" =>
                    [
                        "util",
                    ],
            }
        "install" =>
            {
                "engines" =>
                    [
                        "engines/dasync",
                    ],
                "libraries" =>
                    [
                        "libcrypto",
                        "libssl",
                    ],
                "programs" =>
                    [
                        "apps/openssl",
                    ],
           },
        "libraries" =>
            [
                "libcrypto",
                "libssl",
            ],
        "programs" =>
            [
                "apps/openssl",
            ],
        "rawlines" =>
            [
            ],
        "sources" =>
            {
                "apps/openssl" =>
                    [
                        "apps/openssl.o",
                    ],
                "apps/openssl.o" =>
                    [
                        "apps/openssl.c",
                    ],
                "crypto/aes.o" =>
                    [
                        "crypto/aes.c",
                    ],
                "crypto/cversion.o" =>
                    [
                        "crypto/cversion.c",
                    ],
                "crypto/evp.o" =>
                    [
                        "crypto/evp.c",
                    ],
                "engines/e_dasync.o" =>
                    [
                        "engines/e_dasync.c",
                    ],
                "engines/dasync" =>
                    [
                        "engines/e_dasync.o",
                    ],
                "engines/e_ossltest.o" =>
                    [
                        "engines/e_ossltest.c",
                    ],
                "engines/ossltest" =>
                    [
                        "engines/e_ossltest.o",
                    ],
                "libcrypto" =>
                    [
                        "crypto/aes.c",
                        "crypto/cversion.c",
                        "crypto/evp.c",
                    ],
                "libssl" =>
                    [
                        "ssl/tls.c",
                    ],
                "ssl/tls.o" =>
                    [
                        "ssl/tls.c",
                    ],
            },
    );

As can be seen, everything in %unified_info is fairly simple suggest
of information.  Still, it tells us that to build all programs, we
must build 'apps/openssl', and to build the latter, we will need to
build all its sources ('apps/openssl.o' in this case) and all the
other things it depends on (such as 'libssl').  All those dependencies
need to be built as well, using the same logic, so to build 'libssl',
we need to build 'ssl/tls.o' as well as 'libcrypto', and to build the
latter...


Build-file templates
--------------------

Build-file templates are essentially build-files (such as Makefile on
Unix) with perl code fragments mixed in.  Those perl code fragment
will generate all the configuration dependent data, including all the
rules needed to build end product files and intermediary files alike.
At a minimum, there must be a perl code fragment that defines a set of
functions that are used to generates specific build-file rules, to
build static libraries from object files, to build shared libraries
from static libraries, to programs from object files and libraries,
etc.

    generatesrc - function that produces build file lines to generate
                  a source file from some input.

                  It's called like this:

                        generatesrc(src => "PATH/TO/tobegenerated",
                                    generator => [ "generatingfile", ... ]
                                    generator_incs => [ "INCL/PATH", ... ]
                                    generator_deps => [ "dep1", ... ]
                                    incs => [ "INCL/PATH", ... ],
                                    deps => [ "dep1", ... ],
                                    intent => one of "libs", "dso", "bin" );

                  'src' has the name of the file to be generated.
                  'generator' is the command or part of command to
                  generate the file, of which the first item is
                  expected to be the file to generate from.
                  generatesrc() is expected to analyse and figure out
                  exactly how to apply that file and how to capture
                  the result.  'generator_incs' and 'generator_deps'
                  are include directories and files that the generator
                  file itself depends on.  'incs' and 'deps' are
                  include directories and files that are used if $(CC)
                  is used as an intermediary step when generating the
                  end product (the file indicated by 'src').  'intent'
                  indicates what the generated file is going to be
                  used for.

    src2obj     - function that produces build file lines to build an
                  object file from source files and associated data.

                  It's called like this:

                        src2obj(obj => "PATH/TO/objectfile",
                                srcs => [ "PATH/TO/sourcefile", ... ],
                                deps => [ "dep1", ... ],
                                incs => [ "INCL/PATH", ... ]
                                intent => one of "lib", "dso", "bin" );

                  'obj' has the intended object file *without*
                  extension, src2obj() is expected to add that.
                  'srcs' has the list of source files to build the
                  object file, with the first item being the source
                  file that directly corresponds to the object file.
                  'deps' is a list of explicit dependencies.  'incs'
                  is a list of include file directories.  Finally,
                  'intent' indicates what this object file is going
                  to be used for.

    obj2lib     - function that produces build file lines to build a
                  static library file ("libfoo.a" in Unix terms) from
                  object files.

                  called like this:

                        obj2lib(lib => "PATH/TO/libfile",
                                objs => [ "PATH/TO/objectfile", ... ]);

                  'lib' has the intended library file name *without*
                  extension, obj2lib is expected to add that.  'objs'
                  has the list of object files (also *without*
                  extension) to build this library.

    libobj2shlib - function that produces build file lines to build a
                  shareable object library file ("libfoo.so" in Unix
                  terms) from the corresponding static library file
                  or object files.

                  called like this:

                        libobj2shlib(shlib => "PATH/TO/shlibfile",
                                     lib => "PATH/TO/libfile",
                                     objs => [ "PATH/TO/objectfile", ... ],
                                     deps => [ "PATH/TO/otherlibfile", ... ]);

                  'lib' has the intended library file name *without*
                  extension, libobj2shlib is expected to add that.
                  'shlib' has the corresponding shared library name
                  *without* extension.  'deps' has the list of other
                  libraries (also *without* extension) this library
                  needs to be linked with.  'objs' has the list of
                  object files (also *without* extension) to build
                  this library.

                  This function has a choice; it can use the
                  corresponding static library as input to make the
                  shared library, or the list of object files.

    obj2dynlib  - function that produces build file lines to build a
                  dynamically loadable library file ("libfoo.so" on
                  Unix) from object files.

                  called like this:

                        obj2dynlib(lib => "PATH/TO/libfile",
                                   objs => [ "PATH/TO/objectfile", ... ],
                                   deps => [ "PATH/TO/otherlibfile",
                                   ... ]);

                  This is almost the same as libobj2shlib, but the
                  intent is to build a shareable library that can be
                  loaded in runtime (a "plugin"...).  The differences
                  are subtle, one of the most visible ones is that the
                  resulting shareable library is produced from object
                  files only.

    obj2bin     - function that produces build file lines to build an
                  executable file from object files.

                  called like this:

                        obj2bin(bin => "PATH/TO/binfile",
                                objs => [ "PATH/TO/objectfile", ... ],
                                deps => [ "PATH/TO/libfile", ... ]);

                  'bin' has the intended executable file name
                  *without* extension, obj2bin is expected to add
                  that.  'objs' has the list of object files (also
                  *without* extension) to build this library.  'deps'
                  has the list of library files (also *without*
                  extension) that the programs needs to be linked
                  with.

    in2script   - function that produces build file lines to build a
                  script file from some input.

                  called like this:

                        in2script(script => "PATH/TO/scriptfile",
                                  sources => [ "PATH/TO/infile", ... ]);

                  'script' has the intended script file name.
                  'sources' has the list of source files to build the
                  resulting script from.

Along with the build-file templates is the driving engine
Configurations/common.tmpl, which looks through all the information in
%unified_info and generates all the rulesets to build libraries,
programs and all intermediate files, using the rule generating
functions defined in the build-file template.

As an example with the smaller build.info set we've seen as an
example, producing the rules to build 'libcrypto' would result in the
following calls:

    # Note: libobj2shlib will only be called if shared libraries are
    # to be produced.
    # Note 2: libobj2shlib gets both the name of the static library
    # and the names of all the object files that go into it.  It's up
    # to the implementation to decide which to use as input.
    # Note 3: common.tmpl peals off the ".o" extension from all object
    # files, as the platform at hand may have a different one.
    libobj2shlib(shlib => "libcrypto",
                 lib => "libcrypto",
                 objs => [ "crypto/aes", "crypto/evp", "crypto/cversion" ],
                 deps => [  ]);

    obj2lib(lib => "libcrypto"
            objs => [ "crypto/aes", "crypto/evp", "crypto/cversion" ]);

    src2obj(obj => "crypto/aes"
            srcs => [ "crypto/aes.c" ],
            deps => [ ],
            incs => [ "include" ],
            intent => "lib");

    src2obj(obj => "crypto/evp"
            srcs => [ "crypto/evp.c" ],
            deps => [ ],
            incs => [ "include" ],
            intent => "lib");

    src2obj(obj => "crypto/cversion"
            srcs => [ "crypto/cversion.c" ],
            deps => [ "crypto/buildinf.h" ],
            incs => [ "include" ],
            intent => "lib");

    generatesrc(src => "crypto/buildinf.h",
                generator => [ "util/mkbuildinf.pl", "\"$(CC)",
                               "$(CFLAGS)\"", "\"$(PLATFORM)\"" ],
                generator_incs => [ "util" ],
                generator_deps => [ "util/Foo.pm" ],
                incs => [ ],
                deps => [ ],
                intent => "lib");

The returned strings from all those calls are then concatenated
together and written to the resulting build-file.