Intro

=====

This directory contains a few sets of files that are used for

configuration in diverse ways:

    *.conf      Target platform configurations, please read

                'Configurations of OpenSSL target platforms' for more

                information.

    *.tmpl      Build file templates, please read 'Build-file

                programming with the "unified" build system' as well

                as 'Build info files' for more information.

    *.pm        Helper scripts / modules for the main `Configure`

                script.  See 'Configure helper scripts for more

                information.

Configurations of OpenSSL target platforms

==========================================

Configuration targets are a collection of facts that we know about

different platforms and their capabilities.  We organise them in a

hash table, where each entry represent a specific target.

Note that configuration target names must be unique across all config

files.  The Configure script does check that a config file doesn't

have config targets that shadow config targets from other files.

In each table entry, the following keys are significant:

        inherit_from    => Other targets to inherit values from.

                           Explained further below. [1]

        template        => Set to 1 if this isn't really a platform

                           target.  Instead, this target is a template

                           upon which other targets can be built.

                           Explained further below.  [1]

        sys_id          => System identity for systems where that

                           is difficult to determine automatically.

        enable          => Enable specific configuration features.

                           This MUST be an array of words.

        disable         => Disable specific configuration features.

                           This MUST be an array of words.

                           Note: if the same feature is both enabled

                           and disabled, disable wins.

        as              => The assembler command.  This is not always

                           used (for example on Unix, where the C

                           compiler is used instead).

        asflags         => Default assembler command flags [4].

        cpp             => The C preprocessor command, normally not

                           given, as the build file defaults are

                           usually good enough.

        cppflags        => Default C preprocessor flags [4].

        defines         => As an alternative, macro definitions may be

                           given here instead of in `cppflags' [4].

                           If given here, they MUST be as an array of

                           the string such as "MACRO=value", or just

                           "MACRO" for definitions without value.

        includes        => As an alternative, inclusion directories

                           may be given here instead of in `cppflags'

                           [4].  If given here, the MUST be an array

                           of strings, one directory specification

                           each.

        cc              => The C compiler command, usually one of "cc",

                           "gcc" or "clang".  This command is normally

                           also used to link object files and

                           libraries into the final program.

        cxx             => The C++ compiler command, usually one of

                           "c++", "g++" or "clang++".  This command is

                           also used when linking a program where at

                           least one of the object file is made from

                           C++ source.

        cflags          => Defaults C compiler flags [4].

        cxxflags        => Default  C++ compiler flags [4].  If unset,

                           it gets the same value as cflags.

        (linking is a complex thing, see [3] below)

        ld              => Linker command, usually not defined

                           (meaning the compiler command is used

                           instead).

                           (NOTE: this is here for future use, it's

                           not implemented yet)

        lflags          => Default flags used when linking apps,

                           shared libraries or DSOs [4].

        ex_libs         => Extra libraries that are needed when

                           linking shared libraries, DSOs or programs.

                           The value is also assigned to Libs.private

                           in $(libdir)/pkgconfig/libcrypto.pc.

        shared_cppflags => Extra C preprocessor flags used when

                           processing C files for shared libraries.

        shared_cflag    => Extra C compiler flags used when compiling

                           for shared libraries, typically something

                           like "-fPIC".

        shared_ldflag   => Extra linking flags used when linking

                           shared libraries.

        module_cppflags

        module_cflags

        module_ldflags  => Has the same function as the corresponding

                           `shared_' attributes, but for building DSOs.

                           When unset, they get the same values as the

                           corresponding `shared_' attributes.

        ar              => The library archive command, the default is

                           "ar".

                           (NOTE: this is here for future use, it's

                           not implemented yet)

        arflags         => Flags to be used with the library archive

                           command.  On Unix, this includes the

                           command letter, 'r' by default.

        ranlib          => The library archive indexing command, the

                           default is 'ranlib' it it exists.

        unistd          => An alternative header to the typical

                           '<unistd.h>'.  This is very rarely needed.

        shared_extension => File name extension used for shared

                            libraries.

        obj_extension   => File name extension used for object files.

                           On unix, this defaults to ".o" (NOTE: this

                           is here for future use, it's not

                           implemented yet)

        exe_extension   => File name extension used for executable

                           files.  On unix, this defaults to "" (NOTE:

                           this is here for future use, it's not

                           implemented yet)

        shlib_variant   => A "variant" identifier inserted between the base

                           shared library name and the extension.  On "unixy"

                           platforms (BSD, Linux, Solaris, MacOS/X, ...) this

                           supports installation of custom OpenSSL libraries

                           that don't conflict with other builds of OpenSSL

                           installed on the system.  The variant identifier

                           becomes part of the SONAME of the library and also

                           any symbol versions (symbol versions are not used or

                           needed with MacOS/X).  For example, on a system

                           where a default build would normally create the SSL

                           shared library as 'libssl.so -> libssl.so.1.1' with

                           the value of the symlink as the SONAME, a target

                           definition that sets 'shlib_variant => "-abc"' will

                           create 'libssl.so -> libssl-abc.so.1.1', again with

                           an SONAME equal to the value of the symlink.  The

                           symbol versions associated with the variant library

                           would then be 'OPENSSL_ABC_<version>' rather than

                           the default 'OPENSSL_<version>'. The string inserted

                           into symbol versions is obtained by mapping all

                           letters in the "variant" identifier to upper case

                           and all non-alphanumeric characters to '_'.

        thread_scheme   => The type of threads is used on the

                           configured platform.  Currently known

                           values are "(unknown)", "pthreads",

                           "uithreads" (a.k.a solaris threads) and

                           "winthreads".  Except for "(unknown)", the

                           actual value is currently ignored but may

                           be used in the future.  See further notes

                           below [2].

        dso_scheme      => The type of dynamic shared objects to build

                           for.  This mostly comes into play with

                           engines, but can be used for other purposes

                           as well.  Valid values are "DLFCN"

                           (dlopen() et al), "DLFCN_NO_H" (for systems

                           that use dlopen() et al but do not have

                           fcntl.h), "DL" (shl_load() et al), "WIN32"

                           and "VMS".

        perlasm_scheme  => The perlasm method used to create the

                           assembler files used when compiling with

                           assembler implementations.

        shared_target   => The shared library building method used.

                           This is a target found in Makefile.shared.

        build_scheme    => The scheme used to build up a Makefile.

                           In its simplest form, the value is a string

                           with the name of the build scheme.

                           The value may also take the form of a list

                           of strings, if the build_scheme is to have

                           some options.  In this case, the first

                           string in the list is the name of the build

                           scheme.

                           Currently recognised build scheme is "unified".

                           For the "unified" build scheme, this item

                           *must* be an array with the first being the

                           word "unified" and the second being a word

                           to identify the platform family.

        multilib        => On systems that support having multiple

                           implementations of a library (typically a

                           32-bit and a 64-bit variant), this is used

                           to have the different variants in different

                           directories.

        bn_ops          => Building options (was just bignum options in

                           the earlier history of this option, hence the

                           name). This is a string of words that describe

                           algorithms' implementation parameters that

                           are optimal for the designated target platform,

                           such as the type of integers used to build up

                           the bignum, different ways to implement certain

                           ciphers and so on. To fully comprehend the

                           meaning, the best is to read the affected

                           source.

                           The valid words are:

                           THIRTY_TWO_BIT       bignum limbs are 32 bits,

                                                this is default if no

                                                option is specified, it

                                                works on any supported

                                                system [unless "wider"

                                                limb size is implied in

                                                assembly code];

                           BN_LLONG             bignum limbs are 32 bits,

                                                but 64-bit 'unsigned long

                                                long' is used internally

                                                in calculations;

                           SIXTY_FOUR_BIT_LONG  bignum limbs are 64 bits

                                                and sizeof(long) is 8;

                           SIXTY_FOUR_BIT       bignums limbs are 64 bits,

                                                but execution environment

                                                is ILP32;

                           RC4_CHAR             RC4 key schedule is made

                                                up of 'unsigned char's;

                           RC4_INT              RC4 key schedule is made

                                                up of 'unsigned int's;

                           EXPORT_VAR_AS_FN     for shared libraries,

                                                export vars as

                                                accessor functions.

        apps_aux_src    => Extra source to build apps/openssl and other

                           apps, as needed by the target and that can be

                           collected in a library.

        apps_init_src   => Init source to build apps/openssl and other

                           apps, as needed by the target.  This code

                           cannot be placed in a library, as the rest

                           of the code isn't expected to link to it

                           explicitly.

        cpuid_asm_src   => assembler implementation of cpuid code as

                           well as OPENSSL_cleanse().

                           Default to mem_clr.c

        bn_asm_src      => Assembler implementation of core bignum

                           functions.

                           Defaults to bn_asm.c

        ec_asm_src      => Assembler implementation of core EC

                           functions.

        des_asm_src     => Assembler implementation of core DES

                           encryption functions.

                           Defaults to 'des_enc.c fcrypt_b.c'

        aes_asm_src     => Assembler implementation of core AES

                           functions.

                           Defaults to 'aes_core.c aes_cbc.c'

        bf_asm_src      => Assembler implementation of core BlowFish

                           functions.

                           Defaults to 'bf_enc.c'

        md5_asm_src     => Assembler implementation of core MD5

                           functions.

        sha1_asm_src    => Assembler implementation of core SHA1,

                           functions, and also possibly SHA256 and

                           SHA512 ones.

        cast_asm_src    => Assembler implementation of core CAST

                           functions.

                           Defaults to 'c_enc.c'

        rc4_asm_src     => Assembler implementation of core RC4

                           functions.

                           Defaults to 'rc4_enc.c rc4_skey.c'

        rmd160_asm_src  => Assembler implementation of core RMD160

                           functions.

        rc5_asm_src     => Assembler implementation of core RC5

                           functions.

                           Defaults to 'rc5_enc.c'

        wp_asm_src      => Assembler implementation of core WHIRLPOOL

                           functions.

        cmll_asm_src    => Assembler implementation of core CAMELLIA

                           functions.

                           Defaults to 'camellia.c cmll_misc.c cmll_cbc.c'

        modes_asm_src   => Assembler implementation of cipher modes,

                           currently the functions gcm_gmult_4bit and

                           gcm_ghash_4bit.

        padlock_asm_src => Assembler implementation of core parts of

                           the padlock engine.  This is mandatory on

                           any platform where the padlock engine might

                           actually be built.

[1] as part of the target configuration, one can have a key called

    'inherit_from' that indicate what other configurations to inherit

    data from.  These are resolved recursively.

    Inheritance works as a set of default values that can be overridden

    by corresponding key values in the inheriting configuration.

    Note 1: any configuration table can be used as a template.

    Note 2: pure templates have the attribute 'template => 1' and

            cannot be used as build targets.

    If several configurations are given in the 'inherit_from' array,

    the values of same attribute are concatenated with space

    separation.  With this, it's possible to have several smaller

    templates for different configuration aspects that can be combined

    into a complete configuration.

    instead of a scalar value or an array, a value can be a code block

    of the form 'sub { /* your code here */ }'.  This code block will

    be called with the list of inherited values for that key as

    arguments.  In fact, the concatenation of strings is really done

    by using 'sub { join(" ",@_) }' on the list of inherited values.

    An example:

        "foo" => {

                template => 1,

                haha => "ha ha",

                hoho => "ho",

                ignored => "This should not appear in the end result",

        },

        "bar" => {

                template => 1,

                haha => "ah",

                hoho => "haho",

                hehe => "hehe"

        },

        "laughter" => {

                inherit_from => [ "foo", "bar" ],

                hehe => sub { join(" ",(@_,"!!!")) },

                ignored => "",

        }

        The entry for "laughter" will become as follows after processing:

        "laughter" => {

                haha => "ha ha ah",

                hoho => "ho haho",

                hehe => "hehe !!!",

                ignored => ""

        }

[2] OpenSSL is built with threading capabilities unless the user

    specifies 'no-threads'.  The value of the key 'thread_scheme' may

    be "(unknown)", in which case the user MUST give some compilation

    flags to Configure.

[3] OpenSSL has three types of things to link from object files or

    static libraries:

    - shared libraries; that would be libcrypto and libssl.

    - shared objects (sometimes called dynamic libraries);  that would

      be the engines.

    - applications; those are apps/openssl and all the test apps.

    Very roughly speaking, linking is done like this (words in braces

    represent the configuration settings documented at the beginning

    of this file):

    shared libraries:

        {ld} $(CFLAGS) {lflags} {shared_ldflag} -o libfoo.so \

            foo/something.o foo/somethingelse.o {ex_libs}

    shared objects:

        {ld} $(CFLAGS) {lflags} {module_ldflags} -o libeng.so \

            blah1.o blah2.o -lcrypto {ex_libs}

    applications:

        {ld} $(CFLAGS) {lflags} -o app \

            app1.o utils.o -lssl -lcrypto {ex_libs}

[4] There are variants of these attribute, prefixed with `lib_',

    `dso_' or `bin_'.  Those variants replace the unprefixed attribute

    when building library, DSO or program modules specifically.

Historically, the target configurations came in form of a string with

values separated by colons.  This use is deprecated.  The string form

looked like this:

   "target" => "{cc}:{cflags}:{unistd}:{thread_cflag}:{sys_id}:{lflags}:{bn_ops}:{cpuid_obj}:{bn_obj}:{ec_obj}:{des_obj}:{aes_obj}:{bf_obj}:{md5_obj}:{sha1_obj}:{cast_obj}:{rc4_obj}:{rmd160_obj}:{rc5_obj}:{wp_obj}:{cmll_obj}:{modes_obj}:{padlock_obj}:{perlasm_scheme}:{dso_scheme}:{shared_target}:{shared_cflag}:{shared_ldflag}:{shared_extension}:{ranlib}:{arflags}:{multilib}"

Build info files

================

The build.info files that are spread over the source tree contain the

minimum information needed to build and distribute OpenSSL.  It uses a

simple and yet fairly powerful language to determine what needs to be

built, from what sources, and other relationships between files.

For every build.info file, all file references are relative to the

directory of the build.info file for source files, and the

corresponding build directory for built files if the build tree

differs from the source tree.

When processed, every line is processed with the perl module

Text::Template, using the delimiters "{-" and "-}".  The hashes

%config and %target are passed to the perl fragments, along with

$sourcedir and $builddir, which are the locations of the source

directory for the current build.info file and the corresponding build

directory, all relative to the top of the build tree.

To begin with, things to be built are declared by setting specific

variables:

    PROGRAMS=foo bar

    LIBS=libsomething

    ENGINES=libeng

    SCRIPTS=myhack

    EXTRA=file1 file2

Note that the files mentioned for PROGRAMS, LIBS and ENGINES *must* be

without extensions.  The build file templates will figure them out.

For each thing to be built, it is then possible to say what sources

they are built from:

    PROGRAMS=foo bar

    SOURCE[foo]=foo.c common.c

    SOURCE[bar]=bar.c extra.c common.c

It's also possible to tell some other dependencies:

    DEPEND[foo]=libsomething

    DEPEND[libbar]=libsomethingelse

(it could be argued that 'libsomething' and 'libsomethingelse' are

source as well.  However, the files given through SOURCE are expected

to be located in the source tree while files given through DEPEND are

expected to be located in the build tree)

It's also possible to depend on static libraries explicitly:

    DEPEND[foo]=libsomething.a

    DEPEND[libbar]=libsomethingelse.a

This should be rarely used, and care should be taken to make sure it's

only used when supported.  For example, native Windows build doesn't

support building static libraries and DLLs at the same time, so using

static libraries on Windows can only be done when configured

'no-shared'.

One some platforms, shared libraries come with a name that's different

from their static counterpart.  That's declared as follows:

    SHARED_NAME[libfoo]=cygfoo-{- $config{shlibver} -}

The example is from Cygwin, which has a required naming convention.

Sometimes, it makes sense to rename an output file, for example a

library:

    RENAME[libfoo]=libbar

That line has "libfoo" renamed to "libbar".  While it makes no

sense at all to just have a rename like that (why not just use

"libbar" everywhere?), it does make sense when it can be used

conditionally.  See a little further below for an example.

In some cases, it's desirable to include some source files in the

shared form of a library only:

    SHARED_SOURCE[libfoo]=dllmain.c

For any file to be built, it's also possible to tell what extra

include paths the build of their source files should use:

    INCLUDE[foo]=include

In some cases, one might want to generate some source files from

others, that's done as follows:

    GENERATE[foo.s]=asm/something.pl $(CFLAGS)

    GENERATE[bar.s]=asm/bar.S

The value of each GENERATE line is a command line or part of it.

Configure places no rules on the command line, except that the first

item must be the generator file.  It is, however, entirely up to the

build file template to define exactly how those command lines should

be handled, how the output is captured and so on.

Sometimes, the generator file itself depends on other files, for

example if it is a perl script that depends on other perl modules.

This can be expressed using DEPEND like this:

    DEPEND[asm/something.pl]=../perlasm/Foo.pm

There may also be cases where the exact file isn't easily specified,

but an inclusion directory still needs to be specified.  INCLUDE can

be used in that case:

    INCLUDE[asm/something.pl]=../perlasm

NOTE: GENERATE lines are limited to one command only per GENERATE.

As a last resort, it's possible to have raw build file lines, between

BEGINRAW and ENDRAW lines as follows:

    BEGINRAW[Makefile(unix)]

    haha.h: {- $builddir -}/Makefile

        echo "/* haha */" > haha.h

    ENDRAW[Makefile(unix)]

The word within square brackets is the build_file configuration item

or the build_file configuration item followed by the second word in the

build_scheme configuration item for the configured target within

parenthesis as shown above.  For example, with the following relevant

configuration items:

   build_file   => "build.ninja"

   build_scheme => [ "unified", "unix" ]

... these lines will be considered:

   BEGINRAW[build.ninja]

   build haha.h: echo "/* haha */" > haha.h

   ENDRAW[build.ninja]

   BEGINRAW[build.ninja(unix)]

   build hoho.h: echo "/* hoho */" > hoho.h

   ENDRAW[build.ninja(unix)]

Should it be needed because the recipes within a RAW section might

clash with those generated by Configure, it's possible to tell it

not to generate them with the use of OVERRIDES, for example:

    SOURCE[libfoo]=foo.c bar.c

    OVERRIDES=bar.o

    BEGINRAW[Makefile(unix)]

    bar.o: bar.c

    	$(CC) $(CFLAGS) -DSPECIAL -c -o $@ $<

    ENDRAW[Makefile(unix)]

See the documentation further up for more information on configuration

items.

Finally, you can have some simple conditional use of the build.info

information, looking like this:

    IF[1]

     something

    ELSIF[2]

     something other

    ELSE

     something else

    ENDIF

The expression in square brackets is interpreted as a string in perl,

and will be seen as true if perl thinks it is, otherwise false.  For

example, the above would have "something" used, since 1 is true.

Together with the use of Text::Template, this can be used as

conditions based on something in the passed variables, for example:

    IF[{- $disabled{shared} -}]

      LIBS=libcrypto

      SOURCE[libcrypto]=...

    ELSE

      LIBS=libfoo

      SOURCE[libfoo]=...

    ENDIF

or:

    # VMS has a cultural standard where all libraries are prefixed.

    # For OpenSSL, the choice is 'ossl_'

    IF[{- $config{target} =~ /^vms/ -}]

     RENAME[libcrypto]=ossl_libcrypto

     RENAME[libssl]=ossl_libssl

    ENDIF

Build-file programming with the "unified" build system

======================================================

"Build files" are called "Makefile" on Unix-like operating systems,

"descrip.mms" for MMS on VMS, "makefile" for nmake on Windows, etc.

To use the "unified" build system, the target configuration needs to

set the three items 'build_scheme', 'build_file' and 'build_command'.

In the rest of this section, we will assume that 'build_scheme' is set

to "unified" (see the configurations documentation above for the

details).

For any name given by 'build_file', the "unified" system expects a

template file in Configurations/ named like the build file, with

".tmpl" appended, or in case of possible ambiguity, a combination of

the second 'build_scheme' list item and the 'build_file' name.  For

example, if 'build_file' is set to "Makefile", the template could be

Configurations/Makefile.tmpl or Configurations/unix-Makefile.tmpl.

In case both Configurations/unix-Makefile.tmpl and

Configurations/Makefile.tmpl are present, the former takes

precedence.

The build-file template is processed with the perl module

Text::Template, using "{-" and "-}" as delimiters that enclose the

perl code fragments that generate configuration-dependent content.

Those perl fragments have access to all the hash variables from

configdata.pem.

The build-file template is expected to define at least the following

perl functions in a perl code fragment enclosed with "{-" and "-}".

They are all expected to return a string with the lines they produce.

    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", ... ]

                                    generator => [ "generatingfile", ... ]

                                    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.

    obj2dso     - function that produces build file lines to build a

                  dynamic shared object file from object files.

                  called like this:

                        obj2dso(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.

In all cases, file file paths are relative to the build tree top, and

the build file actions run with the build tree top as current working

directory.

Make sure to end the section with these functions with a string that

you thing is appropriate for the resulting build file.  If nothing

else, end it like this:

      "";       # Make sure no lingering values end up in the Makefile

    -}

Configure helper scripts

========================

Configure uses helper scripts in this directory:

Checker scripts

---------------

These scripts are per platform family, to check the integrity of the

tools used for configuration and building.  The checker script used is

either {build_platform}-{build_file}-checker.pm or

{build_platform}-checker.pm, where {build_platform} is the second

'build_scheme' list element from the configuration target data, and

{build_file} is 'build_file' from the same target data.

If the check succeeds, the script is expected to end with a non-zero

expression.  If the check fails, the script can end with a zero, or

with a `die`.