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    1 Intro
    2 =====
    3 
    4 This directory contains a few sets of files that are used for
    5 configuration in diverse ways:
    6 
    7     *.conf      Target platform configurations, please read
    8                 'Configurations of OpenSSL target platforms' for more
    9                 information.
   10     *.tmpl      Build file templates, please read 'Build-file
   11                 programming with the "unified" build system' as well
   12                 as 'Build info files' for more information.
   13     *.pm        Helper scripts / modules for the main `Configure`
   14                 script.  See 'Configure helper scripts for more
   15                 information.
   16 
   17 
   18 Configurations of OpenSSL target platforms
   19 ==========================================
   20 
   21 Configuration targets are a collection of facts that we know about
   22 different platforms and their capabilities.  We organise them in a
   23 hash table, where each entry represent a specific target.
   24 
   25 Note that configuration target names must be unique across all config
   26 files.  The Configure script does check that a config file doesn't
   27 have config targets that shadow config targets from other files.
   28 
   29 In each table entry, the following keys are significant:
   30 
   31         inherit_from    => Other targets to inherit values from.
   32                            Explained further below. [1]
   33         template        => Set to 1 if this isn't really a platform
   34                            target.  Instead, this target is a template
   35                            upon which other targets can be built.
   36                            Explained further below.  [1]
   37 
   38         sys_id          => System identity for systems where that
   39                            is difficult to determine automatically.
   40 
   41         enable          => Enable specific configuration features.
   42                            This MUST be an array of words.
   43         disable         => Disable specific configuration features.
   44                            This MUST be an array of words.
   45                            Note: if the same feature is both enabled
   46                            and disabled, disable wins.
   47 
   48         as              => The assembler command.  This is not always
   49                            used (for example on Unix, where the C
   50                            compiler is used instead).
   51         asflags         => Default assembler command flags [4].
   52         cpp             => The C preprocessor command, normally not
   53                            given, as the build file defaults are
   54                            usually good enough.
   55         cppflags        => Default C preprocessor flags [4].
   56         defines         => As an alternative, macro definitions may be
   57                            given here instead of in `cppflags' [4].
   58                            If given here, they MUST be as an array of
   59                            the string such as "MACRO=value", or just
   60                            "MACRO" for definitions without value.
   61         includes        => As an alternative, inclusion directories
   62                            may be given here instead of in `cppflags'
   63                            [4].  If given here, the MUST be an array
   64                            of strings, one directory specification
   65                            each.
   66         cc              => The C compiler command, usually one of "cc",
   67                            "gcc" or "clang".  This command is normally
   68                            also used to link object files and
   69                            libraries into the final program.
   70         cxx             => The C++ compiler command, usually one of
   71                            "c++", "g++" or "clang++".  This command is
   72                            also used when linking a program where at
   73                            least one of the object file is made from
   74                            C++ source.
   75         cflags          => Defaults C compiler flags [4].
   76         cxxflags        => Default  C++ compiler flags [4].  If unset,
   77                            it gets the same value as cflags.
   78 
   79         (linking is a complex thing, see [3] below)
   80         ld              => Linker command, usually not defined
   81                            (meaning the compiler command is used
   82                            instead).
   83                            (NOTE: this is here for future use, it's
   84                            not implemented yet)
   85         lflags          => Default flags used when linking apps,
   86                            shared libraries or DSOs [4].
   87         ex_libs         => Extra libraries that are needed when
   88                            linking shared libraries, DSOs or programs.
   89                            The value is also assigned to Libs.private
   90                            in $(libdir)/pkgconfig/libcrypto.pc.
   91 
   92         shared_cppflags => Extra C preprocessor flags used when
   93                            processing C files for shared libraries.
   94         shared_cflag    => Extra C compiler flags used when compiling
   95                            for shared libraries, typically something
   96                            like "-fPIC".
   97         shared_ldflag   => Extra linking flags used when linking
   98                            shared libraries.
   99         module_cppflags
  100         module_cflags
  101         module_ldflags  => Has the same function as the corresponding
  102                            `shared_' attributes, but for building DSOs.
  103                            When unset, they get the same values as the
  104                            corresponding `shared_' attributes.
  105 
  106         ar              => The library archive command, the default is
  107                            "ar".
  108                            (NOTE: this is here for future use, it's
  109                            not implemented yet)
  110         arflags         => Flags to be used with the library archive
  111                            command.  On Unix, this includes the
  112                            command letter, 'r' by default.
  113 
  114         ranlib          => The library archive indexing command, the
  115                            default is 'ranlib' it it exists.
  116 
  117         unistd          => An alternative header to the typical
  118                            '<unistd.h>'.  This is very rarely needed.
  119 
  120         shared_extension => File name extension used for shared
  121                             libraries.
  122         obj_extension   => File name extension used for object files.
  123                            On unix, this defaults to ".o" (NOTE: this
  124                            is here for future use, it's not
  125                            implemented yet)
  126         exe_extension   => File name extension used for executable
  127                            files.  On unix, this defaults to "" (NOTE:
  128                            this is here for future use, it's not
  129                            implemented yet)
  130         shlib_variant   => A "variant" identifier inserted between the base
  131                            shared library name and the extension.  On "unixy"
  132                            platforms (BSD, Linux, Solaris, MacOS/X, ...) this
  133                            supports installation of custom OpenSSL libraries
  134                            that don't conflict with other builds of OpenSSL
  135                            installed on the system.  The variant identifier
  136                            becomes part of the SONAME of the library and also
  137                            any symbol versions (symbol versions are not used or
  138                            needed with MacOS/X).  For example, on a system
  139                            where a default build would normally create the SSL
  140                            shared library as 'libssl.so -> libssl.so.1.1' with
  141                            the value of the symlink as the SONAME, a target
  142                            definition that sets 'shlib_variant => "-abc"' will
  143                            create 'libssl.so -> libssl-abc.so.1.1', again with
  144                            an SONAME equal to the value of the symlink.  The
  145                            symbol versions associated with the variant library
  146                            would then be 'OPENSSL_ABC_<version>' rather than
  147                            the default 'OPENSSL_<version>'. The string inserted
  148                            into symbol versions is obtained by mapping all
  149                            letters in the "variant" identifier to upper case
  150                            and all non-alphanumeric characters to '_'.
  151 
  152         thread_scheme   => The type of threads is used on the
  153                            configured platform.  Currently known
  154                            values are "(unknown)", "pthreads",
  155                            "uithreads" (a.k.a solaris threads) and
  156                            "winthreads".  Except for "(unknown)", the
  157                            actual value is currently ignored but may
  158                            be used in the future.  See further notes
  159                            below [2].
  160         dso_scheme      => The type of dynamic shared objects to build
  161                            for.  This mostly comes into play with
  162                            engines, but can be used for other purposes
  163                            as well.  Valid values are "DLFCN"
  164                            (dlopen() et al), "DLFCN_NO_H" (for systems
  165                            that use dlopen() et al but do not have
  166                            fcntl.h), "DL" (shl_load() et al), "WIN32"
  167                            and "VMS".
  168         perlasm_scheme  => The perlasm method used to create the
  169                            assembler files used when compiling with
  170                            assembler implementations.
  171         shared_target   => The shared library building method used.
  172                            This is a target found in Makefile.shared.
  173         build_scheme    => The scheme used to build up a Makefile.
  174                            In its simplest form, the value is a string
  175                            with the name of the build scheme.
  176                            The value may also take the form of a list
  177                            of strings, if the build_scheme is to have
  178                            some options.  In this case, the first
  179                            string in the list is the name of the build
  180                            scheme.
  181                            Currently recognised build scheme is "unified".
  182                            For the "unified" build scheme, this item
  183                            *must* be an array with the first being the
  184                            word "unified" and the second being a word
  185                            to identify the platform family.
  186 
  187         multilib        => On systems that support having multiple
  188                            implementations of a library (typically a
  189                            32-bit and a 64-bit variant), this is used
  190                            to have the different variants in different
  191                            directories.
  192 
  193         bn_ops          => Building options (was just bignum options in
  194                            the earlier history of this option, hence the
  195                            name). This is a string of words that describe
  196                            algorithms' implementation parameters that
  197                            are optimal for the designated target platform,
  198                            such as the type of integers used to build up
  199                            the bignum, different ways to implement certain
  200                            ciphers and so on. To fully comprehend the
  201                            meaning, the best is to read the affected
  202                            source.
  203                            The valid words are:
  204 
  205                            THIRTY_TWO_BIT       bignum limbs are 32 bits,
  206                                                 this is default if no
  207                                                 option is specified, it
  208                                                 works on any supported
  209                                                 system [unless "wider"
  210                                                 limb size is implied in
  211                                                 assembly code];
  212                            BN_LLONG             bignum limbs are 32 bits,
  213                                                 but 64-bit 'unsigned long
  214                                                 long' is used internally
  215                                                 in calculations;
  216                            SIXTY_FOUR_BIT_LONG  bignum limbs are 64 bits
  217                                                 and sizeof(long) is 8;
  218                            SIXTY_FOUR_BIT       bignums limbs are 64 bits,
  219                                                 but execution environment
  220                                                 is ILP32;
  221                            RC4_CHAR             RC4 key schedule is made
  222                                                 up of 'unsigned char's;
  223                            RC4_INT              RC4 key schedule is made
  224                                                 up of 'unsigned int's;
  225                            EXPORT_VAR_AS_FN     for shared libraries,
  226                                                 export vars as
  227                                                 accessor functions.
  228 
  229         apps_aux_src    => Extra source to build apps/openssl and other
  230                            apps, as needed by the target and that can be
  231                            collected in a library.
  232         apps_init_src   => Init source to build apps/openssl and other
  233                            apps, as needed by the target.  This code
  234                            cannot be placed in a library, as the rest
  235                            of the code isn't expected to link to it
  236                            explicitly.
  237         cpuid_asm_src   => assembler implementation of cpuid code as
  238                            well as OPENSSL_cleanse().
  239                            Default to mem_clr.c
  240         bn_asm_src      => Assembler implementation of core bignum
  241                            functions.
  242                            Defaults to bn_asm.c
  243         ec_asm_src      => Assembler implementation of core EC
  244                            functions.
  245         des_asm_src     => Assembler implementation of core DES
  246                            encryption functions.
  247                            Defaults to 'des_enc.c fcrypt_b.c'
  248         aes_asm_src     => Assembler implementation of core AES
  249                            functions.
  250                            Defaults to 'aes_core.c aes_cbc.c'
  251         bf_asm_src      => Assembler implementation of core BlowFish
  252                            functions.
  253                            Defaults to 'bf_enc.c'
  254         md5_asm_src     => Assembler implementation of core MD5
  255                            functions.
  256         sha1_asm_src    => Assembler implementation of core SHA1,
  257                            functions, and also possibly SHA256 and
  258                            SHA512 ones.
  259         cast_asm_src    => Assembler implementation of core CAST
  260                            functions.
  261                            Defaults to 'c_enc.c'
  262         rc4_asm_src     => Assembler implementation of core RC4
  263                            functions.
  264                            Defaults to 'rc4_enc.c rc4_skey.c'
  265         rmd160_asm_src  => Assembler implementation of core RMD160
  266                            functions.
  267         rc5_asm_src     => Assembler implementation of core RC5
  268                            functions.
  269                            Defaults to 'rc5_enc.c'
  270         wp_asm_src      => Assembler implementation of core WHIRLPOOL
  271                            functions.
  272         cmll_asm_src    => Assembler implementation of core CAMELLIA
  273                            functions.
  274                            Defaults to 'camellia.c cmll_misc.c cmll_cbc.c'
  275         modes_asm_src   => Assembler implementation of cipher modes,
  276                            currently the functions gcm_gmult_4bit and
  277                            gcm_ghash_4bit.
  278         padlock_asm_src => Assembler implementation of core parts of
  279                            the padlock engine.  This is mandatory on
  280                            any platform where the padlock engine might
  281                            actually be built.
  282 
  283 
  284 [1] as part of the target configuration, one can have a key called
  285     'inherit_from' that indicate what other configurations to inherit
  286     data from.  These are resolved recursively.
  287 
  288     Inheritance works as a set of default values that can be overridden
  289     by corresponding key values in the inheriting configuration.
  290 
  291     Note 1: any configuration table can be used as a template.
  292     Note 2: pure templates have the attribute 'template => 1' and
  293             cannot be used as build targets.
  294 
  295     If several configurations are given in the 'inherit_from' array,
  296     the values of same attribute are concatenated with space
  297     separation.  With this, it's possible to have several smaller
  298     templates for different configuration aspects that can be combined
  299     into a complete configuration.
  300 
  301     instead of a scalar value or an array, a value can be a code block
  302     of the form 'sub { /* your code here */ }'.  This code block will
  303     be called with the list of inherited values for that key as
  304     arguments.  In fact, the concatenation of strings is really done
  305     by using 'sub { join(" ",@_) }' on the list of inherited values.
  306 
  307     An example:
  308 
  309         "foo" => {
  310                 template => 1,
  311                 haha => "ha ha",
  312                 hoho => "ho",
  313                 ignored => "This should not appear in the end result",
  314         },
  315         "bar" => {
  316                 template => 1,
  317                 haha => "ah",
  318                 hoho => "haho",
  319                 hehe => "hehe"
  320         },
  321         "laughter" => {
  322                 inherit_from => [ "foo", "bar" ],
  323                 hehe => sub { join(" ",(@_,"!!!")) },
  324                 ignored => "",
  325         }
  326 
  327         The entry for "laughter" will become as follows after processing:
  328 
  329         "laughter" => {
  330                 haha => "ha ha ah",
  331                 hoho => "ho haho",
  332                 hehe => "hehe !!!",
  333                 ignored => ""
  334         }
  335 
  336 [2] OpenSSL is built with threading capabilities unless the user
  337     specifies 'no-threads'.  The value of the key 'thread_scheme' may
  338     be "(unknown)", in which case the user MUST give some compilation
  339     flags to Configure.
  340 
  341 [3] OpenSSL has three types of things to link from object files or
  342     static libraries:
  343 
  344     - shared libraries; that would be libcrypto and libssl.
  345     - shared objects (sometimes called dynamic libraries);  that would
  346       be the engines.
  347     - applications; those are apps/openssl and all the test apps.
  348 
  349     Very roughly speaking, linking is done like this (words in braces
  350     represent the configuration settings documented at the beginning
  351     of this file):
  352 
  353     shared libraries:
  354         {ld} $(CFLAGS) {lflags} {shared_ldflag} -o libfoo.so \
  355             foo/something.o foo/somethingelse.o {ex_libs}
  356 
  357     shared objects:
  358         {ld} $(CFLAGS) {lflags} {module_ldflags} -o libeng.so \
  359             blah1.o blah2.o -lcrypto {ex_libs}
  360 
  361     applications:
  362         {ld} $(CFLAGS) {lflags} -o app \
  363             app1.o utils.o -lssl -lcrypto {ex_libs}
  364 
  365 [4] There are variants of these attribute, prefixed with `lib_',
  366     `dso_' or `bin_'.  Those variants replace the unprefixed attribute
  367     when building library, DSO or program modules specifically.
  368 
  369 Historically, the target configurations came in form of a string with
  370 values separated by colons.  This use is deprecated.  The string form
  371 looked like this:
  372 
  373    "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}"
  374 
  375 
  376 Build info files
  377 ================
  378 
  379 The build.info files that are spread over the source tree contain the
  380 minimum information needed to build and distribute OpenSSL.  It uses a
  381 simple and yet fairly powerful language to determine what needs to be
  382 built, from what sources, and other relationships between files.
  383 
  384 For every build.info file, all file references are relative to the
  385 directory of the build.info file for source files, and the
  386 corresponding build directory for built files if the build tree
  387 differs from the source tree.
  388 
  389 When processed, every line is processed with the perl module
  390 Text::Template, using the delimiters "{-" and "-}".  The hashes
  391 %config and %target are passed to the perl fragments, along with
  392 $sourcedir and $builddir, which are the locations of the source
  393 directory for the current build.info file and the corresponding build
  394 directory, all relative to the top of the build tree.
  395 
  396 To begin with, things to be built are declared by setting specific
  397 variables:
  398 
  399     PROGRAMS=foo bar
  400     LIBS=libsomething
  401     ENGINES=libeng
  402     SCRIPTS=myhack
  403     EXTRA=file1 file2
  404 
  405 Note that the files mentioned for PROGRAMS, LIBS and ENGINES *must* be
  406 without extensions.  The build file templates will figure them out.
  407 
  408 For each thing to be built, it is then possible to say what sources
  409 they are built from:
  410 
  411     PROGRAMS=foo bar
  412     SOURCE[foo]=foo.c common.c
  413     SOURCE[bar]=bar.c extra.c common.c
  414 
  415 It's also possible to tell some other dependencies:
  416 
  417     DEPEND[foo]=libsomething
  418     DEPEND[libbar]=libsomethingelse
  419 
  420 (it could be argued that 'libsomething' and 'libsomethingelse' are
  421 source as well.  However, the files given through SOURCE are expected
  422 to be located in the source tree while files given through DEPEND are
  423 expected to be located in the build tree)
  424 
  425 It's also possible to depend on static libraries explicitly:
  426 
  427     DEPEND[foo]=libsomething.a
  428     DEPEND[libbar]=libsomethingelse.a
  429 
  430 This should be rarely used, and care should be taken to make sure it's
  431 only used when supported.  For example, native Windows build doesn't
  432 support building static libraries and DLLs at the same time, so using
  433 static libraries on Windows can only be done when configured
  434 'no-shared'.
  435 
  436 One some platforms, shared libraries come with a name that's different
  437 from their static counterpart.  That's declared as follows:
  438 
  439     SHARED_NAME[libfoo]=cygfoo-{- $config{shlibver} -}
  440 
  441 The example is from Cygwin, which has a required naming convention.
  442 
  443 Sometimes, it makes sense to rename an output file, for example a
  444 library:
  445 
  446     RENAME[libfoo]=libbar
  447 
  448 That line has "libfoo" renamed to "libbar".  While it makes no
  449 sense at all to just have a rename like that (why not just use
  450 "libbar" everywhere?), it does make sense when it can be used
  451 conditionally.  See a little further below for an example.
  452 
  453 In some cases, it's desirable to include some source files in the
  454 shared form of a library only:
  455 
  456     SHARED_SOURCE[libfoo]=dllmain.c
  457 
  458 For any file to be built, it's also possible to tell what extra
  459 include paths the build of their source files should use:
  460 
  461     INCLUDE[foo]=include
  462 
  463 In some cases, one might want to generate some source files from
  464 others, that's done as follows:
  465 
  466     GENERATE[foo.s]=asm/something.pl $(CFLAGS)
  467     GENERATE[bar.s]=asm/bar.S
  468 
  469 The value of each GENERATE line is a command line or part of it.
  470 Configure places no rules on the command line, except that the first
  471 item must be the generator file.  It is, however, entirely up to the
  472 build file template to define exactly how those command lines should
  473 be handled, how the output is captured and so on.
  474 
  475 Sometimes, the generator file itself depends on other files, for
  476 example if it is a perl script that depends on other perl modules.
  477 This can be expressed using DEPEND like this:
  478 
  479     DEPEND[asm/something.pl]=../perlasm/Foo.pm
  480 
  481 There may also be cases where the exact file isn't easily specified,
  482 but an inclusion directory still needs to be specified.  INCLUDE can
  483 be used in that case:
  484 
  485     INCLUDE[asm/something.pl]=../perlasm
  486 
  487 NOTE: GENERATE lines are limited to one command only per GENERATE.
  488 
  489 As a last resort, it's possible to have raw build file lines, between
  490 BEGINRAW and ENDRAW lines as follows:
  491 
  492     BEGINRAW[Makefile(unix)]
  493     haha.h: {- $builddir -}/Makefile
  494         echo "/* haha */" > haha.h
  495     ENDRAW[Makefile(unix)]
  496 
  497 The word within square brackets is the build_file configuration item
  498 or the build_file configuration item followed by the second word in the
  499 build_scheme configuration item for the configured target within
  500 parenthesis as shown above.  For example, with the following relevant
  501 configuration items:
  502 
  503    build_file   => "build.ninja"
  504    build_scheme => [ "unified", "unix" ]
  505 
  506 ... these lines will be considered:
  507 
  508    BEGINRAW[build.ninja]
  509    build haha.h: echo "/* haha */" > haha.h
  510    ENDRAW[build.ninja]
  511 
  512    BEGINRAW[build.ninja(unix)]
  513    build hoho.h: echo "/* hoho */" > hoho.h
  514    ENDRAW[build.ninja(unix)]
  515 
  516 Should it be needed because the recipes within a RAW section might
  517 clash with those generated by Configure, it's possible to tell it
  518 not to generate them with the use of OVERRIDES, for example:
  519 
  520     SOURCE[libfoo]=foo.c bar.c
  521 
  522     OVERRIDES=bar.o
  523     BEGINRAW[Makefile(unix)]
  524     bar.o: bar.c
  525     	$(CC) $(CFLAGS) -DSPECIAL -c -o $@ $<
  526     ENDRAW[Makefile(unix)]
  527 
  528 See the documentation further up for more information on configuration
  529 items.
  530 
  531 Finally, you can have some simple conditional use of the build.info
  532 information, looking like this:
  533 
  534     IF[1]
  535      something
  536     ELSIF[2]
  537      something other
  538     ELSE
  539      something else
  540     ENDIF
  541 
  542 The expression in square brackets is interpreted as a string in perl,
  543 and will be seen as true if perl thinks it is, otherwise false.  For
  544 example, the above would have "something" used, since 1 is true.
  545 
  546 Together with the use of Text::Template, this can be used as
  547 conditions based on something in the passed variables, for example:
  548 
  549     IF[{- $disabled{shared} -}]
  550       LIBS=libcrypto
  551       SOURCE[libcrypto]=...
  552     ELSE
  553       LIBS=libfoo
  554       SOURCE[libfoo]=...
  555     ENDIF
  556 
  557 or:
  558 
  559     # VMS has a cultural standard where all libraries are prefixed.
  560     # For OpenSSL, the choice is 'ossl_'
  561     IF[{- $config{target} =~ /^vms/ -}]
  562      RENAME[libcrypto]=ossl_libcrypto
  563      RENAME[libssl]=ossl_libssl
  564     ENDIF
  565 
  566 
  567 Build-file programming with the "unified" build system
  568 ======================================================
  569 
  570 "Build files" are called "Makefile" on Unix-like operating systems,
  571 "descrip.mms" for MMS on VMS, "makefile" for nmake on Windows, etc.
  572 
  573 To use the "unified" build system, the target configuration needs to
  574 set the three items 'build_scheme', 'build_file' and 'build_command'.
  575 In the rest of this section, we will assume that 'build_scheme' is set
  576 to "unified" (see the configurations documentation above for the
  577 details).
  578 
  579 For any name given by 'build_file', the "unified" system expects a
  580 template file in Configurations/ named like the build file, with
  581 ".tmpl" appended, or in case of possible ambiguity, a combination of
  582 the second 'build_scheme' list item and the 'build_file' name.  For
  583 example, if 'build_file' is set to "Makefile", the template could be
  584 Configurations/Makefile.tmpl or Configurations/unix-Makefile.tmpl.
  585 In case both Configurations/unix-Makefile.tmpl and
  586 Configurations/Makefile.tmpl are present, the former takes
  587 precedence.
  588 
  589 The build-file template is processed with the perl module
  590 Text::Template, using "{-" and "-}" as delimiters that enclose the
  591 perl code fragments that generate configuration-dependent content.
  592 Those perl fragments have access to all the hash variables from
  593 configdata.pem.
  594 
  595 The build-file template is expected to define at least the following
  596 perl functions in a perl code fragment enclosed with "{-" and "-}".
  597 They are all expected to return a string with the lines they produce.
  598 
  599     generatesrc - function that produces build file lines to generate
  600                   a source file from some input.
  601 
  602                   It's called like this:
  603 
  604                         generatesrc(src => "PATH/TO/tobegenerated",
  605                                     generator => [ "generatingfile", ... ]
  606                                     generator_incs => [ "INCL/PATH", ... ]
  607                                     generator_deps => [ "dep1", ... ]
  608                                     generator => [ "generatingfile", ... ]
  609                                     incs => [ "INCL/PATH", ... ],
  610                                     deps => [ "dep1", ... ],
  611                                     intent => one of "libs", "dso", "bin" );
  612 
  613                   'src' has the name of the file to be generated.
  614                   'generator' is the command or part of command to
  615                   generate the file, of which the first item is
  616                   expected to be the file to generate from.
  617                   generatesrc() is expected to analyse and figure out
  618                   exactly how to apply that file and how to capture
  619                   the result.  'generator_incs' and 'generator_deps'
  620                   are include directories and files that the generator
  621                   file itself depends on.  'incs' and 'deps' are
  622                   include directories and files that are used if $(CC)
  623                   is used as an intermediary step when generating the
  624                   end product (the file indicated by 'src').  'intent'
  625                   indicates what the generated file is going to be
  626                   used for.
  627 
  628     src2obj     - function that produces build file lines to build an
  629                   object file from source files and associated data.
  630 
  631                   It's called like this:
  632 
  633                         src2obj(obj => "PATH/TO/objectfile",
  634                                 srcs => [ "PATH/TO/sourcefile", ... ],
  635                                 deps => [ "dep1", ... ],
  636                                 incs => [ "INCL/PATH", ... ]
  637                                 intent => one of "lib", "dso", "bin" );
  638 
  639                   'obj' has the intended object file *without*
  640                   extension, src2obj() is expected to add that.
  641                   'srcs' has the list of source files to build the
  642                   object file, with the first item being the source
  643                   file that directly corresponds to the object file.
  644                   'deps' is a list of explicit dependencies.  'incs'
  645                   is a list of include file directories.  Finally,
  646                   'intent' indicates what this object file is going
  647                   to be used for.
  648 
  649     obj2lib     - function that produces build file lines to build a
  650                   static library file ("libfoo.a" in Unix terms) from
  651                   object files.
  652 
  653                   called like this:
  654 
  655                         obj2lib(lib => "PATH/TO/libfile",
  656                                 objs => [ "PATH/TO/objectfile", ... ]);
  657 
  658                   'lib' has the intended library file name *without*
  659                   extension, obj2lib is expected to add that.  'objs'
  660                   has the list of object files (also *without*
  661                   extension) to build this library.
  662 
  663     libobj2shlib - function that produces build file lines to build a
  664                   shareable object library file ("libfoo.so" in Unix
  665                   terms) from the corresponding static library file
  666                   or object files.
  667 
  668                   called like this:
  669 
  670                         libobj2shlib(shlib => "PATH/TO/shlibfile",
  671                                      lib => "PATH/TO/libfile",
  672                                      objs => [ "PATH/TO/objectfile", ... ],
  673                                      deps => [ "PATH/TO/otherlibfile", ... ]);
  674 
  675                   'lib' has the intended library file name *without*
  676                   extension, libobj2shlib is expected to add that.
  677                   'shlib' has the corresponding shared library name
  678                   *without* extension.  'deps' has the list of other
  679                   libraries (also *without* extension) this library
  680                   needs to be linked with.  'objs' has the list of
  681                   object files (also *without* extension) to build
  682                   this library.
  683 
  684                   This function has a choice; it can use the
  685                   corresponding static library as input to make the
  686                   shared library, or the list of object files.
  687 
  688     obj2dso     - function that produces build file lines to build a
  689                   dynamic shared object file from object files.
  690 
  691                   called like this:
  692 
  693                         obj2dso(lib => "PATH/TO/libfile",
  694                                 objs => [ "PATH/TO/objectfile", ... ],
  695                                 deps => [ "PATH/TO/otherlibfile",
  696                                 ... ]);
  697 
  698                   This is almost the same as libobj2shlib, but the
  699                   intent is to build a shareable library that can be
  700                   loaded in runtime (a "plugin"...).  The differences
  701                   are subtle, one of the most visible ones is that the
  702                   resulting shareable library is produced from object
  703                   files only.
  704 
  705     obj2bin     - function that produces build file lines to build an
  706                   executable file from object files.
  707 
  708                   called like this:
  709 
  710                         obj2bin(bin => "PATH/TO/binfile",
  711                                 objs => [ "PATH/TO/objectfile", ... ],
  712                                 deps => [ "PATH/TO/libfile", ... ]);
  713 
  714                   'bin' has the intended executable file name
  715                   *without* extension, obj2bin is expected to add
  716                   that.  'objs' has the list of object files (also
  717                   *without* extension) to build this library.  'deps'
  718                   has the list of library files (also *without*
  719                   extension) that the programs needs to be linked
  720                   with.
  721 
  722     in2script   - function that produces build file lines to build a
  723                   script file from some input.
  724 
  725                   called like this:
  726 
  727                         in2script(script => "PATH/TO/scriptfile",
  728                                   sources => [ "PATH/TO/infile", ... ]);
  729 
  730                   'script' has the intended script file name.
  731                   'sources' has the list of source files to build the
  732                   resulting script from.
  733 
  734 In all cases, file file paths are relative to the build tree top, and
  735 the build file actions run with the build tree top as current working
  736 directory.
  737 
  738 Make sure to end the section with these functions with a string that
  739 you thing is appropriate for the resulting build file.  If nothing
  740 else, end it like this:
  741 
  742       "";       # Make sure no lingering values end up in the Makefile
  743     -}
  744 
  745 
  746 Configure helper scripts
  747 ========================
  748 
  749 Configure uses helper scripts in this directory:
  750 
  751 Checker scripts
  752 ---------------
  753 
  754 These scripts are per platform family, to check the integrity of the
  755 tools used for configuration and building.  The checker script used is
  756 either {build_platform}-{build_file}-checker.pm or
  757 {build_platform}-checker.pm, where {build_platform} is the second
  758 'build_scheme' list element from the configuration target data, and
  759 {build_file} is 'build_file' from the same target data.
  760 
  761 If the check succeeds, the script is expected to end with a non-zero
  762 expression.  If the check fails, the script can end with a zero, or
  763 with a `die`.