Configurations/README

   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                            modules, 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         asm_arch        => The architecture to be used for compiling assembly
 169                            source.  This acts as a selector in build.info files.
 170         uplink_arch     => The architecture to be used for compiling uplink
 171                            source.  This acts as a selector in build.info files.
 172                            This is separate from asm_arch because it's compiled
 173                            even when 'no-asm' is given, even though it contains
 174                            assembler source.
 175         perlasm_scheme  => The perlasm method used to create the
 176                            assembler files used when compiling with
 177                            assembler implementations.
 178         shared_target   => The shared library building method used.
 179                            This serves multiple purposes:
 180                            - as index for targets found in shared_info.pl.
 181                            - as linker script generation selector.
 182                            To serve both purposes, the index for shared_info.pl
 183                            should end with '-shared', and this suffix will be
 184                            removed for use as a linker script generation
 185                            selector.  Note that the latter is only used if
 186                            'shared_defflag' is defined.
 187         build_scheme    => The scheme used to build up a Makefile.
 188                            In its simplest form, the value is a string
 189                            with the name of the build scheme.
 190                            The value may also take the form of a list
 191                            of strings, if the build_scheme is to have
 192                            some options.  In this case, the first
 193                            string in the list is the name of the build
 194                            scheme.
 195                            Currently recognised build scheme is "unified".
 196                            For the "unified" build scheme, this item
 197                            *must* be an array with the first being the
 198                            word "unified" and the second being a word
 199                            to identify the platform family.
 200
 201         multilib        => On systems that support having multiple
 202                            implementations of a library (typically a
 203                            32-bit and a 64-bit variant), this is used
 204                            to have the different variants in different
 205                            directories.
 206
 207         bn_ops          => Building options (was just bignum options in
 208                            the earlier history of this option, hence the
 209                            name). This is a string of words that describe
 210                            algorithms' implementation parameters that
 211                            are optimal for the designated target platform,
 212                            such as the type of integers used to build up
 213                            the bignum, different ways to implement certain
 214                            ciphers and so on. To fully comprehend the
 215                            meaning, the best is to read the affected
 216                            source.
 217                            The valid words are:
 218
 219                            THIRTY_TWO_BIT       bignum limbs are 32 bits,
 220                                                 this is default if no
 221                                                 option is specified, it
 222                                                 works on any supported
 223                                                 system [unless "wider"
 224                                                 limb size is implied in
 225                                                 assembly code];
 226                            BN_LLONG             bignum limbs are 32 bits,
 227                                                 but 64-bit 'unsigned long
 228                                                 long' is used internally
 229                                                 in calculations;
 230                            SIXTY_FOUR_BIT_LONG  bignum limbs are 64 bits
 231                                                 and sizeof(long) is 8;
 232                            SIXTY_FOUR_BIT       bignums limbs are 64 bits,
 233                                                 but execution environment
 234                                                 is ILP32;
 235                            RC4_CHAR             RC4 key schedule is made
 236                                                 up of 'unsigned char's;
 237                            RC4_INT              RC4 key schedule is made
 238                                                 up of 'unsigned int's;
 239                            EXPORT_VAR_AS_FN     for shared libraries,
 240                                                 export vars as
 241                                                 accessor functions.
 242
 243         rc4_asm_src     => Assembler implementation of core RC4
 244                            functions.
 245                            Defaults to 'rc4_enc.c rc4_skey.c'
 246         rmd160_asm_src  => Assembler implementation of core RMD160
 247                            functions.
 248         rc5_asm_src     => Assembler implementation of core RC5
 249                            functions.
 250                            Defaults to 'rc5_enc.c'
 251         wp_asm_src      => Assembler implementation of core WHIRLPOOL
 252                            functions.
 253         cmll_asm_src    => Assembler implementation of core CAMELLIA
 254                            functions.
 255                            Defaults to 'camellia.c cmll_misc.c cmll_cbc.c'
 256         modes_asm_src   => Assembler implementation of cipher modes,
 257                            currently the functions gcm_gmult_4bit and
 258                            gcm_ghash_4bit.
 259         padlock_asm_src => Assembler implementation of core parts of
 260                            the padlock engine.  This is mandatory on
 261                            any platform where the padlock engine might
 262                            actually be built.
 263
 264
 265 [1] as part of the target configuration, one can have a key called
 266     'inherit_from' that indicate what other configurations to inherit
 267     data from.  These are resolved recursively.
 268
 269     Inheritance works as a set of default values that can be overridden
 270     by corresponding key values in the inheriting configuration.
 271
 272     Note 1: any configuration table can be used as a template.
 273     Note 2: pure templates have the attribute 'template => 1' and
 274             cannot be used as build targets.
 275
 276     If several configurations are given in the 'inherit_from' array,
 277     the values of same attribute are concatenated with space
 278     separation.  With this, it's possible to have several smaller
 279     templates for different configuration aspects that can be combined
 280     into a complete configuration.
 281
 282     instead of a scalar value or an array, a value can be a code block
 283     of the form 'sub { /* your code here */ }'.  This code block will
 284     be called with the list of inherited values for that key as
 285     arguments.  In fact, the concatenation of strings is really done
 286     by using 'sub { join(" ",@_) }' on the list of inherited values.
 287
 288     An example:
 289
 290         "foo" => {
 291                 template => 1,
 292                 haha => "ha ha",
 293                 hoho => "ho",
 294                 ignored => "This should not appear in the end result",
 295         },
 296         "bar" => {
 297                 template => 1,
 298                 haha => "ah",
 299                 hoho => "haho",
 300                 hehe => "hehe"
 301         },
 302         "laughter" => {
 303                 inherit_from => [ "foo", "bar" ],
 304                 hehe => sub { join(" ",(@_,"!!!")) },
 305                 ignored => "",
 306         }
 307
 308         The entry for "laughter" will become as follows after processing:
 309
 310         "laughter" => {
 311                 haha => "ha ha ah",
 312                 hoho => "ho haho",
 313                 hehe => "hehe !!!",
 314                 ignored => ""
 315         }
 316
 317 [2] OpenSSL is built with threading capabilities unless the user
 318     specifies 'no-threads'.  The value of the key 'thread_scheme' may
 319     be "(unknown)", in which case the user MUST give some compilation
 320     flags to Configure.
 321
 322 [3] OpenSSL has three types of things to link from object files or
 323     static libraries:
 324
 325     - shared libraries; that would be libcrypto and libssl.
 326     - shared objects (sometimes called dynamic libraries);  that would
 327       be the modules.
 328     - applications; those are apps/openssl and all the test apps.
 329
 330     Very roughly speaking, linking is done like this (words in braces
 331     represent the configuration settings documented at the beginning
 332     of this file):
 333
 334     shared libraries:
 335         {ld} $(CFLAGS) {lflags} {shared_ldflag} -o libfoo.so \
 336             foo/something.o foo/somethingelse.o {ex_libs}
 337
 338     shared objects:
 339         {ld} $(CFLAGS) {lflags} {module_ldflags} -o libeng.so \
 340             blah1.o blah2.o -lcrypto {ex_libs}
 341
 342     applications:
 343         {ld} $(CFLAGS) {lflags} -o app \
 344             app1.o utils.o -lssl -lcrypto {ex_libs}
 345
 346 [4] There are variants of these attribute, prefixed with `lib_',
 347     `dso_' or `bin_'.  Those variants replace the unprefixed attribute
 348     when building library, DSO or program modules specifically.
 349
 350 Historically, the target configurations came in form of a string with
 351 values separated by colons.  This use is deprecated.  The string form
 352 looked like this:
 353
 354    "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}"
 355
 356
 357 Build info files
 358 ================
 359
 360 The build.info files that are spread over the source tree contain the
 361 minimum information needed to build and distribute OpenSSL.  It uses a
 362 simple and yet fairly powerful language to determine what needs to be
 363 built, from what sources, and other relationships between files.
 364
 365 For every build.info file, all file references are relative to the
 366 directory of the build.info file for source files, and the
 367 corresponding build directory for built files if the build tree
 368 differs from the source tree.
 369
 370 When processed, every line is processed with the perl module
 371 Text::Template, using the delimiters "{-" and "-}".  The hashes
 372 %config and %target are passed to the perl fragments, along with
 373 $sourcedir and $builddir, which are the locations of the source
 374 directory for the current build.info file and the corresponding build
 375 directory, all relative to the top of the build tree.
 376
 377 'Configure' only knows inherently about the top build.info file.  For
 378 any other directory that has one, further directories to look into
 379 must be indicated like this:
 380
 381     SUBDIRS=something someelse
 382
 383 On to things to be built; they are declared by setting specific
 384 variables:
 385
 386     PROGRAMS=foo bar
 387     LIBS=libsomething
 388     MODULES=libeng
 389     SCRIPTS=myhack
 390
 391 Note that the files mentioned for PROGRAMS, LIBS and MODULES *must* be
 392 without extensions.  The build file templates will figure them out.
 393
 394 For each thing to be built, it is then possible to say what sources
 395 they are built from:
 396
 397     PROGRAMS=foo bar
 398     SOURCE[foo]=foo.c common.c
 399     SOURCE[bar]=bar.c extra.c common.c
 400
 401 It's also possible to tell some other dependencies:
 402
 403     DEPEND[foo]=libsomething
 404     DEPEND[libbar]=libsomethingelse
 405
 406 (it could be argued that 'libsomething' and 'libsomethingelse' are
 407 source as well.  However, the files given through SOURCE are expected
 408 to be located in the source tree while files given through DEPEND are
 409 expected to be located in the build tree)
 410
 411 It's also possible to depend on static libraries explicitly:
 412
 413     DEPEND[foo]=libsomething.a
 414     DEPEND[libbar]=libsomethingelse.a
 415
 416 This should be rarely used, and care should be taken to make sure it's
 417 only used when supported.  For example, native Windows build doesn't
 418 support building static libraries and DLLs at the same time, so using
 419 static libraries on Windows can only be done when configured
 420 'no-shared'.
 421
 422 In some cases, it's desirable to include some source files in the
 423 shared form of a library only:
 424
 425     SHARED_SOURCE[libfoo]=dllmain.c
 426
 427 For any file to be built, it's also possible to tell what extra
 428 include paths the build of their source files should use:
 429
 430     INCLUDE[foo]=include
 431
 432 It's also possible to specify C macros that should be defined:
 433
 434     DEFINE[foo]=FOO BAR=1
 435
 436 In some cases, one might want to generate some source files from
 437 others, that's done as follows:
 438
 439     GENERATE[foo.s]=asm/something.pl $(CFLAGS)
 440     GENERATE[bar.s]=asm/bar.S
 441
 442 The value of each GENERATE line is a command line or part of it.
 443 Configure places no rules on the command line, except that the first
 444 item must be the generator file.  It is, however, entirely up to the
 445 build file template to define exactly how those command lines should
 446 be handled, how the output is captured and so on.
 447
 448 Sometimes, the generator file itself depends on other files, for
 449 example if it is a perl script that depends on other perl modules.
 450 This can be expressed using DEPEND like this:
 451
 452     DEPEND[asm/something.pl]=../perlasm/Foo.pm
 453
 454 There may also be cases where the exact file isn't easily specified,
 455 but an inclusion directory still needs to be specified.  INCLUDE can
 456 be used in that case:
 457
 458     INCLUDE[asm/something.pl]=../perlasm
 459
 460 NOTE: GENERATE lines are limited to one command only per GENERATE.
 461
 462 Finally, you can have some simple conditional use of the build.info
 463 information, looking like this:
 464
 465     IF[1]
 466      something
 467     ELSIF[2]
 468      something other
 469     ELSE
 470      something else
 471     ENDIF
 472
 473 The expression in square brackets is interpreted as a string in perl,
 474 and will be seen as true if perl thinks it is, otherwise false.  For
 475 example, the above would have "something" used, since 1 is true.
 476
 477 Together with the use of Text::Template, this can be used as
 478 conditions based on something in the passed variables, for example:
 479
 480     IF[{- $disabled{shared} -}]
 481       LIBS=libcrypto
 482       SOURCE[libcrypto]=...
 483     ELSE
 484       LIBS=libfoo
 485       SOURCE[libfoo]=...
 486     ENDIF
 487
 488
 489 Build-file programming with the "unified" build system
 490 ======================================================
 491
 492 "Build files" are called "Makefile" on Unix-like operating systems,
 493 "descrip.mms" for MMS on VMS, "makefile" for nmake on Windows, etc.
 494
 495 To use the "unified" build system, the target configuration needs to
 496 set the three items 'build_scheme', 'build_file' and 'build_command'.
 497 In the rest of this section, we will assume that 'build_scheme' is set
 498 to "unified" (see the configurations documentation above for the
 499 details).
 500
 501 For any name given by 'build_file', the "unified" system expects a
 502 template file in Configurations/ named like the build file, with
 503 ".tmpl" appended, or in case of possible ambiguity, a combination of
 504 the second 'build_scheme' list item and the 'build_file' name.  For
 505 example, if 'build_file' is set to "Makefile", the template could be
 506 Configurations/Makefile.tmpl or Configurations/unix-Makefile.tmpl.
 507 In case both Configurations/unix-Makefile.tmpl and
 508 Configurations/Makefile.tmpl are present, the former takes
 509 precedence.
 510
 511 The build-file template is processed with the perl module
 512 Text::Template, using "{-" and "-}" as delimiters that enclose the
 513 perl code fragments that generate configuration-dependent content.
 514 Those perl fragments have access to all the hash variables from
 515 configdata.pem.
 516
 517 The build-file template is expected to define at least the following
 518 perl functions in a perl code fragment enclosed with "{-" and "-}".
 519 They are all expected to return a string with the lines they produce.
 520
 521     generatesrc - function that produces build file lines to generate
 522                   a source file from some input.
 523
 524                   It's called like this:
 525
 526                         generatesrc(src => "PATH/TO/tobegenerated",
 527                                     generator => [ "generatingfile", ... ]
 528                                     generator_incs => [ "INCL/PATH", ... ]
 529                                     generator_deps => [ "dep1", ... ]
 530                                     generator => [ "generatingfile", ... ]
 531                                     incs => [ "INCL/PATH", ... ],
 532                                     deps => [ "dep1", ... ],
 533                                     intent => one of "libs", "dso", "bin" );
 534
 535                   'src' has the name of the file to be generated.
 536                   'generator' is the command or part of command to
 537                   generate the file, of which the first item is
 538                   expected to be the file to generate from.
 539                   generatesrc() is expected to analyse and figure out
 540                   exactly how to apply that file and how to capture
 541                   the result.  'generator_incs' and 'generator_deps'
 542                   are include directories and files that the generator
 543                   file itself depends on.  'incs' and 'deps' are
 544                   include directories and files that are used if $(CC)
 545                   is used as an intermediary step when generating the
 546                   end product (the file indicated by 'src').  'intent'
 547                   indicates what the generated file is going to be
 548                   used for.
 549
 550     src2obj     - function that produces build file lines to build an
 551                   object file from source files and associated data.
 552
 553                   It's called like this:
 554
 555                         src2obj(obj => "PATH/TO/objectfile",
 556                                 srcs => [ "PATH/TO/sourcefile", ... ],
 557                                 deps => [ "dep1", ... ],
 558                                 incs => [ "INCL/PATH", ... ]
 559                                 intent => one of "lib", "dso", "bin" );
 560
 561                   'obj' has the intended object file with '.o'
 562                   extension, src2obj() is expected to change it to
 563                   something more suitable for the platform.
 564                   'srcs' has the list of source files to build the
 565                   object file, with the first item being the source
 566                   file that directly corresponds to the object file.
 567                   'deps' is a list of explicit dependencies.  'incs'
 568                   is a list of include file directories.  Finally,
 569                   'intent' indicates what this object file is going
 570                   to be used for.
 571
 572     obj2lib     - function that produces build file lines to build a
 573                   static library file ("libfoo.a" in Unix terms) from
 574                   object files.
 575
 576                   called like this:
 577
 578                         obj2lib(lib => "PATH/TO/libfile",
 579                                 objs => [ "PATH/TO/objectfile", ... ]);
 580
 581                   'lib' has the intended library file name *without*
 582                   extension, obj2lib is expected to add that.  'objs'
 583                   has the list of object files to build this library.
 584
 585     libobj2shlib - backward compatibility function that's used the
 586                   same way as obj2shlib (described next), and was
 587                   expected to build the shared library from the
 588                   corresponding static library when that was suitable.
 589                   NOTE: building a shared library from a static
 590                   library is now DEPRECATED, as they no longer share
 591                   object files.  Attempting to do this will fail.
 592
 593     obj2shlib   - function that produces build file lines to build a
 594                   shareable object library file ("libfoo.so" in Unix
 595                   terms) from the corresponding object files.
 596
 597                   called like this:
 598
 599                         obj2shlib(shlib => "PATH/TO/shlibfile",
 600                                   lib => "PATH/TO/libfile",
 601                                   objs => [ "PATH/TO/objectfile", ... ],
 602                                   deps => [ "PATH/TO/otherlibfile", ... ]);
 603
 604                   'lib' has the base (static) library ffile name
 605                   *without* extension.  This is useful in case
 606                   supporting files are needed (such as import
 607                   libraries on Windows).
 608                   'shlib' has the corresponding shared library name
 609                   *without* extension.  'deps' has the list of other
 610                   libraries (also *without* extension) this library
 611                   needs to be linked with.  'objs' has the list of
 612                   object files to build this library.
 613
 614     obj2dso     - function that produces build file lines to build a
 615                   dynamic shared object file from object files.
 616
 617                   called like this:
 618
 619                         obj2dso(lib => "PATH/TO/libfile",
 620                                 objs => [ "PATH/TO/objectfile", ... ],
 621                                 deps => [ "PATH/TO/otherlibfile",
 622                                 ... ]);
 623
 624                   This is almost the same as obj2shlib, but the
 625                   intent is to build a shareable library that can be
 626                   loaded in runtime (a "plugin"...).
 627
 628     obj2bin     - function that produces build file lines to build an
 629                   executable file from object files.
 630
 631                   called like this:
 632
 633                         obj2bin(bin => "PATH/TO/binfile",
 634                                 objs => [ "PATH/TO/objectfile", ... ],
 635                                 deps => [ "PATH/TO/libfile", ... ]);
 636
 637                   'bin' has the intended executable file name
 638                   *without* extension, obj2bin is expected to add
 639                   that.  'objs' has the list of object files to build
 640                   this library.  'deps' has the list of library files
 641                   (also *without* extension) that the programs needs
 642                   to be linked with.
 643
 644     in2script   - function that produces build file lines to build a
 645                   script file from some input.
 646
 647                   called like this:
 648
 649                         in2script(script => "PATH/TO/scriptfile",
 650                                   sources => [ "PATH/TO/infile", ... ]);
 651
 652                   'script' has the intended script file name.
 653                   'sources' has the list of source files to build the
 654                   resulting script from.
 655
 656 In all cases, file file paths are relative to the build tree top, and
 657 the build file actions run with the build tree top as current working
 658 directory.
 659
 660 Make sure to end the section with these functions with a string that
 661 you thing is appropriate for the resulting build file.  If nothing
 662 else, end it like this:
 663
 664       "";       # Make sure no lingering values end up in the Makefile
 665     -}
 666
 667
 668 Configure helper scripts
 669 ========================
 670
 671 Configure uses helper scripts in this directory:
 672
 673 Checker scripts
 674 ---------------
 675
 676 These scripts are per platform family, to check the integrity of the
 677 tools used for configuration and building.  The checker script used is
 678 either {build_platform}-{build_file}-checker.pm or
 679 {build_platform}-checker.pm, where {build_platform} is the second
 680 'build_scheme' list element from the configuration target data, and
 681 {build_file} is 'build_file' from the same target data.
 682
 683 If the check succeeds, the script is expected to end with a non-zero
 684 expression.  If the check fails, the script can end with a zero, or
 685 with a `die`.