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         sha1_asm_src    => Assembler implementation of core SHA1,
 244                            functions, and also possibly SHA256 and
 245                            SHA512 ones.
 246         cast_asm_src    => Assembler implementation of core CAST
 247                            functions.
 248                            Defaults to 'c_enc.c'
 249         rc4_asm_src     => Assembler implementation of core RC4
 250                            functions.
 251                            Defaults to 'rc4_enc.c rc4_skey.c'
 252         rmd160_asm_src  => Assembler implementation of core RMD160
 253                            functions.
 254         rc5_asm_src     => Assembler implementation of core RC5
 255                            functions.
 256                            Defaults to 'rc5_enc.c'
 257         wp_asm_src      => Assembler implementation of core WHIRLPOOL
 258                            functions.
 259         cmll_asm_src    => Assembler implementation of core CAMELLIA
 260                            functions.
 261                            Defaults to 'camellia.c cmll_misc.c cmll_cbc.c'
 262         modes_asm_src   => Assembler implementation of cipher modes,
 263                            currently the functions gcm_gmult_4bit and
 264                            gcm_ghash_4bit.
 265         padlock_asm_src => Assembler implementation of core parts of
 266                            the padlock engine.  This is mandatory on
 267                            any platform where the padlock engine might
 268                            actually be built.
 269
 270
 271 [1] as part of the target configuration, one can have a key called
 272     'inherit_from' that indicate what other configurations to inherit
 273     data from.  These are resolved recursively.
 274
 275     Inheritance works as a set of default values that can be overridden
 276     by corresponding key values in the inheriting configuration.
 277
 278     Note 1: any configuration table can be used as a template.
 279     Note 2: pure templates have the attribute 'template => 1' and
 280             cannot be used as build targets.
 281
 282     If several configurations are given in the 'inherit_from' array,
 283     the values of same attribute are concatenated with space
 284     separation.  With this, it's possible to have several smaller
 285     templates for different configuration aspects that can be combined
 286     into a complete configuration.
 287
 288     instead of a scalar value or an array, a value can be a code block
 289     of the form 'sub { /* your code here */ }'.  This code block will
 290     be called with the list of inherited values for that key as
 291     arguments.  In fact, the concatenation of strings is really done
 292     by using 'sub { join(" ",@_) }' on the list of inherited values.
 293
 294     An example:
 295
 296         "foo" => {
 297                 template => 1,
 298                 haha => "ha ha",
 299                 hoho => "ho",
 300                 ignored => "This should not appear in the end result",
 301         },
 302         "bar" => {
 303                 template => 1,
 304                 haha => "ah",
 305                 hoho => "haho",
 306                 hehe => "hehe"
 307         },
 308         "laughter" => {
 309                 inherit_from => [ "foo", "bar" ],
 310                 hehe => sub { join(" ",(@_,"!!!")) },
 311                 ignored => "",
 312         }
 313
 314         The entry for "laughter" will become as follows after processing:
 315
 316         "laughter" => {
 317                 haha => "ha ha ah",
 318                 hoho => "ho haho",
 319                 hehe => "hehe !!!",
 320                 ignored => ""
 321         }
 322
 323 [2] OpenSSL is built with threading capabilities unless the user
 324     specifies 'no-threads'.  The value of the key 'thread_scheme' may
 325     be "(unknown)", in which case the user MUST give some compilation
 326     flags to Configure.
 327
 328 [3] OpenSSL has three types of things to link from object files or
 329     static libraries:
 330
 331     - shared libraries; that would be libcrypto and libssl.
 332     - shared objects (sometimes called dynamic libraries);  that would
 333       be the modules.
 334     - applications; those are apps/openssl and all the test apps.
 335
 336     Very roughly speaking, linking is done like this (words in braces
 337     represent the configuration settings documented at the beginning
 338     of this file):
 339
 340     shared libraries:
 341         {ld} $(CFLAGS) {lflags} {shared_ldflag} -o libfoo.so \
 342             foo/something.o foo/somethingelse.o {ex_libs}
 343
 344     shared objects:
 345         {ld} $(CFLAGS) {lflags} {module_ldflags} -o libeng.so \
 346             blah1.o blah2.o -lcrypto {ex_libs}
 347
 348     applications:
 349         {ld} $(CFLAGS) {lflags} -o app \
 350             app1.o utils.o -lssl -lcrypto {ex_libs}
 351
 352 [4] There are variants of these attribute, prefixed with `lib_',
 353     `dso_' or `bin_'.  Those variants replace the unprefixed attribute
 354     when building library, DSO or program modules specifically.
 355
 356 Historically, the target configurations came in form of a string with
 357 values separated by colons.  This use is deprecated.  The string form
 358 looked like this:
 359
 360    "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}"
 361
 362
 363 Build info files
 364 ================
 365
 366 The build.info files that are spread over the source tree contain the
 367 minimum information needed to build and distribute OpenSSL.  It uses a
 368 simple and yet fairly powerful language to determine what needs to be
 369 built, from what sources, and other relationships between files.
 370
 371 For every build.info file, all file references are relative to the
 372 directory of the build.info file for source files, and the
 373 corresponding build directory for built files if the build tree
 374 differs from the source tree.
 375
 376 When processed, every line is processed with the perl module
 377 Text::Template, using the delimiters "{-" and "-}".  The hashes
 378 %config and %target are passed to the perl fragments, along with
 379 $sourcedir and $builddir, which are the locations of the source
 380 directory for the current build.info file and the corresponding build
 381 directory, all relative to the top of the build tree.
 382
 383 'Configure' only knows inherently about the top build.info file.  For
 384 any other directory that has one, further directories to look into
 385 must be indicated like this:
 386
 387     SUBDIRS=something someelse
 388
 389 On to things to be built; they are declared by setting specific
 390 variables:
 391
 392     PROGRAMS=foo bar
 393     LIBS=libsomething
 394     MODULES=libeng
 395     SCRIPTS=myhack
 396
 397 Note that the files mentioned for PROGRAMS, LIBS and MODULES *must* be
 398 without extensions.  The build file templates will figure them out.
 399
 400 For each thing to be built, it is then possible to say what sources
 401 they are built from:
 402
 403     PROGRAMS=foo bar
 404     SOURCE[foo]=foo.c common.c
 405     SOURCE[bar]=bar.c extra.c common.c
 406
 407 It's also possible to tell some other dependencies:
 408
 409     DEPEND[foo]=libsomething
 410     DEPEND[libbar]=libsomethingelse
 411
 412 (it could be argued that 'libsomething' and 'libsomethingelse' are
 413 source as well.  However, the files given through SOURCE are expected
 414 to be located in the source tree while files given through DEPEND are
 415 expected to be located in the build tree)
 416
 417 It's also possible to depend on static libraries explicitly:
 418
 419     DEPEND[foo]=libsomething.a
 420     DEPEND[libbar]=libsomethingelse.a
 421
 422 This should be rarely used, and care should be taken to make sure it's
 423 only used when supported.  For example, native Windows build doesn't
 424 support building static libraries and DLLs at the same time, so using
 425 static libraries on Windows can only be done when configured
 426 'no-shared'.
 427
 428 In some cases, it's desirable to include some source files in the
 429 shared form of a library only:
 430
 431     SHARED_SOURCE[libfoo]=dllmain.c
 432
 433 For any file to be built, it's also possible to tell what extra
 434 include paths the build of their source files should use:
 435
 436     INCLUDE[foo]=include
 437
 438 It's also possible to specify C macros that should be defined:
 439
 440     DEFINE[foo]=FOO BAR=1
 441
 442 In some cases, one might want to generate some source files from
 443 others, that's done as follows:
 444
 445     GENERATE[foo.s]=asm/something.pl $(CFLAGS)
 446     GENERATE[bar.s]=asm/bar.S
 447
 448 The value of each GENERATE line is a command line or part of it.
 449 Configure places no rules on the command line, except that the first
 450 item must be the generator file.  It is, however, entirely up to the
 451 build file template to define exactly how those command lines should
 452 be handled, how the output is captured and so on.
 453
 454 Sometimes, the generator file itself depends on other files, for
 455 example if it is a perl script that depends on other perl modules.
 456 This can be expressed using DEPEND like this:
 457
 458     DEPEND[asm/something.pl]=../perlasm/Foo.pm
 459
 460 There may also be cases where the exact file isn't easily specified,
 461 but an inclusion directory still needs to be specified.  INCLUDE can
 462 be used in that case:
 463
 464     INCLUDE[asm/something.pl]=../perlasm
 465
 466 NOTE: GENERATE lines are limited to one command only per GENERATE.
 467
 468 Finally, you can have some simple conditional use of the build.info
 469 information, looking like this:
 470
 471     IF[1]
 472      something
 473     ELSIF[2]
 474      something other
 475     ELSE
 476      something else
 477     ENDIF
 478
 479 The expression in square brackets is interpreted as a string in perl,
 480 and will be seen as true if perl thinks it is, otherwise false.  For
 481 example, the above would have "something" used, since 1 is true.
 482
 483 Together with the use of Text::Template, this can be used as
 484 conditions based on something in the passed variables, for example:
 485
 486     IF[{- $disabled{shared} -}]
 487       LIBS=libcrypto
 488       SOURCE[libcrypto]=...
 489     ELSE
 490       LIBS=libfoo
 491       SOURCE[libfoo]=...
 492     ENDIF
 493
 494
 495 Build-file programming with the "unified" build system
 496 ======================================================
 497
 498 "Build files" are called "Makefile" on Unix-like operating systems,
 499 "descrip.mms" for MMS on VMS, "makefile" for nmake on Windows, etc.
 500
 501 To use the "unified" build system, the target configuration needs to
 502 set the three items 'build_scheme', 'build_file' and 'build_command'.
 503 In the rest of this section, we will assume that 'build_scheme' is set
 504 to "unified" (see the configurations documentation above for the
 505 details).
 506
 507 For any name given by 'build_file', the "unified" system expects a
 508 template file in Configurations/ named like the build file, with
 509 ".tmpl" appended, or in case of possible ambiguity, a combination of
 510 the second 'build_scheme' list item and the 'build_file' name.  For
 511 example, if 'build_file' is set to "Makefile", the template could be
 512 Configurations/Makefile.tmpl or Configurations/unix-Makefile.tmpl.
 513 In case both Configurations/unix-Makefile.tmpl and
 514 Configurations/Makefile.tmpl are present, the former takes
 515 precedence.
 516
 517 The build-file template is processed with the perl module
 518 Text::Template, using "{-" and "-}" as delimiters that enclose the
 519 perl code fragments that generate configuration-dependent content.
 520 Those perl fragments have access to all the hash variables from
 521 configdata.pem.
 522
 523 The build-file template is expected to define at least the following
 524 perl functions in a perl code fragment enclosed with "{-" and "-}".
 525 They are all expected to return a string with the lines they produce.
 526
 527     generatesrc - function that produces build file lines to generate
 528                   a source file from some input.
 529
 530                   It's called like this:
 531
 532                         generatesrc(src => "PATH/TO/tobegenerated",
 533                                     generator => [ "generatingfile", ... ]
 534                                     generator_incs => [ "INCL/PATH", ... ]
 535                                     generator_deps => [ "dep1", ... ]
 536                                     generator => [ "generatingfile", ... ]
 537                                     incs => [ "INCL/PATH", ... ],
 538                                     deps => [ "dep1", ... ],
 539                                     intent => one of "libs", "dso", "bin" );
 540
 541                   'src' has the name of the file to be generated.
 542                   'generator' is the command or part of command to
 543                   generate the file, of which the first item is
 544                   expected to be the file to generate from.
 545                   generatesrc() is expected to analyse and figure out
 546                   exactly how to apply that file and how to capture
 547                   the result.  'generator_incs' and 'generator_deps'
 548                   are include directories and files that the generator
 549                   file itself depends on.  'incs' and 'deps' are
 550                   include directories and files that are used if $(CC)
 551                   is used as an intermediary step when generating the
 552                   end product (the file indicated by 'src').  'intent'
 553                   indicates what the generated file is going to be
 554                   used for.
 555
 556     src2obj     - function that produces build file lines to build an
 557                   object file from source files and associated data.
 558
 559                   It's called like this:
 560
 561                         src2obj(obj => "PATH/TO/objectfile",
 562                                 srcs => [ "PATH/TO/sourcefile", ... ],
 563                                 deps => [ "dep1", ... ],
 564                                 incs => [ "INCL/PATH", ... ]
 565                                 intent => one of "lib", "dso", "bin" );
 566
 567                   'obj' has the intended object file with '.o'
 568                   extension, src2obj() is expected to change it to
 569                   something more suitable for the platform.
 570                   'srcs' has the list of source files to build the
 571                   object file, with the first item being the source
 572                   file that directly corresponds to the object file.
 573                   'deps' is a list of explicit dependencies.  'incs'
 574                   is a list of include file directories.  Finally,
 575                   'intent' indicates what this object file is going
 576                   to be used for.
 577
 578     obj2lib     - function that produces build file lines to build a
 579                   static library file ("libfoo.a" in Unix terms) from
 580                   object files.
 581
 582                   called like this:
 583
 584                         obj2lib(lib => "PATH/TO/libfile",
 585                                 objs => [ "PATH/TO/objectfile", ... ]);
 586
 587                   'lib' has the intended library file name *without*
 588                   extension, obj2lib is expected to add that.  'objs'
 589                   has the list of object files to build this library.
 590
 591     libobj2shlib - backward compatibility function that's used the
 592                   same way as obj2shlib (described next), and was
 593                   expected to build the shared library from the
 594                   corresponding static library when that was suitable.
 595                   NOTE: building a shared library from a static
 596                   library is now DEPRECATED, as they no longer share
 597                   object files.  Attempting to do this will fail.
 598
 599     obj2shlib   - function that produces build file lines to build a
 600                   shareable object library file ("libfoo.so" in Unix
 601                   terms) from the corresponding object files.
 602
 603                   called like this:
 604
 605                         obj2shlib(shlib => "PATH/TO/shlibfile",
 606                                   lib => "PATH/TO/libfile",
 607                                   objs => [ "PATH/TO/objectfile", ... ],
 608                                   deps => [ "PATH/TO/otherlibfile", ... ]);
 609
 610                   'lib' has the base (static) library ffile name
 611                   *without* extension.  This is useful in case
 612                   supporting files are needed (such as import
 613                   libraries on Windows).
 614                   'shlib' has the corresponding shared library name
 615                   *without* extension.  'deps' has the list of other
 616                   libraries (also *without* extension) this library
 617                   needs to be linked with.  'objs' has the list of
 618                   object files to build this library.
 619
 620     obj2dso     - function that produces build file lines to build a
 621                   dynamic shared object file from object files.
 622
 623                   called like this:
 624
 625                         obj2dso(lib => "PATH/TO/libfile",
 626                                 objs => [ "PATH/TO/objectfile", ... ],
 627                                 deps => [ "PATH/TO/otherlibfile",
 628                                 ... ]);
 629
 630                   This is almost the same as obj2shlib, but the
 631                   intent is to build a shareable library that can be
 632                   loaded in runtime (a "plugin"...).
 633
 634     obj2bin     - function that produces build file lines to build an
 635                   executable file from object files.
 636
 637                   called like this:
 638
 639                         obj2bin(bin => "PATH/TO/binfile",
 640                                 objs => [ "PATH/TO/objectfile", ... ],
 641                                 deps => [ "PATH/TO/libfile", ... ]);
 642
 643                   'bin' has the intended executable file name
 644                   *without* extension, obj2bin is expected to add
 645                   that.  'objs' has the list of object files to build
 646                   this library.  'deps' has the list of library files
 647                   (also *without* extension) that the programs needs
 648                   to be linked with.
 649
 650     in2script   - function that produces build file lines to build a
 651                   script file from some input.
 652
 653                   called like this:
 654
 655                         in2script(script => "PATH/TO/scriptfile",
 656                                   sources => [ "PATH/TO/infile", ... ]);
 657
 658                   'script' has the intended script file name.
 659                   'sources' has the list of source files to build the
 660                   resulting script from.
 661
 662 In all cases, file file paths are relative to the build tree top, and
 663 the build file actions run with the build tree top as current working
 664 directory.
 665
 666 Make sure to end the section with these functions with a string that
 667 you thing is appropriate for the resulting build file.  If nothing
 668 else, end it like this:
 669
 670       "";       # Make sure no lingering values end up in the Makefile
 671     -}
 672
 673
 674 Configure helper scripts
 675 ========================
 676
 677 Configure uses helper scripts in this directory:
 678
 679 Checker scripts
 680 ---------------
 681
 682 These scripts are per platform family, to check the integrity of the
 683 tools used for configuration and building.  The checker script used is
 684 either {build_platform}-{build_file}-checker.pm or
 685 {build_platform}-checker.pm, where {build_platform} is the second
 686 'build_scheme' list element from the configuration target data, and
 687 {build_file} is 'build_file' from the same target data.
 688
 689 If the check succeeds, the script is expected to end with a non-zero
 690 expression.  If the check fails, the script can end with a zero, or
 691 with a `die`.