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         des_asm_src     => Assembler implementation of core DES
 244                            encryption functions.
 245                            Defaults to 'des_enc.c fcrypt_b.c'
 246         aes_asm_src     => Assembler implementation of core AES
 247                            functions.
 248                            Defaults to 'aes_core.c aes_cbc.c'
 249         bf_asm_src      => Assembler implementation of core BlowFish
 250                            functions.
 251                            Defaults to 'bf_enc.c'
 252         md5_asm_src     => Assembler implementation of core MD5
 253                            functions.
 254         sha1_asm_src    => Assembler implementation of core SHA1,
 255                            functions, and also possibly SHA256 and
 256                            SHA512 ones.
 257         cast_asm_src    => Assembler implementation of core CAST
 258                            functions.
 259                            Defaults to 'c_enc.c'
 260         rc4_asm_src     => Assembler implementation of core RC4
 261                            functions.
 262                            Defaults to 'rc4_enc.c rc4_skey.c'
 263         rmd160_asm_src  => Assembler implementation of core RMD160
 264                            functions.
 265         rc5_asm_src     => Assembler implementation of core RC5
 266                            functions.
 267                            Defaults to 'rc5_enc.c'
 268         wp_asm_src      => Assembler implementation of core WHIRLPOOL
 269                            functions.
 270         cmll_asm_src    => Assembler implementation of core CAMELLIA
 271                            functions.
 272                            Defaults to 'camellia.c cmll_misc.c cmll_cbc.c'
 273         modes_asm_src   => Assembler implementation of cipher modes,
 274                            currently the functions gcm_gmult_4bit and
 275                            gcm_ghash_4bit.
 276         padlock_asm_src => Assembler implementation of core parts of
 277                            the padlock engine.  This is mandatory on
 278                            any platform where the padlock engine might
 279                            actually be built.
 280
 281
 282 [1] as part of the target configuration, one can have a key called
 283     'inherit_from' that indicate what other configurations to inherit
 284     data from.  These are resolved recursively.
 285
 286     Inheritance works as a set of default values that can be overridden
 287     by corresponding key values in the inheriting configuration.
 288
 289     Note 1: any configuration table can be used as a template.
 290     Note 2: pure templates have the attribute 'template => 1' and
 291             cannot be used as build targets.
 292
 293     If several configurations are given in the 'inherit_from' array,
 294     the values of same attribute are concatenated with space
 295     separation.  With this, it's possible to have several smaller
 296     templates for different configuration aspects that can be combined
 297     into a complete configuration.
 298
 299     instead of a scalar value or an array, a value can be a code block
 300     of the form 'sub { /* your code here */ }'.  This code block will
 301     be called with the list of inherited values for that key as
 302     arguments.  In fact, the concatenation of strings is really done
 303     by using 'sub { join(" ",@_) }' on the list of inherited values.
 304
 305     An example:
 306
 307         "foo" => {
 308                 template => 1,
 309                 haha => "ha ha",
 310                 hoho => "ho",
 311                 ignored => "This should not appear in the end result",
 312         },
 313         "bar" => {
 314                 template => 1,
 315                 haha => "ah",
 316                 hoho => "haho",
 317                 hehe => "hehe"
 318         },
 319         "laughter" => {
 320                 inherit_from => [ "foo", "bar" ],
 321                 hehe => sub { join(" ",(@_,"!!!")) },
 322                 ignored => "",
 323         }
 324
 325         The entry for "laughter" will become as follows after processing:
 326
 327         "laughter" => {
 328                 haha => "ha ha ah",
 329                 hoho => "ho haho",
 330                 hehe => "hehe !!!",
 331                 ignored => ""
 332         }
 333
 334 [2] OpenSSL is built with threading capabilities unless the user
 335     specifies 'no-threads'.  The value of the key 'thread_scheme' may
 336     be "(unknown)", in which case the user MUST give some compilation
 337     flags to Configure.
 338
 339 [3] OpenSSL has three types of things to link from object files or
 340     static libraries:
 341
 342     - shared libraries; that would be libcrypto and libssl.
 343     - shared objects (sometimes called dynamic libraries);  that would
 344       be the modules.
 345     - applications; those are apps/openssl and all the test apps.
 346
 347     Very roughly speaking, linking is done like this (words in braces
 348     represent the configuration settings documented at the beginning
 349     of this file):
 350
 351     shared libraries:
 352         {ld} $(CFLAGS) {lflags} {shared_ldflag} -o libfoo.so \
 353             foo/something.o foo/somethingelse.o {ex_libs}
 354
 355     shared objects:
 356         {ld} $(CFLAGS) {lflags} {module_ldflags} -o libeng.so \
 357             blah1.o blah2.o -lcrypto {ex_libs}
 358
 359     applications:
 360         {ld} $(CFLAGS) {lflags} -o app \
 361             app1.o utils.o -lssl -lcrypto {ex_libs}
 362
 363 [4] There are variants of these attribute, prefixed with `lib_',
 364     `dso_' or `bin_'.  Those variants replace the unprefixed attribute
 365     when building library, DSO or program modules specifically.
 366
 367 Historically, the target configurations came in form of a string with
 368 values separated by colons.  This use is deprecated.  The string form
 369 looked like this:
 370
 371    "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}"
 372
 373
 374 Build info files
 375 ================
 376
 377 The build.info files that are spread over the source tree contain the
 378 minimum information needed to build and distribute OpenSSL.  It uses a
 379 simple and yet fairly powerful language to determine what needs to be
 380 built, from what sources, and other relationships between files.
 381
 382 For every build.info file, all file references are relative to the
 383 directory of the build.info file for source files, and the
 384 corresponding build directory for built files if the build tree
 385 differs from the source tree.
 386
 387 When processed, every line is processed with the perl module
 388 Text::Template, using the delimiters "{-" and "-}".  The hashes
 389 %config and %target are passed to the perl fragments, along with
 390 $sourcedir and $builddir, which are the locations of the source
 391 directory for the current build.info file and the corresponding build
 392 directory, all relative to the top of the build tree.
 393
 394 'Configure' only knows inherently about the top build.info file.  For
 395 any other directory that has one, further directories to look into
 396 must be indicated like this:
 397
 398     SUBDIRS=something someelse
 399
 400 On to things to be built; they are declared by setting specific
 401 variables:
 402
 403     PROGRAMS=foo bar
 404     LIBS=libsomething
 405     MODULES=libeng
 406     SCRIPTS=myhack
 407
 408 Note that the files mentioned for PROGRAMS, LIBS and MODULES *must* be
 409 without extensions.  The build file templates will figure them out.
 410
 411 For each thing to be built, it is then possible to say what sources
 412 they are built from:
 413
 414     PROGRAMS=foo bar
 415     SOURCE[foo]=foo.c common.c
 416     SOURCE[bar]=bar.c extra.c common.c
 417
 418 It's also possible to tell some other dependencies:
 419
 420     DEPEND[foo]=libsomething
 421     DEPEND[libbar]=libsomethingelse
 422
 423 (it could be argued that 'libsomething' and 'libsomethingelse' are
 424 source as well.  However, the files given through SOURCE are expected
 425 to be located in the source tree while files given through DEPEND are
 426 expected to be located in the build tree)
 427
 428 It's also possible to depend on static libraries explicitly:
 429
 430     DEPEND[foo]=libsomething.a
 431     DEPEND[libbar]=libsomethingelse.a
 432
 433 This should be rarely used, and care should be taken to make sure it's
 434 only used when supported.  For example, native Windows build doesn't
 435 support building static libraries and DLLs at the same time, so using
 436 static libraries on Windows can only be done when configured
 437 'no-shared'.
 438
 439 In some cases, it's desirable to include some source files in the
 440 shared form of a library only:
 441
 442     SHARED_SOURCE[libfoo]=dllmain.c
 443
 444 For any file to be built, it's also possible to tell what extra
 445 include paths the build of their source files should use:
 446
 447     INCLUDE[foo]=include
 448
 449 It's also possible to specify C macros that should be defined:
 450
 451     DEFINE[foo]=FOO BAR=1
 452
 453 In some cases, one might want to generate some source files from
 454 others, that's done as follows:
 455
 456     GENERATE[foo.s]=asm/something.pl $(CFLAGS)
 457     GENERATE[bar.s]=asm/bar.S
 458
 459 The value of each GENERATE line is a command line or part of it.
 460 Configure places no rules on the command line, except that the first
 461 item must be the generator file.  It is, however, entirely up to the
 462 build file template to define exactly how those command lines should
 463 be handled, how the output is captured and so on.
 464
 465 Sometimes, the generator file itself depends on other files, for
 466 example if it is a perl script that depends on other perl modules.
 467 This can be expressed using DEPEND like this:
 468
 469     DEPEND[asm/something.pl]=../perlasm/Foo.pm
 470
 471 There may also be cases where the exact file isn't easily specified,
 472 but an inclusion directory still needs to be specified.  INCLUDE can
 473 be used in that case:
 474
 475     INCLUDE[asm/something.pl]=../perlasm
 476
 477 NOTE: GENERATE lines are limited to one command only per GENERATE.
 478
 479 Finally, you can have some simple conditional use of the build.info
 480 information, looking like this:
 481
 482     IF[1]
 483      something
 484     ELSIF[2]
 485      something other
 486     ELSE
 487      something else
 488     ENDIF
 489
 490 The expression in square brackets is interpreted as a string in perl,
 491 and will be seen as true if perl thinks it is, otherwise false.  For
 492 example, the above would have "something" used, since 1 is true.
 493
 494 Together with the use of Text::Template, this can be used as
 495 conditions based on something in the passed variables, for example:
 496
 497     IF[{- $disabled{shared} -}]
 498       LIBS=libcrypto
 499       SOURCE[libcrypto]=...
 500     ELSE
 501       LIBS=libfoo
 502       SOURCE[libfoo]=...
 503     ENDIF
 504
 505
 506 Build-file programming with the "unified" build system
 507 ======================================================
 508
 509 "Build files" are called "Makefile" on Unix-like operating systems,
 510 "descrip.mms" for MMS on VMS, "makefile" for nmake on Windows, etc.
 511
 512 To use the "unified" build system, the target configuration needs to
 513 set the three items 'build_scheme', 'build_file' and 'build_command'.
 514 In the rest of this section, we will assume that 'build_scheme' is set
 515 to "unified" (see the configurations documentation above for the
 516 details).
 517
 518 For any name given by 'build_file', the "unified" system expects a
 519 template file in Configurations/ named like the build file, with
 520 ".tmpl" appended, or in case of possible ambiguity, a combination of
 521 the second 'build_scheme' list item and the 'build_file' name.  For
 522 example, if 'build_file' is set to "Makefile", the template could be
 523 Configurations/Makefile.tmpl or Configurations/unix-Makefile.tmpl.
 524 In case both Configurations/unix-Makefile.tmpl and
 525 Configurations/Makefile.tmpl are present, the former takes
 526 precedence.
 527
 528 The build-file template is processed with the perl module
 529 Text::Template, using "{-" and "-}" as delimiters that enclose the
 530 perl code fragments that generate configuration-dependent content.
 531 Those perl fragments have access to all the hash variables from
 532 configdata.pem.
 533
 534 The build-file template is expected to define at least the following
 535 perl functions in a perl code fragment enclosed with "{-" and "-}".
 536 They are all expected to return a string with the lines they produce.
 537
 538     generatesrc - function that produces build file lines to generate
 539                   a source file from some input.
 540
 541                   It's called like this:
 542
 543                         generatesrc(src => "PATH/TO/tobegenerated",
 544                                     generator => [ "generatingfile", ... ]
 545                                     generator_incs => [ "INCL/PATH", ... ]
 546                                     generator_deps => [ "dep1", ... ]
 547                                     generator => [ "generatingfile", ... ]
 548                                     incs => [ "INCL/PATH", ... ],
 549                                     deps => [ "dep1", ... ],
 550                                     intent => one of "libs", "dso", "bin" );
 551
 552                   'src' has the name of the file to be generated.
 553                   'generator' is the command or part of command to
 554                   generate the file, of which the first item is
 555                   expected to be the file to generate from.
 556                   generatesrc() is expected to analyse and figure out
 557                   exactly how to apply that file and how to capture
 558                   the result.  'generator_incs' and 'generator_deps'
 559                   are include directories and files that the generator
 560                   file itself depends on.  'incs' and 'deps' are
 561                   include directories and files that are used if $(CC)
 562                   is used as an intermediary step when generating the
 563                   end product (the file indicated by 'src').  'intent'
 564                   indicates what the generated file is going to be
 565                   used for.
 566
 567     src2obj     - function that produces build file lines to build an
 568                   object file from source files and associated data.
 569
 570                   It's called like this:
 571
 572                         src2obj(obj => "PATH/TO/objectfile",
 573                                 srcs => [ "PATH/TO/sourcefile", ... ],
 574                                 deps => [ "dep1", ... ],
 575                                 incs => [ "INCL/PATH", ... ]
 576                                 intent => one of "lib", "dso", "bin" );
 577
 578                   'obj' has the intended object file with '.o'
 579                   extension, src2obj() is expected to change it to
 580                   something more suitable for the platform.
 581                   'srcs' has the list of source files to build the
 582                   object file, with the first item being the source
 583                   file that directly corresponds to the object file.
 584                   'deps' is a list of explicit dependencies.  'incs'
 585                   is a list of include file directories.  Finally,
 586                   'intent' indicates what this object file is going
 587                   to be used for.
 588
 589     obj2lib     - function that produces build file lines to build a
 590                   static library file ("libfoo.a" in Unix terms) from
 591                   object files.
 592
 593                   called like this:
 594
 595                         obj2lib(lib => "PATH/TO/libfile",
 596                                 objs => [ "PATH/TO/objectfile", ... ]);
 597
 598                   'lib' has the intended library file name *without*
 599                   extension, obj2lib is expected to add that.  'objs'
 600                   has the list of object files to build this library.
 601
 602     libobj2shlib - backward compatibility function that's used the
 603                   same way as obj2shlib (described next), and was
 604                   expected to build the shared library from the
 605                   corresponding static library when that was suitable.
 606                   NOTE: building a shared library from a static
 607                   library is now DEPRECATED, as they no longer share
 608                   object files.  Attempting to do this will fail.
 609
 610     obj2shlib   - function that produces build file lines to build a
 611                   shareable object library file ("libfoo.so" in Unix
 612                   terms) from the corresponding object files.
 613
 614                   called like this:
 615
 616                         obj2shlib(shlib => "PATH/TO/shlibfile",
 617                                   lib => "PATH/TO/libfile",
 618                                   objs => [ "PATH/TO/objectfile", ... ],
 619                                   deps => [ "PATH/TO/otherlibfile", ... ]);
 620
 621                   'lib' has the base (static) library ffile name
 622                   *without* extension.  This is useful in case
 623                   supporting files are needed (such as import
 624                   libraries on Windows).
 625                   'shlib' has the corresponding shared library name
 626                   *without* extension.  'deps' has the list of other
 627                   libraries (also *without* extension) this library
 628                   needs to be linked with.  'objs' has the list of
 629                   object files to build this library.
 630
 631     obj2dso     - function that produces build file lines to build a
 632                   dynamic shared object file from object files.
 633
 634                   called like this:
 635
 636                         obj2dso(lib => "PATH/TO/libfile",
 637                                 objs => [ "PATH/TO/objectfile", ... ],
 638                                 deps => [ "PATH/TO/otherlibfile",
 639                                 ... ]);
 640
 641                   This is almost the same as obj2shlib, but the
 642                   intent is to build a shareable library that can be
 643                   loaded in runtime (a "plugin"...).
 644
 645     obj2bin     - function that produces build file lines to build an
 646                   executable file from object files.
 647
 648                   called like this:
 649
 650                         obj2bin(bin => "PATH/TO/binfile",
 651                                 objs => [ "PATH/TO/objectfile", ... ],
 652                                 deps => [ "PATH/TO/libfile", ... ]);
 653
 654                   'bin' has the intended executable file name
 655                   *without* extension, obj2bin is expected to add
 656                   that.  'objs' has the list of object files to build
 657                   this library.  'deps' has the list of library files
 658                   (also *without* extension) that the programs needs
 659                   to be linked with.
 660
 661     in2script   - function that produces build file lines to build a
 662                   script file from some input.
 663
 664                   called like this:
 665
 666                         in2script(script => "PATH/TO/scriptfile",
 667                                   sources => [ "PATH/TO/infile", ... ]);
 668
 669                   'script' has the intended script file name.
 670                   'sources' has the list of source files to build the
 671                   resulting script from.
 672
 673 In all cases, file file paths are relative to the build tree top, and
 674 the build file actions run with the build tree top as current working
 675 directory.
 676
 677 Make sure to end the section with these functions with a string that
 678 you thing is appropriate for the resulting build file.  If nothing
 679 else, end it like this:
 680
 681       "";       # Make sure no lingering values end up in the Makefile
 682     -}
 683
 684
 685 Configure helper scripts
 686 ========================
 687
 688 Configure uses helper scripts in this directory:
 689
 690 Checker scripts
 691 ---------------
 692
 693 These scripts are per platform family, to check the integrity of the
 694 tools used for configuration and building.  The checker script used is
 695 either {build_platform}-{build_file}-checker.pm or
 696 {build_platform}-checker.pm, where {build_platform} is the second
 697 'build_scheme' list element from the configuration target data, and
 698 {build_file} is 'build_file' from the same target data.
 699
 700 If the check succeeds, the script is expected to end with a non-zero
 701 expression.  If the check fails, the script can end with a zero, or
 702 with a `die`.