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         uplink_arch     => The architecture to be used for compiling uplink
 169                            source.  This acts as a selector in build.info files.
 170                            This is separate from asm_arch because it's compiled
 171                            even when 'no-asm' is given, even though it contains
 172                            assembler source.
 173         perlasm_scheme  => The perlasm method used to create the
 174                            assembler files used when compiling with
 175                            assembler implementations.
 176         shared_target   => The shared library building method used.
 177                            This serves multiple purposes:
 178                            - as index for targets found in shared_info.pl.
 179                            - as linker script generation selector.
 180                            To serve both purposes, the index for shared_info.pl
 181                            should end with '-shared', and this suffix will be
 182                            removed for use as a linker script generation
 183                            selector.  Note that the latter is only used if
 184                            'shared_defflag' is defined.
 185         build_scheme    => The scheme used to build up a Makefile.
 186                            In its simplest form, the value is a string
 187                            with the name of the build scheme.
 188                            The value may also take the form of a list
 189                            of strings, if the build_scheme is to have
 190                            some options.  In this case, the first
 191                            string in the list is the name of the build
 192                            scheme.
 193                            Currently recognised build scheme is "unified".
 194                            For the "unified" build scheme, this item
 195                            *must* be an array with the first being the
 196                            word "unified" and the second being a word
 197                            to identify the platform family.
 198
 199         multilib        => On systems that support having multiple
 200                            implementations of a library (typically a
 201                            32-bit and a 64-bit variant), this is used
 202                            to have the different variants in different
 203                            directories.
 204
 205         bn_ops          => Building options (was just bignum options in
 206                            the earlier history of this option, hence the
 207                            name). This is a string of words that describe
 208                            algorithms' implementation parameters that
 209                            are optimal for the designated target platform,
 210                            such as the type of integers used to build up
 211                            the bignum, different ways to implement certain
 212                            ciphers and so on. To fully comprehend the
 213                            meaning, the best is to read the affected
 214                            source.
 215                            The valid words are:
 216
 217                            THIRTY_TWO_BIT       bignum limbs are 32 bits,
 218                                                 this is default if no
 219                                                 option is specified, it
 220                                                 works on any supported
 221                                                 system [unless "wider"
 222                                                 limb size is implied in
 223                                                 assembly code];
 224                            BN_LLONG             bignum limbs are 32 bits,
 225                                                 but 64-bit 'unsigned long
 226                                                 long' is used internally
 227                                                 in calculations;
 228                            SIXTY_FOUR_BIT_LONG  bignum limbs are 64 bits
 229                                                 and sizeof(long) is 8;
 230                            SIXTY_FOUR_BIT       bignums limbs are 64 bits,
 231                                                 but execution environment
 232                                                 is ILP32;
 233                            RC4_CHAR             RC4 key schedule is made
 234                                                 up of 'unsigned char's;
 235                            RC4_INT              RC4 key schedule is made
 236                                                 up of 'unsigned int's;
 237                            EXPORT_VAR_AS_FN     for shared libraries,
 238                                                 export vars as
 239                                                 accessor functions.
 240
 241         apps_aux_src    => Extra source to build apps/openssl and other
 242                            apps, as needed by the target and that can be
 243                            collected in a library.
 244         apps_init_src   => Init source to build apps/openssl and other
 245                            apps, as needed by the target.  This code
 246                            cannot be placed in a library, as the rest
 247                            of the code isn't expected to link to it
 248                            explicitly.
 249         cpuid_asm_src   => assembler implementation of cpuid code as
 250                            well as OPENSSL_cleanse().
 251                            Default to mem_clr.c
 252         bn_asm_src      => Assembler implementation of core bignum
 253                            functions.
 254                            Defaults to bn_asm.c
 255         ec_asm_src      => Assembler implementation of core EC
 256                            functions.
 257         des_asm_src     => Assembler implementation of core DES
 258                            encryption functions.
 259                            Defaults to 'des_enc.c fcrypt_b.c'
 260         aes_asm_src     => Assembler implementation of core AES
 261                            functions.
 262                            Defaults to 'aes_core.c aes_cbc.c'
 263         bf_asm_src      => Assembler implementation of core BlowFish
 264                            functions.
 265                            Defaults to 'bf_enc.c'
 266         md5_asm_src     => Assembler implementation of core MD5
 267                            functions.
 268         sha1_asm_src    => Assembler implementation of core SHA1,
 269                            functions, and also possibly SHA256 and
 270                            SHA512 ones.
 271         cast_asm_src    => Assembler implementation of core CAST
 272                            functions.
 273                            Defaults to 'c_enc.c'
 274         rc4_asm_src     => Assembler implementation of core RC4
 275                            functions.
 276                            Defaults to 'rc4_enc.c rc4_skey.c'
 277         rmd160_asm_src  => Assembler implementation of core RMD160
 278                            functions.
 279         rc5_asm_src     => Assembler implementation of core RC5
 280                            functions.
 281                            Defaults to 'rc5_enc.c'
 282         wp_asm_src      => Assembler implementation of core WHIRLPOOL
 283                            functions.
 284         cmll_asm_src    => Assembler implementation of core CAMELLIA
 285                            functions.
 286                            Defaults to 'camellia.c cmll_misc.c cmll_cbc.c'
 287         modes_asm_src   => Assembler implementation of cipher modes,
 288                            currently the functions gcm_gmult_4bit and
 289                            gcm_ghash_4bit.
 290         padlock_asm_src => Assembler implementation of core parts of
 291                            the padlock engine.  This is mandatory on
 292                            any platform where the padlock engine might
 293                            actually be built.
 294
 295
 296 [1] as part of the target configuration, one can have a key called
 297     'inherit_from' that indicate what other configurations to inherit
 298     data from.  These are resolved recursively.
 299
 300     Inheritance works as a set of default values that can be overridden
 301     by corresponding key values in the inheriting configuration.
 302
 303     Note 1: any configuration table can be used as a template.
 304     Note 2: pure templates have the attribute 'template => 1' and
 305             cannot be used as build targets.
 306
 307     If several configurations are given in the 'inherit_from' array,
 308     the values of same attribute are concatenated with space
 309     separation.  With this, it's possible to have several smaller
 310     templates for different configuration aspects that can be combined
 311     into a complete configuration.
 312
 313     instead of a scalar value or an array, a value can be a code block
 314     of the form 'sub { /* your code here */ }'.  This code block will
 315     be called with the list of inherited values for that key as
 316     arguments.  In fact, the concatenation of strings is really done
 317     by using 'sub { join(" ",@_) }' on the list of inherited values.
 318
 319     An example:
 320
 321         "foo" => {
 322                 template => 1,
 323                 haha => "ha ha",
 324                 hoho => "ho",
 325                 ignored => "This should not appear in the end result",
 326         },
 327         "bar" => {
 328                 template => 1,
 329                 haha => "ah",
 330                 hoho => "haho",
 331                 hehe => "hehe"
 332         },
 333         "laughter" => {
 334                 inherit_from => [ "foo", "bar" ],
 335                 hehe => sub { join(" ",(@_,"!!!")) },
 336                 ignored => "",
 337         }
 338
 339         The entry for "laughter" will become as follows after processing:
 340
 341         "laughter" => {
 342                 haha => "ha ha ah",
 343                 hoho => "ho haho",
 344                 hehe => "hehe !!!",
 345                 ignored => ""
 346         }
 347
 348 [2] OpenSSL is built with threading capabilities unless the user
 349     specifies 'no-threads'.  The value of the key 'thread_scheme' may
 350     be "(unknown)", in which case the user MUST give some compilation
 351     flags to Configure.
 352
 353 [3] OpenSSL has three types of things to link from object files or
 354     static libraries:
 355
 356     - shared libraries; that would be libcrypto and libssl.
 357     - shared objects (sometimes called dynamic libraries);  that would
 358       be the modules.
 359     - applications; those are apps/openssl and all the test apps.
 360
 361     Very roughly speaking, linking is done like this (words in braces
 362     represent the configuration settings documented at the beginning
 363     of this file):
 364
 365     shared libraries:
 366         {ld} $(CFLAGS) {lflags} {shared_ldflag} -o libfoo.so \
 367             foo/something.o foo/somethingelse.o {ex_libs}
 368
 369     shared objects:
 370         {ld} $(CFLAGS) {lflags} {module_ldflags} -o libeng.so \
 371             blah1.o blah2.o -lcrypto {ex_libs}
 372
 373     applications:
 374         {ld} $(CFLAGS) {lflags} -o app \
 375             app1.o utils.o -lssl -lcrypto {ex_libs}
 376
 377 [4] There are variants of these attribute, prefixed with `lib_',
 378     `dso_' or `bin_'.  Those variants replace the unprefixed attribute
 379     when building library, DSO or program modules specifically.
 380
 381 Historically, the target configurations came in form of a string with
 382 values separated by colons.  This use is deprecated.  The string form
 383 looked like this:
 384
 385    "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}"
 386
 387
 388 Build info files
 389 ================
 390
 391 The build.info files that are spread over the source tree contain the
 392 minimum information needed to build and distribute OpenSSL.  It uses a
 393 simple and yet fairly powerful language to determine what needs to be
 394 built, from what sources, and other relationships between files.
 395
 396 For every build.info file, all file references are relative to the
 397 directory of the build.info file for source files, and the
 398 corresponding build directory for built files if the build tree
 399 differs from the source tree.
 400
 401 When processed, every line is processed with the perl module
 402 Text::Template, using the delimiters "{-" and "-}".  The hashes
 403 %config and %target are passed to the perl fragments, along with
 404 $sourcedir and $builddir, which are the locations of the source
 405 directory for the current build.info file and the corresponding build
 406 directory, all relative to the top of the build tree.
 407
 408 'Configure' only knows inherently about the top build.info file.  For
 409 any other directory that has one, further directories to look into
 410 must be indicated like this:
 411
 412     SUBDIRS=something someelse
 413
 414 On to things to be built; they are declared by setting specific
 415 variables:
 416
 417     PROGRAMS=foo bar
 418     LIBS=libsomething
 419     MODULES=libeng
 420     SCRIPTS=myhack
 421
 422 Note that the files mentioned for PROGRAMS, LIBS and MODULES *must* be
 423 without extensions.  The build file templates will figure them out.
 424
 425 For each thing to be built, it is then possible to say what sources
 426 they are built from:
 427
 428     PROGRAMS=foo bar
 429     SOURCE[foo]=foo.c common.c
 430     SOURCE[bar]=bar.c extra.c common.c
 431
 432 It's also possible to tell some other dependencies:
 433
 434     DEPEND[foo]=libsomething
 435     DEPEND[libbar]=libsomethingelse
 436
 437 (it could be argued that 'libsomething' and 'libsomethingelse' are
 438 source as well.  However, the files given through SOURCE are expected
 439 to be located in the source tree while files given through DEPEND are
 440 expected to be located in the build tree)
 441
 442 It's also possible to depend on static libraries explicitly:
 443
 444     DEPEND[foo]=libsomething.a
 445     DEPEND[libbar]=libsomethingelse.a
 446
 447 This should be rarely used, and care should be taken to make sure it's
 448 only used when supported.  For example, native Windows build doesn't
 449 support building static libraries and DLLs at the same time, so using
 450 static libraries on Windows can only be done when configured
 451 'no-shared'.
 452
 453 In some cases, it's desirable to include some source files in the
 454 shared form of a library only:
 455
 456     SHARED_SOURCE[libfoo]=dllmain.c
 457
 458 For any file to be built, it's also possible to tell what extra
 459 include paths the build of their source files should use:
 460
 461     INCLUDE[foo]=include
 462
 463 It's also possible to specify C macros that should be defined:
 464
 465     DEFINE[foo]=FOO BAR=1
 466
 467 In some cases, one might want to generate some source files from
 468 others, that's done as follows:
 469
 470     GENERATE[foo.s]=asm/something.pl $(CFLAGS)
 471     GENERATE[bar.s]=asm/bar.S
 472
 473 The value of each GENERATE line is a command line or part of it.
 474 Configure places no rules on the command line, except that the first
 475 item must be the generator file.  It is, however, entirely up to the
 476 build file template to define exactly how those command lines should
 477 be handled, how the output is captured and so on.
 478
 479 Sometimes, the generator file itself depends on other files, for
 480 example if it is a perl script that depends on other perl modules.
 481 This can be expressed using DEPEND like this:
 482
 483     DEPEND[asm/something.pl]=../perlasm/Foo.pm
 484
 485 There may also be cases where the exact file isn't easily specified,
 486 but an inclusion directory still needs to be specified.  INCLUDE can
 487 be used in that case:
 488
 489     INCLUDE[asm/something.pl]=../perlasm
 490
 491 NOTE: GENERATE lines are limited to one command only per GENERATE.
 492
 493 Finally, you can have some simple conditional use of the build.info
 494 information, looking like this:
 495
 496     IF[1]
 497      something
 498     ELSIF[2]
 499      something other
 500     ELSE
 501      something else
 502     ENDIF
 503
 504 The expression in square brackets is interpreted as a string in perl,
 505 and will be seen as true if perl thinks it is, otherwise false.  For
 506 example, the above would have "something" used, since 1 is true.
 507
 508 Together with the use of Text::Template, this can be used as
 509 conditions based on something in the passed variables, for example:
 510
 511     IF[{- $disabled{shared} -}]
 512       LIBS=libcrypto
 513       SOURCE[libcrypto]=...
 514     ELSE
 515       LIBS=libfoo
 516       SOURCE[libfoo]=...
 517     ENDIF
 518
 519
 520 Build-file programming with the "unified" build system
 521 ======================================================
 522
 523 "Build files" are called "Makefile" on Unix-like operating systems,
 524 "descrip.mms" for MMS on VMS, "makefile" for nmake on Windows, etc.
 525
 526 To use the "unified" build system, the target configuration needs to
 527 set the three items 'build_scheme', 'build_file' and 'build_command'.
 528 In the rest of this section, we will assume that 'build_scheme' is set
 529 to "unified" (see the configurations documentation above for the
 530 details).
 531
 532 For any name given by 'build_file', the "unified" system expects a
 533 template file in Configurations/ named like the build file, with
 534 ".tmpl" appended, or in case of possible ambiguity, a combination of
 535 the second 'build_scheme' list item and the 'build_file' name.  For
 536 example, if 'build_file' is set to "Makefile", the template could be
 537 Configurations/Makefile.tmpl or Configurations/unix-Makefile.tmpl.
 538 In case both Configurations/unix-Makefile.tmpl and
 539 Configurations/Makefile.tmpl are present, the former takes
 540 precedence.
 541
 542 The build-file template is processed with the perl module
 543 Text::Template, using "{-" and "-}" as delimiters that enclose the
 544 perl code fragments that generate configuration-dependent content.
 545 Those perl fragments have access to all the hash variables from
 546 configdata.pem.
 547
 548 The build-file template is expected to define at least the following
 549 perl functions in a perl code fragment enclosed with "{-" and "-}".
 550 They are all expected to return a string with the lines they produce.
 551
 552     generatesrc - function that produces build file lines to generate
 553                   a source file from some input.
 554
 555                   It's called like this:
 556
 557                         generatesrc(src => "PATH/TO/tobegenerated",
 558                                     generator => [ "generatingfile", ... ]
 559                                     generator_incs => [ "INCL/PATH", ... ]
 560                                     generator_deps => [ "dep1", ... ]
 561                                     generator => [ "generatingfile", ... ]
 562                                     incs => [ "INCL/PATH", ... ],
 563                                     deps => [ "dep1", ... ],
 564                                     intent => one of "libs", "dso", "bin" );
 565
 566                   'src' has the name of the file to be generated.
 567                   'generator' is the command or part of command to
 568                   generate the file, of which the first item is
 569                   expected to be the file to generate from.
 570                   generatesrc() is expected to analyse and figure out
 571                   exactly how to apply that file and how to capture
 572                   the result.  'generator_incs' and 'generator_deps'
 573                   are include directories and files that the generator
 574                   file itself depends on.  'incs' and 'deps' are
 575                   include directories and files that are used if $(CC)
 576                   is used as an intermediary step when generating the
 577                   end product (the file indicated by 'src').  'intent'
 578                   indicates what the generated file is going to be
 579                   used for.
 580
 581     src2obj     - function that produces build file lines to build an
 582                   object file from source files and associated data.
 583
 584                   It's called like this:
 585
 586                         src2obj(obj => "PATH/TO/objectfile",
 587                                 srcs => [ "PATH/TO/sourcefile", ... ],
 588                                 deps => [ "dep1", ... ],
 589                                 incs => [ "INCL/PATH", ... ]
 590                                 intent => one of "lib", "dso", "bin" );
 591
 592                   'obj' has the intended object file with '.o'
 593                   extension, src2obj() is expected to change it to
 594                   something more suitable for the platform.
 595                   'srcs' has the list of source files to build the
 596                   object file, with the first item being the source
 597                   file that directly corresponds to the object file.
 598                   'deps' is a list of explicit dependencies.  'incs'
 599                   is a list of include file directories.  Finally,
 600                   'intent' indicates what this object file is going
 601                   to be used for.
 602
 603     obj2lib     - function that produces build file lines to build a
 604                   static library file ("libfoo.a" in Unix terms) from
 605                   object files.
 606
 607                   called like this:
 608
 609                         obj2lib(lib => "PATH/TO/libfile",
 610                                 objs => [ "PATH/TO/objectfile", ... ]);
 611
 612                   'lib' has the intended library file name *without*
 613                   extension, obj2lib is expected to add that.  'objs'
 614                   has the list of object files to build this library.
 615
 616     libobj2shlib - backward compatibility function that's used the
 617                   same way as obj2shlib (described next), and was
 618                   expected to build the shared library from the
 619                   corresponding static library when that was suitable.
 620                   NOTE: building a shared library from a static
 621                   library is now DEPRECATED, as they no longer share
 622                   object files.  Attempting to do this will fail.
 623
 624     obj2shlib   - function that produces build file lines to build a
 625                   shareable object library file ("libfoo.so" in Unix
 626                   terms) from the corresponding object files.
 627
 628                   called like this:
 629
 630                         obj2shlib(shlib => "PATH/TO/shlibfile",
 631                                   lib => "PATH/TO/libfile",
 632                                   objs => [ "PATH/TO/objectfile", ... ],
 633                                   deps => [ "PATH/TO/otherlibfile", ... ]);
 634
 635                   'lib' has the base (static) library ffile name
 636                   *without* extension.  This is useful in case
 637                   supporting files are needed (such as import
 638                   libraries on Windows).
 639                   'shlib' has the corresponding shared library name
 640                   *without* extension.  'deps' has the list of other
 641                   libraries (also *without* extension) this library
 642                   needs to be linked with.  'objs' has the list of
 643                   object files to build this library.
 644
 645     obj2dso     - function that produces build file lines to build a
 646                   dynamic shared object file from object files.
 647
 648                   called like this:
 649
 650                         obj2dso(lib => "PATH/TO/libfile",
 651                                 objs => [ "PATH/TO/objectfile", ... ],
 652                                 deps => [ "PATH/TO/otherlibfile",
 653                                 ... ]);
 654
 655                   This is almost the same as obj2shlib, but the
 656                   intent is to build a shareable library that can be
 657                   loaded in runtime (a "plugin"...).
 658
 659     obj2bin     - function that produces build file lines to build an
 660                   executable file from object files.
 661
 662                   called like this:
 663
 664                         obj2bin(bin => "PATH/TO/binfile",
 665                                 objs => [ "PATH/TO/objectfile", ... ],
 666                                 deps => [ "PATH/TO/libfile", ... ]);
 667
 668                   'bin' has the intended executable file name
 669                   *without* extension, obj2bin is expected to add
 670                   that.  'objs' has the list of object files to build
 671                   this library.  'deps' has the list of library files
 672                   (also *without* extension) that the programs needs
 673                   to be linked with.
 674
 675     in2script   - function that produces build file lines to build a
 676                   script file from some input.
 677
 678                   called like this:
 679
 680                         in2script(script => "PATH/TO/scriptfile",
 681                                   sources => [ "PATH/TO/infile", ... ]);
 682
 683                   'script' has the intended script file name.
 684                   'sources' has the list of source files to build the
 685                   resulting script from.
 686
 687 In all cases, file file paths are relative to the build tree top, and
 688 the build file actions run with the build tree top as current working
 689 directory.
 690
 691 Make sure to end the section with these functions with a string that
 692 you thing is appropriate for the resulting build file.  If nothing
 693 else, end it like this:
 694
 695       "";       # Make sure no lingering values end up in the Makefile
 696     -}
 697
 698
 699 Configure helper scripts
 700 ========================
 701
 702 Configure uses helper scripts in this directory:
 703
 704 Checker scripts
 705 ---------------
 706
 707 These scripts are per platform family, to check the integrity of the
 708 tools used for configuration and building.  The checker script used is
 709 either {build_platform}-{build_file}-checker.pm or
 710 {build_platform}-checker.pm, where {build_platform} is the second
 711 'build_scheme' list element from the configuration target data, and
 712 {build_file} is 'build_file' from the same target data.
 713
 714 If the check succeeds, the script is expected to end with a non-zero
 715 expression.  If the check fails, the script can end with a zero, or
 716 with a `die`.