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