Configurations/README

   1 Configurations of OpenSSL target platforms
   2 ==========================================
   3
   4 Target configurations are a collection of facts that we know about
   5 different platforms and their capabilities.  We organise them in a
   6 hash table, where each entry represent a specific target.
   7
   8 In each table entry, the following keys are significant:
   9
  10         inherit_from    => Other targets to inherit values from.
  11                            Explained further below. [1]
  12         template        => Set to 1 if this isn't really a platform
  13                            target.  Instead, this target is a template
  14                            upon which other targets can be built.
  15                            Explained further below.  [1]
  16
  17         sys_id          => System identity for systems where that
  18                            is difficult to determine automatically.
  19
  20         cc              => The C compiler command, usually one of "cc",
  21                            "gcc" or "clang".  This command is normally
  22                            also used to link object files and
  23                            libraries into the final program.
  24         cxx             => The C++ compiler command, usually one of
  25                            "c++", "g++" or "clang++".  This command is
  26                            also used when linking a program where at
  27                            least one of the object file is made from
  28                            C++ source.
  29         cflags          => Flags that are used at all times when
  30                            compiling C object files.
  31         cxxflags        => Flags that are used at all times when
  32                            compiling C++ object files.  If unset, it
  33                            gets the same value as cflags.
  34         defines         => As an alternative, macro definitions may be
  35                            present here instead of in `cflags'.  If
  36                            given here, they MUST be as an array of the
  37                            string such as "MACRO=value", or just
  38                            "MACRO" for definitions without value.
  39         shared_cflag    => Extra compilation flags used when
  40                            compiling for shared libraries, typically
  41                            something like "-fPIC".
  42
  43         (linking is a complex thing, see [3] below)
  44         ld              => Linker command, usually not defined
  45                            (meaning the compiler command is used
  46                            instead).
  47                            (NOTE: this is here for future use, it's
  48                            not implemented yet)
  49         lflags          => Flags that are used when linking apps.
  50         shared_ldflag   => Flags that are used when linking shared
  51                            or dynamic libraries.
  52         plib_lflags     => Extra linking flags to appear just before
  53                            the libraries on the command line.
  54         ex_libs         => Extra libraries that are needed when
  55                            linking.
  56
  57         ar              => The library archive command, the default is
  58                            "ar".
  59                            (NOTE: this is here for future use, it's
  60                            not implemented yet)
  61         arflags         => Flags to be used with the library archive
  62                            command.
  63
  64         ranlib          => The library archive indexing command, the
  65                            default is 'ranlib' it it exists.
  66
  67         unistd          => An alternative header to the typical
  68                            '<unistd.h>'.  This is very rarely needed.
  69
  70         shared_extension => File name extension used for shared
  71                             libraries.
  72         obj_extension   => File name extension used for object files.
  73                            On unix, this defaults to ".o" (NOTE: this
  74                            is here for future use, it's not
  75                            implemented yet)
  76         exe_extension   => File name extension used for executable
  77                            files.  On unix, this defaults to "" (NOTE:
  78                            this is here for future use, it's not
  79                            implemented yet)
  80
  81         thread_scheme   => The type of threads is used on the
  82                            configured platform.  Currently known
  83                            values are "(unknown)", "pthreads",
  84                            "uithreads" (a.k.a solaris threads) and
  85                            "winthreads".  Except for "(unknown)", the
  86                            actual value is currently ignored but may
  87                            be used in the future.  See further notes
  88                            below [2].
  89         dso_scheme      => The type of dynamic shared objects to build
  90                            for.  This mostly comes into play with
  91                            engines, but can be used for other purposes
  92                            as well.  Valid values are "DLFCN"
  93                            (dlopen() et al), "DLFCN_NO_H" (for systems
  94                            that use dlopen() et al but do not have
  95                            fcntl.h), "DL" (shl_load() et al), "WIN32"
  96                            and "VMS".
  97         perlasm_scheme  => The perlasm method used to created the
  98                            assembler files used when compiling with
  99                            assembler implementations.
 100         shared_target   => The shared library building method used.
 101                            This is a target found in Makefile.shared.
 102         build_scheme    => The scheme used to build up a Makefile.
 103                            In its simplest form, the value is a string
 104                            with the name of the build scheme.
 105                            The value may also take the form of a list
 106                            of strings, if the build_scheme is to have
 107                            some options.  In this case, the first
 108                            string in the list is the name of the build
 109                            scheme.
 110                            Currently recognised build scheme is "unified".
 111                            For the "unified" build scheme, this item
 112                            *must* be an array with the first being the
 113                            word "unified" and the second being a word
 114                            to identify the platform family.
 115
 116         multilib        => On systems that support having multiple
 117                            implementations of a library (typically a
 118                            32-bit and a 64-bit variant), this is used
 119                            to have the different variants in different
 120                            directories.
 121
 122         bn_ops          => Building options (was just bignum options
 123                            in the earlier history of this option,
 124                            hence the name).  This a string of words
 125                            that describe properties on the designated
 126                            target platform, such as the type of
 127                            integers used to build up the bitnum,
 128                            different ways to implement certain ciphers
 129                            and so on.  To fully comprehend the
 130                            meaning, the best is to read the affected
 131                            source.
 132                            The valid words are:
 133
 134                            BN_LLONG     use 'unsigned long long' in
 135                                         some bignum calculations.
 136                                         This has no value when
 137                                         SIXTY_FOUR_BIT or
 138                                         SIXTY_FOUR_BIT_LONG is given.
 139                            RC4_CHAR     makes the basic RC4 unit of
 140                                         calculation an unsigned char.
 141                            SIXTY_FOUR_BIT       processor registers
 142                                                 are 64 bits, long is
 143                                                 32 bits, long long is
 144                                                 64 bits.
 145                            SIXTY_FOUR_BIT_LONG  processor registers
 146                                                 are 64 bits, long is
 147                                                 64 bits.
 148                            THIRTY_TWO_BIT       processor registers
 149                                                 are 32 bits.
 150                            EXPORT_VAR_AS_FN     for shared libraries,
 151                                                 export vars as
 152                                                 accessor functions.
 153
 154         apps_extra_src  => Extra source to build apps/openssl, as
 155                            needed by the target.
 156         cpuid_asm_src   => assembler implementation of cpuid code as
 157                            well as OPENSSL_cleanse().
 158                            Default to mem_clr.c
 159         bn_asm_src      => Assembler implementation of core bignum
 160                            functions.
 161                            Defaults to bn_asm.c
 162         ec_asm_src      => Assembler implementation of core EC
 163                            functions.
 164         des_asm_src     => Assembler implementation of core DES
 165                            encryption functions.
 166                            Defaults to 'des_enc.c fcrypt_b.c'
 167         aes_asm_src     => Assembler implementation of core AES
 168                            functions.
 169                            Defaults to 'aes_core.c aes_cbc.c'
 170         bf_asm_src      => Assembler implementation of core BlowFish
 171                            functions.
 172                            Defaults to 'bf_enc.c'
 173         md5_asm_src     => Assembler implementation of core MD5
 174                            functions.
 175         sha1_asm_src    => Assembler implementation of core SHA1,
 176                            functions, and also possibly SHA256 and
 177                            SHA512 ones.
 178         cast_asm_src    => Assembler implementation of core CAST
 179                            functions.
 180                            Defaults to 'c_enc.c'
 181         rc4_asm_src     => Assembler implementation of core RC4
 182                            functions.
 183                            Defaults to 'rc4_enc.c rc4_skey.c'
 184         rmd160_asm_src  => Assembler implementation of core RMD160
 185                            functions.
 186         rc5_asm_src     => Assembler implementation of core RC5
 187                            functions.
 188                            Defaults to 'rc5_enc.c'
 189         wp_asm_src      => Assembler implementation of core WHIRLPOOL
 190                            functions.
 191         cmll_asm_src    => Assembler implementation of core CAMELLIA
 192                            functions.
 193                            Defaults to 'camellia.c cmll_misc.c cmll_cbc.c'
 194         modes_asm_src   => Assembler implementation of cipher modes,
 195                            currently the functions gcm_gmult_4bit and
 196                            gcm_ghash_4bit.
 197         padlock_asm_src => Assembler implementation of core parts of
 198                            the padlock engine.  This is mandatory on
 199                            any platform where the padlock engine might
 200                            actually be built.
 201
 202
 203 [1] as part of the target configuration, one can have a key called
 204     'inherit_from' that indicate what other configurations to inherit
 205     data from.  These are resolved recursively.
 206
 207     Inheritance works as a set of default values that can be overridden
 208     by corresponding key values in the inheriting configuration.
 209
 210     Note 1: any configuration table can be used as a template.
 211     Note 2: pure templates have the attribute 'template => 1' and
 212             cannot be used as build targets.
 213
 214     If several configurations are given in the 'inherit_from' array,
 215     the values of same attribute are concatenated with space
 216     separation.  With this, it's possible to have several smaller
 217     templates for different configuration aspects that can be combined
 218     into a complete configuration.
 219
 220     instead of a scalar value or an array, a value can be a code block
 221     of the form 'sub { /* your code here */ }'.  This code block will
 222     be called with the list of inherited values for that key as
 223     arguments.  In fact, the concatenation of strings is really done
 224     by using 'sub { join(" ",@_) }' on the list of inherited values.
 225
 226     An example:
 227
 228         "foo" => {
 229                 template => 1,
 230                 haha => "ha ha",
 231                 hoho => "ho",
 232                 ignored => "This should not appear in the end result",
 233         },
 234         "bar" => {
 235                 template => 1,
 236                 haha => "ah",
 237                 hoho => "haho",
 238                 hehe => "hehe"
 239         },
 240         "laughter" => {
 241                 inherit_from => [ "foo", "bar" ],
 242                 hehe => sub { join(" ",(@_,"!!!")) },
 243                 ignored => "",
 244         }
 245
 246         The entry for "laughter" will become as follows after processing:
 247
 248         "laughter" => {
 249                 haha => "ha ha ah",
 250                 hoho => "ho haho",
 251                 hehe => "hehe !!!",
 252                 ignored => ""
 253         }
 254
 255 [2] OpenSSL is built with threading capabilities unless the user
 256     specifies 'no-threads'.  The value of the key 'thread_scheme' may
 257     be "(unknown)", in which case the user MUST give some compilation
 258     flags to Configure.
 259
 260 [3] OpenSSL has three types of things to link from object files or
 261     static libraries:
 262
 263     - shared libraries; that would be libcrypto and libssl.
 264     - shared objects (sometimes called dynamic libraries);  that would
 265       be the engines.
 266     - applications; those are apps/openssl and all the test apps.
 267
 268     Very roughly speaking, linking is done like this (words in braces
 269     represent the configuration settings documented at the beginning
 270     of this file):
 271
 272     shared libraries:
 273         {ld} $(CFLAGS) {shared_ldflag} -shared -o libfoo.so \
 274             -Wl,--whole-archive libfoo.a -Wl,--no-whole-archive \
 275             {plib_lflags} -lcrypto {ex_libs}
 276
 277     shared objects:
 278         {ld} $(CFLAGS) {shared_ldflag} -shared -o libeng.so \
 279             blah1.o blah2.o {plib_lflags} -lcrypto {ex_libs}
 280
 281     applications:
 282         {ld} $(CFLAGS) {lflags} -o app \
 283             app1.o utils.o {plib_lflags} -lssl -lcrypto {ex_libs}
 284
 285
 286 Historically, the target configurations came in form of a string with
 287 values separated by colons.  This use is deprecated.  The string form
 288 looked like this:
 289
 290    "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}"
 291
 292
 293 Build info files
 294 ================
 295
 296 The build.info files that are spread over the source tree contain the
 297 minimum information needed to build and distribute OpenSSL.  It uses a
 298 simple and yet fairly powerful language to determine what needs to be
 299 built, from what sources, and other relationships between files.
 300
 301 For every build.info file, all file references are relative to the
 302 directory of the build.info file for source files, and the
 303 corresponding build directory for built files if the build tree
 304 differs from the source tree.
 305
 306 When processed, every line is processed with the perl module
 307 Text::Template, using the delimiters "{-" and "-}".  The hashes
 308 %config and %target are passed to the perl fragments, along with
 309 $sourcedir and $builddir, which are the locations of the source
 310 directory for the current build.info file and the corresponding build
 311 directory, all relative to the top of the build tree.
 312
 313 To begin with, things to be built are declared by setting specific
 314 variables:
 315
 316     PROGRAMS=foo bar
 317     LIBS=libsomething
 318     ENGINES=libeng
 319     SCRIPTS=myhack
 320     EXTRA=file1 file2
 321
 322 Note that the files mentioned for PROGRAMS, LIBS and ENGINES *must* be
 323 without extensions.  The build file templates will figure them out.
 324
 325 For each thing to be built, it is then possible to say what sources
 326 they are built from:
 327
 328     PROGRAMS=foo bar
 329     SOURCE[foo]=foo.c common.c
 330     SOURCE[bar]=bar.c extra.c common.c
 331
 332 It's also possible to tell some other dependencies:
 333
 334     DEPEND[foo]=libsomething
 335     DEPEND[libbar]=libsomethingelse
 336
 337 (it could be argued that 'libsomething' and 'libsomethingelse' are
 338 source as well.  However, the files given through SOURCE are expected
 339 to be located in the source tree while files given through DEPEND are
 340 expected to be located in the build tree)
 341
 342 It's also possible to depend on static libraries explicitely:
 343
 344     DEPEND[foo]=libsomething.a
 345     DEPEND[libbar]=libsomethingelse.a
 346
 347 This should be rarely used, and care should be taken to make sure it's
 348 only used when supported.  For example, native Windows build doesn't
 349 support build static libraries and DLLs at the same time, so using
 350 static libraries on Windows can only be done when configured
 351 'no-shared'.
 352
 353 For some libraries, we maintain files with public symbols and their
 354 slot in a transfer vector (important on some platforms).  It can be
 355 declared like this:
 356
 357     ORDINALS[libcrypto]=crypto
 358
 359 The value is not the name of the file in question, but rather the
 360 argument to util/mkdef.pl that indicates which file to use.
 361
 362 One some platforms, shared libraries come with a name that's different
 363 from their static counterpart.  That's declared as follows:
 364
 365     SHARED_NAME[libfoo]=cygfoo-{- $config{shlibver} -}
 366
 367 The example is from Cygwin, which has a required naming convention.
 368
 369 Sometimes, it makes sense to rename an output file, for example a
 370 library:
 371
 372     RENAME[libfoo]=libbar
 373
 374 That lines has "libfoo" get renamed to "libbar".  While it makes no
 375 sense at all to just have a rename like that (why not just use
 376 "libbar" everywhere?), it does make sense when it can be used
 377 conditionally.  See a little further below for an example.
 378
 379 In some cases, it's desirable to include some source files in the
 380 shared form of a library only:
 381
 382     SHARED_SOURCE[libfoo]=dllmain.c
 383
 384 For any file to be built, it's also possible to tell what extra
 385 include paths the build of their source files should use:
 386
 387     INCLUDE[foo]=include
 388
 389 In some cases, one might want to generate some source files from
 390 others, that's done as follows:
 391
 392     GENERATE[foo.s]=asm/something.pl $(CFLAGS)
 393     GENERATE[bar.s]=asm/bar.S
 394
 395 The value of each GENERATE line is a command line or part of it.
 396 Configure places no rules on the command line, except the the first
 397 item muct be the generator file.  It is, however, entirely up to the
 398 build file template to define exactly how those command lines should
 399 be handled, how the output is captured and so on.
 400
 401 Sometimes, the generator file itself depends on other files, for
 402 example if it is a perl script that depends on other perl modules.
 403 This can be expressed using DEPEND like this:
 404
 405     DEPEND[asm/something.pl]=../perlasm/Foo.pm
 406
 407 There may also be cases where the exact file isn't easily specified,
 408 but an inclusion directory still needs to be specified.  INCLUDE can
 409 be used in that case:
 410
 411     INCLUDE[asm/something.pl]=../perlasm
 412
 413 NOTE: GENERATE lines are limited to one command only per GENERATE.
 414
 415 As a last resort, it's possible to have raw build file lines, between
 416 BEGINRAW and ENDRAW lines as follows:
 417
 418     BEGINRAW[Makefile(unix)]
 419     haha.h: {- $builddir -}/Makefile
 420         echo "/* haha */" > haha.h
 421     ENDRAW[Makefile(unix)]
 422
 423 The word within square brackets is the build_file configuration item
 424 or the build_file configuration item followed by the second word in the
 425 build_scheme configuration item for the configured target within
 426 parenthesis as shown above.  For example, with the following relevant
 427 configuration items:
 428
 429    build_file   => "build.ninja"
 430    build_scheme => [ "unified", "unix" ]
 431
 432 ... these lines will be considered:
 433
 434    BEGINRAW[build.ninja]
 435    build haha.h: echo "/* haha */" > haha.h
 436    ENDRAW[build.ninja]
 437
 438    BEGINRAW[build.ninja(unix)]
 439    build hoho.h: echo "/* hoho */" > hoho.h
 440    ENDRAW[build.ninja(unix)]
 441
 442 Should it be needed because the recipes within a RAW section might
 443 clash with those generated by Configure, it's possible to tell it
 444 not to generate them with the use of OVERRIDES, for example:
 445
 446     SOURCE[libfoo]=foo.c bar.c
 447
 448     OVERRIDES=bar.o
 449     BEGINRAW[Makefile(unix)]
 450     bar.o: bar.c
 451         $(CC) $(CFLAGS) -DSPECIAL -c -o $@ $<
 452     ENDRAW[Makefile(unix)]
 453
 454 See the documentation further up for more information on configuration
 455 items.
 456
 457 Finally, you can have some simple conditional use of the build.info
 458 information, looking like this:
 459
 460     IF[1]
 461      something
 462     ELSIF[2]
 463      something other
 464     ELSE
 465      something else
 466     ENDIF
 467
 468 The expression in square brackets is interpreted as a string in perl,
 469 and will be seen as true if perl thinks it is, otherwise false.  For
 470 example, the above would have "something" used, since 1 is true.
 471
 472 Together with the use of Text::Template, this can be used as
 473 conditions based on something in the passed variables, for example:
 474
 475     IF[{- $disabled{shared} -}]
 476       LIBS=libcrypto
 477       SOURCE[libcrypto]=...
 478     ELSE
 479       LIBS=libfoo
 480       SOURCE[libfoo]=...
 481     ENDIF
 482
 483 or:
 484
 485     # VMS has a cultural standard where all libraries are prefixed.
 486     # For OpenSSL, the choice is 'ossl_'
 487     IF[{- $config{target} =~ /^vms/ -}]
 488      RENAME[libcrypto]=ossl_libcrypto
 489      RENAME[libssl]=ossl_libssl
 490     ENDIF
 491
 492
 493 Build-file programming with the "unified" build system
 494 ======================================================
 495
 496 "Build files" are called "Makefile" on Unix-like operating systems,
 497 "descrip.mms" for MMS on VMS, "makefile" for nmake on Windows, etc.
 498
 499 To use the "unified" build system, the target configuration needs to
 500 set the three items 'build_scheme', 'build_file' and 'build_command'.
 501 In the rest of this section, we will assume that 'build_scheme' is set
 502 to "unified" (see the configurations documentation above for the
 503 details).
 504
 505 For any name given by 'build_file', the "unified" system expects a
 506 template file in Configurations/ named like the build file, with
 507 ".tmpl" appended, or in case of possible ambiguity, a combination of
 508 the second 'build_scheme' list item and the 'build_file' name.  For
 509 example, if 'build_file' is set to "Makefile", the template could be
 510 Configurations/Makefile.tmpl or Configurations/unix-Makefile.tmpl.
 511 In case both Configurations/unix-Makefile.tmpl and
 512 Configurations/Makefile.tmpl are present, the former takes
 513 precedence.
 514
 515 The build-file template is processed with the perl module
 516 Text::Template, using "{-" and "-}" as delimiters that enclose the
 517 perl code fragments that generate configuration-dependent content.
 518 Those perl fragments have access to all the hash variables from
 519 configdata.pem.
 520
 521 The build-file template is expected to define at least the following
 522 perl functions in a perl code fragment enclosed with "{-" and "-}".
 523 They are all expected to return a string with the lines they produce.
 524
 525     generatesrc - function that produces build file lines to generate
 526                   a source file from some input.
 527
 528                   It's called like this:
 529
 530                         generatesrc(src => "PATH/TO/tobegenerated",
 531                                     generator => [ "generatingfile", ... ]
 532                                     generator_incs => [ "INCL/PATH", ... ]
 533                                     generator_deps => [ "dep1", ... ]
 534                                     generator => [ "generatingfile", ... ]
 535                                     incs => [ "INCL/PATH", ... ],
 536                                     deps => [ "dep1", ... ],
 537                                     intent => one of "libs", "dso", "bin" );
 538
 539                   'src' has the name of the file to be generated.
 540                   'generator' is the command or part of command to
 541                   generate the file, of which the first item is
 542                   expected to be the file to generate from.
 543                   generatesrc() is expected to analyse and figure out
 544                   exactly how to apply that file and how to capture
 545                   the result.  'generator_incs' and 'generator_deps'
 546                   are include directories and files that the generator
 547                   file itself depends on.  'incs' and 'deps' are
 548                   include directories and files that are used if $(CC)
 549                   is used as an intermediary step when generating the
 550                   end product (the file indicated by 'src').  'intent'
 551                   indicates what the generated file is going to be
 552                   used for.
 553
 554     src2obj     - function that produces build file lines to build an
 555                   object file from source files and associated data.
 556
 557                   It's called like this:
 558
 559                         src2obj(obj => "PATH/TO/objectfile",
 560                                 srcs => [ "PATH/TO/sourcefile", ... ],
 561                                 deps => [ "dep1", ... ],
 562                                 incs => [ "INCL/PATH", ... ]
 563                                 intent => one of "lib", "dso", "bin" );
 564
 565                   'obj' has the intended object file *without*
 566                   extension, src2obj() is expected to add that.
 567                   'srcs' has the list of source files to build the
 568                   object file, with the first item being the source
 569                   file that directly corresponds to the object file.
 570                   'deps' is a list of explicit dependencies.  'incs'
 571                   is a list of include file directories.  Finally,
 572                   'intent' indicates what this object file is going
 573                   to be used for.
 574
 575     obj2lib     - function that produces build file lines to build a
 576                   static library file ("libfoo.a" in Unix terms) from
 577                   object files.
 578
 579                   called like this:
 580
 581                         obj2lib(lib => "PATH/TO/libfile",
 582                                 objs => [ "PATH/TO/objectfile", ... ]);
 583
 584                   'lib' has the intended library file name *without*
 585                   extension, obj2lib is expected to add that.  'objs'
 586                   has the list of object files (also *without*
 587                   extension) to build this library.
 588
 589     libobj2shlib - function that produces build file lines to build a
 590                   shareable object library file ("libfoo.so" in Unix
 591                   terms) from the corresponding static library file
 592                   or object files.
 593
 594                   called like this:
 595
 596                         libobj2shlib(shlib => "PATH/TO/shlibfile",
 597                                      lib => "PATH/TO/libfile",
 598                                      objs => [ "PATH/TO/objectfile", ... ],
 599                                      deps => [ "PATH/TO/otherlibfile", ... ],
 600                                      ordinals => [ "word", "/PATH/TO/ordfile" ]);
 601
 602                   'lib' has the intended library file name *without*
 603                   extension, libobj2shlib is expected to add that.
 604                   'shlib' has the corresponding shared library name
 605                   *without* extension.  'deps' has the list of other
 606                   libraries (also *without* extension) this library
 607                   needs to be linked with.  'objs' has the list of
 608                   object files (also *without* extension) to build
 609                   this library.  'ordinals' MAY be present, and when
 610                   it is, its value is an array where the word is
 611                   "crypto" or "ssl" and the file is one of the ordinal
 612                   files util/libeay.num or util/ssleay.num in the
 613                   source directory.
 614
 615                   This function has a choice; it can use the
 616                   corresponding static library as input to make the
 617                   shared library, or the list of object files.
 618
 619     obj2dso     - function that produces build file lines to build a
 620                   dynamic shared object file from object files.
 621
 622                   called like this:
 623
 624                         obj2dso(lib => "PATH/TO/libfile",
 625                                 objs => [ "PATH/TO/objectfile", ... ],
 626                                 deps => [ "PATH/TO/otherlibfile",
 627                                 ... ]);
 628
 629                   This is almost the same as libobj2shlib, but the
 630                   intent is to build a shareable library that can be
 631                   loaded in runtime (a "plugin"...).  The differences
 632                   are subtle, one of the most visible ones is that the
 633                   resulting shareable library is produced from object
 634                   files only.
 635
 636     obj2bin     - function that produces build file lines to build an
 637                   executable file from object files.
 638
 639                   called like this:
 640
 641                         obj2bin(bin => "PATH/TO/binfile",
 642                                 objs => [ "PATH/TO/objectfile", ... ],
 643                                 deps => [ "PATH/TO/libfile", ... ]);
 644
 645                   'bin' has the intended executable file name
 646                   *without* extension, obj2bin is expected to add
 647                   that.  'objs' has the list of object files (also
 648                   *without* extension) to build this library.  'deps'
 649                   has the list of library files (also *without*
 650                   extension) that the programs needs to be linked
 651                   with.
 652
 653     in2script   - function that produces build file lines to build a
 654                   script file from some input.
 655
 656                   called like this:
 657
 658                         in2script(script => "PATH/TO/scriptfile",
 659                                   sources => [ "PATH/TO/infile", ... ]);
 660
 661                   'script' has the intended script file name.
 662                   'sources' has the list of source files to build the
 663                   resulting script from.
 664
 665 In all cases, file file paths are relative to the build tree top, and
 666 the build file actions run with the build tree top as current working
 667 directory.
 668
 669 Make sure to end the section with these functions with a string that
 670 you thing is appropriate for the resulting build file.  If nothing
 671 else, end it like this:
 672
 673       "";       # Make sure no lingering values end up in the Makefile
 674     -}