1Intro
2=====
3
4This directory contains a few sets of files that are used for
5configuration 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
18Configurations of OpenSSL target platforms
19==========================================
20
21Configuration targets are a collection of facts that we know about
22different platforms and their capabilities.  We organise them in a
23hash table, where each entry represent a specific target.
24
25Note that configuration target names must be unique across all config
26files.  The Configure script does check that a config file doesn't
27have config targets that shadow config targets from other files.
28
29In 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                           engines, 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        perlasm_scheme  => The perlasm method used to create the
169                           assembler files used when compiling with
170                           assembler implementations.
171        shared_target   => The shared library building method used.
172                           This is a target found in Makefile.shared.
173        build_scheme    => The scheme used to build up a Makefile.
174                           In its simplest form, the value is a string
175                           with the name of the build scheme.
176                           The value may also take the form of a list
177                           of strings, if the build_scheme is to have
178                           some options.  In this case, the first
179                           string in the list is the name of the build
180                           scheme.
181                           Currently recognised build scheme is "unified".
182                           For the "unified" build scheme, this item
183                           *must* be an array with the first being the
184                           word "unified" and the second being a word
185                           to identify the platform family.
186
187        multilib        => On systems that support having multiple
188                           implementations of a library (typically a
189                           32-bit and a 64-bit variant), this is used
190                           to have the different variants in different
191                           directories.
192
193        bn_ops          => Building options (was just bignum options in
194                           the earlier history of this option, hence the
195                           name). This is a string of words that describe
196                           algorithms' implementation parameters that
197                           are optimal for the designated target platform,
198                           such as the type of integers used to build up
199                           the bignum, different ways to implement certain
200                           ciphers and so on. To fully comprehend the
201                           meaning, the best is to read the affected
202                           source.
203                           The valid words are:
204
205                           THIRTY_TWO_BIT       bignum limbs are 32 bits,
206                                                this is default if no
207                                                option is specified, it
208                                                works on any supported
209                                                system [unless "wider"
210                                                limb size is implied in
211                                                assembly code];
212                           BN_LLONG             bignum limbs are 32 bits,
213                                                but 64-bit 'unsigned long
214                                                long' is used internally
215                                                in calculations;
216                           SIXTY_FOUR_BIT_LONG  bignum limbs are 64 bits
217                                                and sizeof(long) is 8;
218                           SIXTY_FOUR_BIT       bignums limbs are 64 bits,
219                                                but execution environment
220                                                is ILP32;
221                           RC4_CHAR             RC4 key schedule is made
222                                                up of 'unsigned char's;
223                           RC4_INT              RC4 key schedule is made
224                                                up of 'unsigned int's;
225                           EXPORT_VAR_AS_FN     for shared libraries,
226                                                export vars as
227                                                accessor functions.
228
229        apps_aux_src    => Extra source to build apps/openssl and other
230                           apps, as needed by the target and that can be
231                           collected in a library.
232        apps_init_src   => Init source to build apps/openssl and other
233                           apps, as needed by the target.  This code
234                           cannot be placed in a library, as the rest
235                           of the code isn't expected to link to it
236                           explicitly.
237        cpuid_asm_src   => assembler implementation of cpuid code as
238                           well as OPENSSL_cleanse().
239                           Default to mem_clr.c
240        bn_asm_src      => Assembler implementation of core bignum
241                           functions.
242                           Defaults to bn_asm.c
243        ec_asm_src      => Assembler implementation of core EC
244                           functions.
245        des_asm_src     => Assembler implementation of core DES
246                           encryption functions.
247                           Defaults to 'des_enc.c fcrypt_b.c'
248        aes_asm_src     => Assembler implementation of core AES
249                           functions.
250                           Defaults to 'aes_core.c aes_cbc.c'
251        bf_asm_src      => Assembler implementation of core BlowFish
252                           functions.
253                           Defaults to 'bf_enc.c'
254        md5_asm_src     => Assembler implementation of core MD5
255                           functions.
256        sha1_asm_src    => Assembler implementation of core SHA1,
257                           functions, and also possibly SHA256 and
258                           SHA512 ones.
259        cast_asm_src    => Assembler implementation of core CAST
260                           functions.
261                           Defaults to 'c_enc.c'
262        rc4_asm_src     => Assembler implementation of core RC4
263                           functions.
264                           Defaults to 'rc4_enc.c rc4_skey.c'
265        rmd160_asm_src  => Assembler implementation of core RMD160
266                           functions.
267        rc5_asm_src     => Assembler implementation of core RC5
268                           functions.
269                           Defaults to 'rc5_enc.c'
270        wp_asm_src      => Assembler implementation of core WHIRLPOOL
271                           functions.
272        cmll_asm_src    => Assembler implementation of core CAMELLIA
273                           functions.
274                           Defaults to 'camellia.c cmll_misc.c cmll_cbc.c'
275        modes_asm_src   => Assembler implementation of cipher modes,
276                           currently the functions gcm_gmult_4bit and
277                           gcm_ghash_4bit.
278        padlock_asm_src => Assembler implementation of core parts of
279                           the padlock engine.  This is mandatory on
280                           any platform where the padlock engine might
281                           actually be built.
282
283
284[1] as part of the target configuration, one can have a key called
285    'inherit_from' that indicate what other configurations to inherit
286    data from.  These are resolved recursively.
287
288    Inheritance works as a set of default values that can be overridden
289    by corresponding key values in the inheriting configuration.
290
291    Note 1: any configuration table can be used as a template.
292    Note 2: pure templates have the attribute 'template => 1' and
293            cannot be used as build targets.
294
295    If several configurations are given in the 'inherit_from' array,
296    the values of same attribute are concatenated with space
297    separation.  With this, it's possible to have several smaller
298    templates for different configuration aspects that can be combined
299    into a complete configuration.
300
301    instead of a scalar value or an array, a value can be a code block
302    of the form 'sub { /* your code here */ }'.  This code block will
303    be called with the list of inherited values for that key as
304    arguments.  In fact, the concatenation of strings is really done
305    by using 'sub { join(" ",@_) }' on the list of inherited values.
306
307    An example:
308
309        "foo" => {
310                template => 1,
311                haha => "ha ha",
312                hoho => "ho",
313                ignored => "This should not appear in the end result",
314        },
315        "bar" => {
316                template => 1,
317                haha => "ah",
318                hoho => "haho",
319                hehe => "hehe"
320        },
321        "laughter" => {
322                inherit_from => [ "foo", "bar" ],
323                hehe => sub { join(" ",(@_,"!!!")) },
324                ignored => "",
325        }
326
327        The entry for "laughter" will become as follows after processing:
328
329        "laughter" => {
330                haha => "ha ha ah",
331                hoho => "ho haho",
332                hehe => "hehe !!!",
333                ignored => ""
334        }
335
336[2] OpenSSL is built with threading capabilities unless the user
337    specifies 'no-threads'.  The value of the key 'thread_scheme' may
338    be "(unknown)", in which case the user MUST give some compilation
339    flags to Configure.
340
341[3] OpenSSL has three types of things to link from object files or
342    static libraries:
343
344    - shared libraries; that would be libcrypto and libssl.
345    - shared objects (sometimes called dynamic libraries);  that would
346      be the engines.
347    - applications; those are apps/openssl and all the test apps.
348
349    Very roughly speaking, linking is done like this (words in braces
350    represent the configuration settings documented at the beginning
351    of this file):
352
353    shared libraries:
354        {ld} $(CFLAGS) {lflags} {shared_ldflag} -o libfoo.so \
355            foo/something.o foo/somethingelse.o {ex_libs}
356
357    shared objects:
358        {ld} $(CFLAGS) {lflags} {module_ldflags} -o libeng.so \
359            blah1.o blah2.o -lcrypto {ex_libs}
360
361    applications:
362        {ld} $(CFLAGS) {lflags} -o app \
363            app1.o utils.o -lssl -lcrypto {ex_libs}
364
365[4] There are variants of these attribute, prefixed with `lib_',
366    `dso_' or `bin_'.  Those variants replace the unprefixed attribute
367    when building library, DSO or program modules specifically.
368
369Historically, the target configurations came in form of a string with
370values separated by colons.  This use is deprecated.  The string form
371looked like this:
372
373   "target" => "{cc}:{cflags}:{unistd}:{thread_cflag}:{sys_id}:{lflags}:{bn_ops}:{cpuid_obj}:{bn_obj}:{ec_obj}:{des_obj}:{aes_obj}:{bf_obj}:{md5_obj}:{sha1_obj}:{cast_obj}:{rc4_obj}:{rmd160_obj}:{rc5_obj}:{wp_obj}:{cmll_obj}:{modes_obj}:{padlock_obj}:{perlasm_scheme}:{dso_scheme}:{shared_target}:{shared_cflag}:{shared_ldflag}:{shared_extension}:{ranlib}:{arflags}:{multilib}"
374
375
376Build info files
377================
378
379The build.info files that are spread over the source tree contain the
380minimum information needed to build and distribute OpenSSL.  It uses a
381simple and yet fairly powerful language to determine what needs to be
382built, from what sources, and other relationships between files.
383
384For every build.info file, all file references are relative to the
385directory of the build.info file for source files, and the
386corresponding build directory for built files if the build tree
387differs from the source tree.
388
389When processed, every line is processed with the perl module
390Text::Template, using the delimiters "{-" and "-}".  The hashes
391%config and %target are passed to the perl fragments, along with
392$sourcedir and $builddir, which are the locations of the source
393directory for the current build.info file and the corresponding build
394directory, all relative to the top of the build tree.
395
396To begin with, things to be built are declared by setting specific
397variables:
398
399    PROGRAMS=foo bar
400    LIBS=libsomething
401    ENGINES=libeng
402    SCRIPTS=myhack
403    EXTRA=file1 file2
404
405Note that the files mentioned for PROGRAMS, LIBS and ENGINES *must* be
406without extensions.  The build file templates will figure them out.
407
408For each thing to be built, it is then possible to say what sources
409they are built from:
410
411    PROGRAMS=foo bar
412    SOURCE[foo]=foo.c common.c
413    SOURCE[bar]=bar.c extra.c common.c
414
415It's also possible to tell some other dependencies:
416
417    DEPEND[foo]=libsomething
418    DEPEND[libbar]=libsomethingelse
419
420(it could be argued that 'libsomething' and 'libsomethingelse' are
421source as well.  However, the files given through SOURCE are expected
422to be located in the source tree while files given through DEPEND are
423expected to be located in the build tree)
424
425It's also possible to depend on static libraries explicitly:
426
427    DEPEND[foo]=libsomething.a
428    DEPEND[libbar]=libsomethingelse.a
429
430This should be rarely used, and care should be taken to make sure it's
431only used when supported.  For example, native Windows build doesn't
432support building static libraries and DLLs at the same time, so using
433static libraries on Windows can only be done when configured
434'no-shared'.
435
436One some platforms, shared libraries come with a name that's different
437from their static counterpart.  That's declared as follows:
438
439    SHARED_NAME[libfoo]=cygfoo-{- $config{shlibver} -}
440
441The example is from Cygwin, which has a required naming convention.
442
443Sometimes, it makes sense to rename an output file, for example a
444library:
445
446    RENAME[libfoo]=libbar
447
448That line has "libfoo" renamed to "libbar".  While it makes no
449sense at all to just have a rename like that (why not just use
450"libbar" everywhere?), it does make sense when it can be used
451conditionally.  See a little further below for an example.
452
453In some cases, it's desirable to include some source files in the
454shared form of a library only:
455
456    SHARED_SOURCE[libfoo]=dllmain.c
457
458For any file to be built, it's also possible to tell what extra
459include paths the build of their source files should use:
460
461    INCLUDE[foo]=include
462
463In some cases, one might want to generate some source files from
464others, that's done as follows:
465
466    GENERATE[foo.s]=asm/something.pl $(CFLAGS)
467    GENERATE[bar.s]=asm/bar.S
468
469The value of each GENERATE line is a command line or part of it.
470Configure places no rules on the command line, except that the first
471item must be the generator file.  It is, however, entirely up to the
472build file template to define exactly how those command lines should
473be handled, how the output is captured and so on.
474
475Sometimes, the generator file itself depends on other files, for
476example if it is a perl script that depends on other perl modules.
477This can be expressed using DEPEND like this:
478
479    DEPEND[asm/something.pl]=../perlasm/Foo.pm
480
481There may also be cases where the exact file isn't easily specified,
482but an inclusion directory still needs to be specified.  INCLUDE can
483be used in that case:
484
485    INCLUDE[asm/something.pl]=../perlasm
486
487NOTE: GENERATE lines are limited to one command only per GENERATE.
488
489As a last resort, it's possible to have raw build file lines, between
490BEGINRAW and ENDRAW lines as follows:
491
492    BEGINRAW[Makefile(unix)]
493    haha.h: {- $builddir -}/Makefile
494        echo "/* haha */" > haha.h
495    ENDRAW[Makefile(unix)]
496
497The word within square brackets is the build_file configuration item
498or the build_file configuration item followed by the second word in the
499build_scheme configuration item for the configured target within
500parenthesis as shown above.  For example, with the following relevant
501configuration items:
502
503   build_file   => "build.ninja"
504   build_scheme => [ "unified", "unix" ]
505
506... these lines will be considered:
507
508   BEGINRAW[build.ninja]
509   build haha.h: echo "/* haha */" > haha.h
510   ENDRAW[build.ninja]
511
512   BEGINRAW[build.ninja(unix)]
513   build hoho.h: echo "/* hoho */" > hoho.h
514   ENDRAW[build.ninja(unix)]
515
516Should it be needed because the recipes within a RAW section might
517clash with those generated by Configure, it's possible to tell it
518not to generate them with the use of OVERRIDES, for example:
519
520    SOURCE[libfoo]=foo.c bar.c
521
522    OVERRIDES=bar.o
523    BEGINRAW[Makefile(unix)]
524    bar.o: bar.c
525    	$(CC) $(CFLAGS) -DSPECIAL -c -o $@ $<
526    ENDRAW[Makefile(unix)]
527
528See the documentation further up for more information on configuration
529items.
530
531Finally, you can have some simple conditional use of the build.info
532information, looking like this:
533
534    IF[1]
535     something
536    ELSIF[2]
537     something other
538    ELSE
539     something else
540    ENDIF
541
542The expression in square brackets is interpreted as a string in perl,
543and will be seen as true if perl thinks it is, otherwise false.  For
544example, the above would have "something" used, since 1 is true.
545
546Together with the use of Text::Template, this can be used as
547conditions based on something in the passed variables, for example:
548
549    IF[{- $disabled{shared} -}]
550      LIBS=libcrypto
551      SOURCE[libcrypto]=...
552    ELSE
553      LIBS=libfoo
554      SOURCE[libfoo]=...
555    ENDIF
556
557or:
558
559    # VMS has a cultural standard where all libraries are prefixed.
560    # For OpenSSL, the choice is 'ossl_'
561    IF[{- $config{target} =~ /^vms/ -}]
562     RENAME[libcrypto]=ossl_libcrypto
563     RENAME[libssl]=ossl_libssl
564    ENDIF
565
566
567Build-file programming with the "unified" build system
568======================================================
569
570"Build files" are called "Makefile" on Unix-like operating systems,
571"descrip.mms" for MMS on VMS, "makefile" for nmake on Windows, etc.
572
573To use the "unified" build system, the target configuration needs to
574set the three items 'build_scheme', 'build_file' and 'build_command'.
575In the rest of this section, we will assume that 'build_scheme' is set
576to "unified" (see the configurations documentation above for the
577details).
578
579For any name given by 'build_file', the "unified" system expects a
580template file in Configurations/ named like the build file, with
581".tmpl" appended, or in case of possible ambiguity, a combination of
582the second 'build_scheme' list item and the 'build_file' name.  For
583example, if 'build_file' is set to "Makefile", the template could be
584Configurations/Makefile.tmpl or Configurations/unix-Makefile.tmpl.
585In case both Configurations/unix-Makefile.tmpl and
586Configurations/Makefile.tmpl are present, the former takes
587precedence.
588
589The build-file template is processed with the perl module
590Text::Template, using "{-" and "-}" as delimiters that enclose the
591perl code fragments that generate configuration-dependent content.
592Those perl fragments have access to all the hash variables from
593configdata.pem.
594
595The build-file template is expected to define at least the following
596perl functions in a perl code fragment enclosed with "{-" and "-}".
597They are all expected to return a string with the lines they produce.
598
599    generatesrc - function that produces build file lines to generate
600                  a source file from some input.
601
602                  It's called like this:
603
604                        generatesrc(src => "PATH/TO/tobegenerated",
605                                    generator => [ "generatingfile", ... ]
606                                    generator_incs => [ "INCL/PATH", ... ]
607                                    generator_deps => [ "dep1", ... ]
608                                    generator => [ "generatingfile", ... ]
609                                    incs => [ "INCL/PATH", ... ],
610                                    deps => [ "dep1", ... ],
611                                    intent => one of "libs", "dso", "bin" );
612
613                  'src' has the name of the file to be generated.
614                  'generator' is the command or part of command to
615                  generate the file, of which the first item is
616                  expected to be the file to generate from.
617                  generatesrc() is expected to analyse and figure out
618                  exactly how to apply that file and how to capture
619                  the result.  'generator_incs' and 'generator_deps'
620                  are include directories and files that the generator
621                  file itself depends on.  'incs' and 'deps' are
622                  include directories and files that are used if $(CC)
623                  is used as an intermediary step when generating the
624                  end product (the file indicated by 'src').  'intent'
625                  indicates what the generated file is going to be
626                  used for.
627
628    src2obj     - function that produces build file lines to build an
629                  object file from source files and associated data.
630
631                  It's called like this:
632
633                        src2obj(obj => "PATH/TO/objectfile",
634                                srcs => [ "PATH/TO/sourcefile", ... ],
635                                deps => [ "dep1", ... ],
636                                incs => [ "INCL/PATH", ... ]
637                                intent => one of "lib", "dso", "bin" );
638
639                  'obj' has the intended object file *without*
640                  extension, src2obj() is expected to add that.
641                  'srcs' has the list of source files to build the
642                  object file, with the first item being the source
643                  file that directly corresponds to the object file.
644                  'deps' is a list of explicit dependencies.  'incs'
645                  is a list of include file directories.  Finally,
646                  'intent' indicates what this object file is going
647                  to be used for.
648
649    obj2lib     - function that produces build file lines to build a
650                  static library file ("libfoo.a" in Unix terms) from
651                  object files.
652
653                  called like this:
654
655                        obj2lib(lib => "PATH/TO/libfile",
656                                objs => [ "PATH/TO/objectfile", ... ]);
657
658                  'lib' has the intended library file name *without*
659                  extension, obj2lib is expected to add that.  'objs'
660                  has the list of object files (also *without*
661                  extension) to build this library.
662
663    libobj2shlib - function that produces build file lines to build a
664                  shareable object library file ("libfoo.so" in Unix
665                  terms) from the corresponding static library file
666                  or object files.
667
668                  called like this:
669
670                        libobj2shlib(shlib => "PATH/TO/shlibfile",
671                                     lib => "PATH/TO/libfile",
672                                     objs => [ "PATH/TO/objectfile", ... ],
673                                     deps => [ "PATH/TO/otherlibfile", ... ]);
674
675                  'lib' has the intended library file name *without*
676                  extension, libobj2shlib is expected to add that.
677                  'shlib' has the corresponding shared library name
678                  *without* extension.  'deps' has the list of other
679                  libraries (also *without* extension) this library
680                  needs to be linked with.  'objs' has the list of
681                  object files (also *without* extension) to build
682                  this library.
683
684                  This function has a choice; it can use the
685                  corresponding static library as input to make the
686                  shared library, or the list of object files.
687
688    obj2dso     - function that produces build file lines to build a
689                  dynamic shared object file from object files.
690
691                  called like this:
692
693                        obj2dso(lib => "PATH/TO/libfile",
694                                objs => [ "PATH/TO/objectfile", ... ],
695                                deps => [ "PATH/TO/otherlibfile",
696                                ... ]);
697
698                  This is almost the same as libobj2shlib, but the
699                  intent is to build a shareable library that can be
700                  loaded in runtime (a "plugin"...).  The differences
701                  are subtle, one of the most visible ones is that the
702                  resulting shareable library is produced from object
703                  files only.
704
705    obj2bin     - function that produces build file lines to build an
706                  executable file from object files.
707
708                  called like this:
709
710                        obj2bin(bin => "PATH/TO/binfile",
711                                objs => [ "PATH/TO/objectfile", ... ],
712                                deps => [ "PATH/TO/libfile", ... ]);
713
714                  'bin' has the intended executable file name
715                  *without* extension, obj2bin is expected to add
716                  that.  'objs' has the list of object files (also
717                  *without* extension) to build this library.  'deps'
718                  has the list of library files (also *without*
719                  extension) that the programs needs to be linked
720                  with.
721
722    in2script   - function that produces build file lines to build a
723                  script file from some input.
724
725                  called like this:
726
727                        in2script(script => "PATH/TO/scriptfile",
728                                  sources => [ "PATH/TO/infile", ... ]);
729
730                  'script' has the intended script file name.
731                  'sources' has the list of source files to build the
732                  resulting script from.
733
734In all cases, file file paths are relative to the build tree top, and
735the build file actions run with the build tree top as current working
736directory.
737
738Make sure to end the section with these functions with a string that
739you thing is appropriate for the resulting build file.  If nothing
740else, end it like this:
741
742      "";       # Make sure no lingering values end up in the Makefile
743    -}
744
745
746Configure helper scripts
747========================
748
749Configure uses helper scripts in this directory:
750
751Checker scripts
752---------------
753
754These scripts are per platform family, to check the integrity of the
755tools used for configuration and building.  The checker script used is
756either {build_platform}-{build_file}-checker.pm or
757{build_platform}-checker.pm, where {build_platform} is the second
758'build_scheme' list element from the configuration target data, and
759{build_file} is 'build_file' from the same target data.
760
761If the check succeeds, the script is expected to end with a non-zero
762expression.  If the check fails, the script can end with a zero, or
763with a `die`.
764