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CRUNCHGEN(1) General Commands Manual CRUNCHGEN(1)

crunchgen — generates build environment for a crunched binary

crunchgen [-foql] [-h makefile-header-name] [-m makefile-name] [-p obj-prefix] [-c c-file-name] [-e exec-file-name] conf-file

A crunched binary is a program made up of many other programs linked together into a single executable. The crunched binary () function determines which component program to run by the contents of argv[0]. The main reason to crunch programs together is for fitting as many programs as possible onto an installation or system recovery floppy.

The crunchgen utility reads in the specifications in conf-file for a crunched binary, and generates a Makefile and accompanying top-level C source file that when built creates the crunched executable file from the component programs. For each component program, crunchgen can optionally attempt to determine the object (.o) files that make up the program from its source directory Makefile. This information is cached between runs. The crunchgen utility uses the companion program crunchide(1) to eliminate link-time conflicts between the component programs by hiding all unnecessary symbols.

The crunchgen utility places specific requirements on package Makefiles which make it unsuitable for use with non-BSD sources. In particular, the Makefile must contain the target depend, and it must define all object files in the variable OBJS. In some cases, you can use a fake Makefile: before looking for Makefile in the source directory foo, crunchgen looks for the file Makefile.foo in the current directory.

After crunchgen is run, the crunched binary can be built by running “make -f <conf-name>.mk”. The component programs' object files must already be built. An objs target, included in the output makefile, will run make(1) in each component program's source dir to build the object files for the user. This is not done automatically since in release engineering circumstances it is generally not desirable to be modifying objects in other directories.

The options are as follows:

c-file-name
Set output C file name to c-file-name. The default name is <conf-name>.c.
exec-file-name
Set crunched binary executable file name to exec-file-name. The default name is <conf-name>.
Flush cache. Forces the recalculation of cached parameters.
List names. Lists the names this binary will respond to.
makefile-header-name
Set the name of a file to be included at the beginning of the Makefiles generated by crunchgen. This is useful to define some make variables such as RELEASE_CRUNCH or similar, which might affect the behavior of make(1) and are annoying to pass through environment variables.
makefile-name
Set output Makefile name to makefile-name. The default name is <conf-name>.mk.
Add “make obj” rules to each program make target.
obj-prefix
Set the pathname to be prepended to the srcdir when computing the objdir. If this option is not present, then the prefix used is the content of the MAKEOBJDIRPREFIX environment variable, or /usr/obj.
Quiet operation. Status messages are suppressed.

The crunchgen utility reads specifications from the conf-file that describe the components of the crunched binary. In its simplest use, the component program names are merely listed along with the top-level source directories in which their sources can be found. The crunchgen utility then calculates (via the source makefiles) and caches the list of object files and their locations. For more specialized situations, the user can specify by hand all the parameters that crunchgen needs.

The conf-file commands are as follows:

dirname ...
A list of source trees in which the source directories of the component programs can be found. These dirs are searched using the BSD “<source-dir>/<progname>/” convention. Multiple srcdirs lines can be specified. The directories are searched in the order they are given.
progname ...
A list of programs that make up the crunched binary. Multiple progs lines can be specified.
libspec ...
A list of library specifications to be included in the crunched binary link. Multiple libs lines can be specified.
libspec ...
A list of library specifications to be dynamically linked in the crunched binary. These libraries will need to be made available via the run-time link-editor rtld(1) when the component program that requires them is executed from the crunched binary. Multiple libs_so lines can be specified. The libs_so directive overrides a library specified gratuitously on a libs line.
buildopts ...
A list of build options to be added to every make target.
progname linkname
Causes the crunched binary to invoke progname whenever linkname appears in argv[0]. This allows programs that change their behavior when run under different names to operate correctly.

To handle specialized situations, such as when the source is not available or not built via a conventional Makefile, the following special commands can be used to set crunchgen parameters for a component program.

progname srcdir pathname
Set the source directory for progname. This is normally calculated by searching the specified srcdirs for a directory named progname.
progname objdir pathname
Set the obj directory for progname. The obj directory is normally calculated by looking for a directory whose name is that of the source directory prepended by one of the following components, in order of priority: the -p argument passed to the command line; or, the value of the MAKEOBJDIRPREFIX environment variable, or /usr/obj. If the directory is not found, the srcdir itself becomes the objdir.
progname buildopts buildopts
Define a set of build options that should be added to make(1) targets in addition to those specified using buildopts when processing progname.
progname objs object-file-name ...
Set the list of object files for program progname. This is normally calculated by constructing a temporary makefile that includes “srcdir/Makefile” and outputs the value of $(OBJS).
progname objpaths full-pathname-to-object-file ...
Sets the pathnames of the object files for program progname. This is normally calculated by prepending the objdir pathname to each file in the objs list.
progname objvar variable_name
Sets the name of the make(1) variable which holds the list of object files for program progname. This is normally OBJS but some Makefiles might like to use other conventions or prepend the program's name to the variable, e.g., SSHD_OBJS.
progname lib library-name ...
Specifies libraries to be linked with object files to produce progname.lo. This can be useful with libraries which redefine routines in the standard libraries, or poorly written libraries which reference symbols in the object files.
progname keep symbol-name ...
Add specified list of symbols to the keep list for program progname. An underscore (‘_’) is prepended to each symbol and it becomes the argument to a -k option for the crunchide(1) phase. This option is to be used as a last resort as its use can cause a symbol conflict, however in certain instances it may be the only way to have a symbol resolve.
progname ident identifier
Set the Makefile/C identifier for progname. This is normally generated from a progname, mapping ‘-’ to ‘_’ and ignoring all other non-identifier characters. This leads to programs named "foo.bar" and "foobar" to map to the same identifier.

Only the objpaths parameter is actually needed by crunchgen, but it is calculated from objdir and objs, which are in turn calculated from srcdir, so is sometimes convenient to specify the earlier parameters and let crunchgen calculate forward from there if it can.

The makefile produced by crunchgen contains an optional objs target that will build the object files for each component program by running make(1) inside that program's source directory. For this to work the srcdir and objs parameters must also be valid. If they are not valid for a particular program, that program is skipped in the objs target.

Here is an example crunchgen input conf file, named “kcopy.conf”:

srcdirs /usr/src/bin /usr/src/sbin

progs test cp echo sh fsck halt init mount umount myinstall
progs anotherprog
ln test [       # test can be invoked via [
ln sh -sh       # init invokes the shell with "-sh" in argv[0]

special myprog objpaths /homes/leroy/src/myinstall.o # no sources

special anotherprog -DNO_FOO WITHOUT_BAR=YES

libs -lutil -lcrypt

This conf file specifies a small crunched binary consisting of some basic system utilities plus a homegrown install program “myinstall”, for which no source directory is specified, but its object file is specified directly with the special line.

Additionally when “anotherprog” is built the arguments

-DNO_FOO WITHOUT_BAR=YES

are added to all build targets.

The crunched binary “kcopy” can be built as follows:

% crunchgen -m Makefile kcopy.conf    # gen Makefile and kcopy.c
% make objs             # build the component programs' .o files
% make                  # build the crunched binary kcopy
% kcopy sh              # test that this invokes a sh shell
$			# it works!

At this point the binary “kcopy” can be copied onto an install floppy and hard-linked to the names of the component programs.

Note that if the libs_so command had been used, copies of the libraries so named would also need to be copied to the install floppy.

crunchide(1), make(1), rtld(1)

The crunchgen utility was written by James da Silva <jds@cs.umd.edu>.

Copyright (c) 1994 University of Maryland. All Rights Reserved.

The libs_so keyword was added in 2005 by Adrian Steinmann <ast@marabu.ch> and Ceri Davies <ceri@FreeBSD.org>.

While crunchgen takes care to eliminate link conflicts between the component programs of a crunched binary, conflicts are still possible between the libraries that are linked in. Some shuffling in the order of libraries may be required, and in some rare cases two libraries may have an unresolvable conflict and thus cannot be crunched together.

Some versions of the BSD build environment do not by default build the intermediate object file for single-source file programs. The “make objs” must then be used to get those object files built, or some other arrangements made.

January 6, 2017 FreeBSD-12.0