MAKEPP_EXTENDING(1) Makepp MAKEPP_EXTENDING(1)NAMEmakepp_extending-- How to extend makepp using Perl
DESCRIPTION
Makepp internally is flexible enough so that by writing a little bit of
Perl code, you can add functions or do a number of other operations.
General notes on writing Perl code to work with makepp
Each makefile lives in its own package. Thus definitions in one
makefile do not affect definitions in another makefile. A common set
of functions including all the standard textual manipulation functions
is imported into the package when it is created.
Makefile variables are stored as Perl scalars in that package. (There
are exceptions to this: automatic variables and the default value of
variables like CC are actually implemented as functions with no
arguments. Target specific vars, command line vars and environment
vars are not seen this way.) Thus any Perl code you write has access
to all makefile variables. Global variables are stored in the
"Mpp::global" package. See Makefile variables for the details.
Each of the statements (ifperl / ifmakeperl, perl / makeperl, sub /
makesub), the functions (perl / makeperl, map / makemap) and the rule
action (perl / makeperl) for writing Perl code directly in the makefile
come in two flavours. The first is absolutely normal Perl, meaning you
have to use the "f_" prefix as explained in the next section, if you
want to call makepp functions. The second variant first passes the
statement through Make-style variable expansion, meaning you have to
double the "$"s you want Perl to see.
End handling is special because makepp's huge (depending on your build
system) data structures would take several seconds to garbage collect
with a normal exit. So we do a brute force exit. In the main process
you can still have "END" blocks but if you have any global file handles
they may not get flushed. But you should be using the modern lexical
filehandles, which get closed properly when going out of scope.
In Perl code run directly as a rule action or via a command you define,
it is the opposite. "END" blocks will not be run, but global
filehandles get flushed for you. The "DESTROY" of global objects will
never be run.
Adding new textual functions
You can add a new function to makepp's repertoire by simply defining a
Perl subroutine of the same name but with a prefix of "f_". For
example:
sub f_myfunc {
my $argument = &arg; # Name the argument.
my( undef, $mkfile, $mkfile_line ) = @_; # Name the arguments.
... do something here
return $return_value;
}
XYZ := $(myfunc my func arguments)
If your function takes no arguments, there is nothing to do. If your
function takes one argument, as in the example above, use the simple
accessor &arg to obtain it. If you expect more arguments, you need the
more complex accessor "args" described below.
These accessors processes the same three parameters that should be
passed to any "f_" function, namely the function arguments, the
makefile object and a line descriptor for messages. Therefore you can
use the efficient &arg form in the first case.
The &arg accessor takes care of the following for you: If the arguments
were already expanded (e.g. to find the name of the function in
"$(my$(function) arg)" the arg is passed as a string and just returned.
If the argument still needs expansion, this is the usual case, it is
instead a reference to a string. The &arg accessor expands it for you,
for which it needs the makefile object as its 2nd parameter.
If you expect more arguments, possibly in variable number, the job is
performed by "args". This accessor takes the same 3 parameters as arg,
plus additional parameters:
max: number of args (default 2): give ~0 (maxint) for endless
min: number of args (default 0 if max is ~0, else same as max)
only_comma: don't eat space around commas, usual for non-filename
At most max, but at least min commas present before expansion are used
to split the arguments. Some examples from makepp's builtin functions:
my( $prefix, $text ) = args $_[0], $_[1], $_[2], 2, 2, 1; # addprefix
for my $cond ( args $_[0], undef, $_[2], ~0 ) ... # and, or
my @args= args $_[0], $_[1], $_[2], ~0, 1, 1; # call
my( $filters, $words ) = args $_[0], $_[1], $_[2]; # filter
The function should return a scalar string (not an array) which is then
inserted into the text at that point.
If your function encounters an error, it should die using the usual
Perl die statement. This will be trapped by makepp and an error
message displaying the file name and the line number of the expression
causing the error will be printed out.
There are essentially no limits on what the function can do; you can
access the file, run shell commands, etc.
At present, expressions appearing in dependencies and in the rule
actions are expanded once while expressions appearing in targets are
expanded twice, so be careful if your function has side effects and is
present in an expression for a target.
Note that the environment (in particular, the cwd) in which the
function evaluates will not necessarily match the environment in which
the rules from the Makefile in which the function was evaluated are
executed. If this is a problem for you, then your function probably
ought to look something like this:
sub f_foo {
...
chdir $makefile->{CWD};
... etc.
}
Putting functions into a Perl module
If you put functions into an include file, you will have one copy per
Makeppfile which uses it. To avoid that, you can write them as a
normal Perl module with an "Exporter" interface, and use that. This
will load faster and save memory:
perl { use mymodule }
perl {
use my::module; # put : on a new line so this is not parsed as a rule
}
If you need any of the functions normally available in a Makefile (like
the "f_" functions, "arg" or "args"), you must put this line into your
module:
use Mpp::Subs;
The drawback is that the module would be in a different package than a
function directly appearing in a makefile. So you need to pass in
everything as parameters, or construct names with Perl's "caller"
function.
Calling external Perl scripts
If you call an external Perl script via "system", or as a rule action,
makepp will fork a new process (unless it's the last rule action) and
fire off a brand new perl interpreter. There's nothing wrong with
that, except that there's a more efficient way:
&command arguments...
This can be a rule action. It will call a function command with a
"c_" prefix, and pass it the remaining (optionally quoted makepp
style -- not exactly the same as Shell) arguments. If such a
function cannot be found, this passes all strings to "run".
sub c_mycmd { my @args = @_; ... }
$(phony callcmd):
&mycmd 'arg with space' arg2 "arg3" # calls c_mycmd
%.out: %.in
&myscript -o $(output) $(input) # calls external myscript
You can write your commands within the framework of the builtins,
allowing you to use the same standard options as they have, and the
I/O handling they give.
The block operator "Mpp::Cmds::frame" is followed by a single
letter option list of the builtins (maximally "qw(f i I o O r s)").
Even if you specify your own option overriding one of these, you
still give the single letter of the standard option. Note how we
take one of the letter out of "qw()", because otherwise Perl 5.6
chokes.
Each own option is specified as "[qw(n name), \$ref, arg, sub]".
The first two elements are short and long name, followed by the
variable reference and optionally by a boolean for whether to take
an argument. Without an arg, the variable is incremented each time
the option is given, else the option value is stored in it.
sub c_my_ocmd { # Typical output case
local @ARGV = @_;
Mpp::Cmds::frame {
... print something here with @ARGV, with options already automatically removed
} 'f', qw(o O);
}
sub c_my_icmd { # Typical input case with 2 options
local @ARGV = @_;
my( $short, $long );
Mpp::Cmds::frame {
... do something here with <>
} qw(i I r s), # s specifies only --separator, not -s
[qw(s short), \$short], # No option arg -> $short == 1
[qw(l long), \$long, 1, sub { warn "got arg $long"}];
}
Here comes a simple command which upcases only the first character
of each input record (equivalent to "&sed '$$_ = "\u\L$$_"'"):
sub c_uc {
local @ARGV = @_;
Mpp::Cmds::frame {
print "\u\L$_" while <>;
} 'f', qw(i I o O r s);
}
Within the block handled by frame, you can have nested blocks for
performing critical operations, like opening other files.
Mpp::Cmds::perform { ... } 'message';
This will output message with "--verbose" (which every command
accepts) iff the command is successfully run. But if the block
evaluates as false, it dies with negated message.
run script arguments...
This is a normal Perl function you can use in any Perl context
within your makefile. It is similar to the multi-argument form of
system, but it runs the Perl script within the current process.
For makepp statements, the perl function or your own functions that
is the process running makepp. But for a rule that is the
subprocess performing it. The script gets parsed as many times as
it gets called, but you can put the real work into a lib, as
pod2html does. This lib can then get used in the top level, so
that it's already present:
perl { use mylib } # gets forked to all rules which needn't reparse it
%.out: %.in
makeperl { run qw'myscript -o $(output) $(input)' }
If the script calls "exit", closes standard file descriptors or
relies on the system to clean up after it (open files, memory...),
this can be a problem with "run". If you call "run" within
statements or the perl function, makepp can get disturbed or the
cleanup only happens at the end of makepp.
If you have one the aforementioned problems, run the script
externally, i.e. as from the command line instead. Within a rule
cleanup is less of a problem, especially not as the last action of
a rule, since the rule subprocess will exit afterwards anyway,
except on Windows.
Writing your own signature methods
Sometimes you want makepp to compute a signature method using a
different technique. For example, suppose you have a binary that
depends on a shared library. Ordinarily, if you change the shared
library, you don't have to relink executables that depend on it because
the linking is done at run time. (However, it is possible that
relinking the executable might be necessary, which is why I did not
make this the default.) What you want makepp to do is to have the same
signature for the shared library even if it changes.
This can be accomplished in several ways. The easiest way is to create
your own new signature method (let's call it "shared_object"). You
would use this signature method only on rules that link binaries, like
this:
myprogram : *.o lib1/lib1.so lib2/lib2.so
: signature shared_object
$(CC) $(inputs) -o $(output)
Now we have to create the signature method.
All signature methods must be their own class, and the class must
contain a few special items (see Mpp/Signature.pm in the distribution
for details). The class's name must be prefixed with
"Mpp::Signature::", so in this case our class should be called
"Mpp::Signature::shared_object". We have to create a file called
shared_object.pm and put it into a Mpp::Signature directory somewhere
in the Perl include path; the easiest place might be in the
Mpp/Signature directory in the makepp installation (e.g.,
/usr/local/share/makepp/Mpp/Signature or wherever you installed it).
For precise details about what has to go in this class, you should look
carefully through the file Mpp/Signature.pm and probably also
Mpp/Signature/exact_match.pm in the makepp distribution. But in our
case, all we want to do is to make a very small change to an existing
signature mechanism; if the file is a shared library, we want to have a
constant signature, whereas if the file is anything else, we want to
rely on makepp's normal signature mechanism. The best way to do this
is to inherit from "Mpp::Signature::c_compilation_md5", which is the
signature method that is usually chosen when makepp recognizes a link
command.
So the file Mpp/Signature/shared_object.pm might contain the following:
use strict;
package Mpp::Signature::shared_object;
use Mpp::Signature::c_compilation_md5;
our @ISA = qw(Mpp::Signature::c_compilation_md5); # Indicate inheritance.
our $shared_object = bless \@ISA; # A piece of magic that helps makepp find
# the subroutines for this method. All
# signature methods must have one of these.
# The value is not used, just any object.
# Now here's the method that gets called when we need the signature of
# any target or dependency for which this signature method is active:
sub signature {
my ($self, # This will be the same as $shared_object.
$finfo) = @_; # A special structure that contains everything
# makepp knows about this file. See
# Mpp/File.pm for details.
if ($finfo->{NAME} =~ /\.s[oa]$/) { # Does the file name end in .so or .sa?
return $finfo->file_exists ? 'exists' : '';
# Always return the same signature if the file
# exists. In this case, the signature is the
# string "exists".
}
Mpp::Signature::c_compilation_md5::signature;
# If the file didn't end in .so or .sa,
# delegate to makepp's usual signature method.
}
This file is provided as an example in the makepp distribution, with
some additional comments.
Incidentally, why don't we make this the default? Well, there are
times when changing a shared library will require a relinking of your
program. If you ever change either the symbols that a shared library
defines, or the symbols that it depends on other libraries for, a
relink may sometimes be necessary.
Suppose, for example, that the shared library invokes some subroutines
that your program provides. E.g., suppose you change the shared
library so it now calls an external subroutine "xyz()". Unless you use
the "-E" or "--export-dynamic" option to the linker (for GNU binutils;
other linkers have different option names), the symbol "xyz()" may not
be accessible to the run-time linker even if it exists in your program.
Even worse, suppose you defined "xyz()" in another library (call it
libxyz), like this:
my_program: main.o lib1/lib1.so xyz/libxyz.a
Since "libxyz" is a .a file and not a .so file, then "xyz()" may not be
pulled in correctly from libxyz.a unless you relink your binary.
Mpp::Signature methods also control not only the string that is used to
determine if a file has changed, but the algorithm that is used to
compare the strings. For example, the signature method "target_newer"
in the makepp distribution merely requires that the targets be newer
than the dependencies, whereas the signature method "exact_match" (and
everything that depends on it, such as "md5" and "c_compilation_md5")
requires that the file have the same signature as on the last build.
Here are some other kinds of signature methods that might be useful, to
help you realize the possibilities. If general purpose enough, some of
these may eventually be incorporated into makepp:
· A signature method for shared libraries that returns a checksum of
all the exported symbols, and also all the symbols that it needs
from other libraries. This solves the problem with the example
above, and guarantees a correct link under all circumstances. An
experimental attempt has been made to do this in the makepp
distribution (see Mpp/Signature/shared_object.pm), but it will only
work with GNU binutils and ELF libraries at the moment.
· A signature method that ignores a date stamp written into a file.
E.g., if you generate a .c file automatically using some program
that insists on putting a string in like this:
static char * date_stamp = "Generated automatically on 01 Apr 2004 by nobody";
you could write a signature method that specifically ignores
changes in date stamps. Thus if the date stamp is the only thing
that has changed, makepp will not rebuild.
· A signature method that computes the signatures the normal way, but
ignores the architecture dependence when deciding whether to
rebuild. This could be useful for truly architecture-independent
files; currently if you build on one architecture, makepp will
insist on rebuilding even architecture-independent files when you
switch to a different architecture.
· A signature method that knows how to ignore comments in latex
files, as the "c_compilation_md5" method knows how to ignore
comments in C files.
· A signature method for automatic documentation extraction that
checksums only to the comments that a documentation extractor needs
and ignores other changes to the source file.
Unfinished
This document is not finished yet. It should cover how to write your
own scanners for include files and things like that.
POD ERRORS
Hey! The above document had some coding errors, which are explained
below:
Around line 27:
alternative text 'ifperl / ifmakeperl' contains non-escaped | or /
alternative text 'perl / makeperl' contains non-escaped | or /
alternative text 'sub / makesub' contains non-escaped | or /
alternative text 'perl / makeperl' contains non-escaped | or /
alternative text 'map / makemap' contains non-escaped | or /
alternative text 'perl / makeperl' contains non-escaped | or /
perl v5.20.3 2012-02-07 MAKEPP_EXTENDING(1)
