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perlcompile ()
  • >> perlcompile (1) ( Solaris man: Команды и прикладные программы пользовательского уровня )
  • perlcompile (1) ( Разные man: Команды и прикладные программы пользовательского уровня )
  • 
    
    

    NAME

         perlcompile - Introduction to the Perl Compiler-Translator
    
    
    

    DESCRIPTION

         Perl has always had a compiler: your source is compiled into
         an internal form (a parse tree) which is then optimized
         before being run.  Since version 5.005, Perl has shipped
         with a module capable of inspecting the optimized parse tree
         (`B'), and this has been used to write many useful
         utilities, including a module that lets you turn your Perl
         into C source code that can be compiled into an native
         executable.
    
         The `B' module provides access to the parse tree, and other
         modules ("back ends") do things with the tree.  Some write
         it out as bytecode, C source code, or a semi-human-readable
         text.  Another traverses the parse tree to build a cross-
         reference of which subroutines, formats, and variables are
         used where.  Another checks your code for dubious
         constructs.  Yet another back end dumps the parse tree back
         out as Perl source, acting as a source code beautifier or
         deobfuscator.
    
         Because its original purpose was to be a way to produce C
         code corresponding to a Perl program, and in turn a native
         executable, the `B' module and its associated back ends are
         known as "the compiler", even though they don't really
         compile anything.  Different parts of the compiler are more
         accurately a "translator", or an "inspector", but people
         want Perl to have a "compiler option" not an "inspector
         gadget".  What can you do?
    
         This document covers the use of the Perl compiler: which
         modules it comprises, how to use the most important of the
         back end modules, what problems there are, and how to work
         around them.
    
         Layout
    
         The compiler back ends are in the `B::' hierarchy, and the
         front-end (the module that you, the user of the compiler,
         will sometimes interact with) is the O module.  Some back
         ends (e.g., `B::C') have programs (e.g., perlcc) to hide the
         modules' complexity.
    
         Here are the important back ends to know about, with their
         status expressed as a number from 0 (outline for later
         implementation) to 10 (if there's a bug in it, we're very
         surprised):
    
         B::Bytecode
             Stores the parse tree in a machine-independent format,
             suitable for later reloading through the ByteLoader
             module.  Status: 5 (some things work, some things don't,
             some things are untested).
    
         B::C
             Creates a C source file containing code to rebuild the
             parse tree and resume the interpreter.  Status: 6 (many
             things work adequately, including programs using Tk).
    
         B::CC
             Creates a C source file corresponding to the run time
             code path in the parse tree.  This is the closest to a
             Perl-to-C translator there is, but the code it generates
             is almost incomprehensible because it translates the
             parse tree into a giant switch structure that
             manipulates Perl structures.  Eventual goal is to reduce
             (given sufficient type information in the Perl program)
             some of the Perl data structure manipulations into
             manipulations of C-level ints, floats, etc.  Status: 5
             (some things work, including uncomplicated Tk examples).
    
         B::Lint
             Complains if it finds dubious constructs in your source
             code.  Status:  6 (it works adequately, but only has a
             very limited number of areas that it checks).
    
         B::Deparse
             Recreates the Perl source, making an attempt to format
             it coherently.  Status: 8 (it works nicely, but a few
             obscure things are missing).
    
         B::Xref
             Reports on the declaration and use of subroutines and
             variables.  Status: 8 (it works nicely, but still has a
             few lingering bugs).
    
    
    

    Using The Back Ends

         The following sections describe how to use the various
         compiler back ends.  They're presented roughly in order of
         maturity, so that the most stable and proven back ends are
         described first, and the most experimental and incomplete
         back ends are described last.
    
         The O module automatically enabled the -c flag to Perl,
         which prevents Perl from executing your code once it has
         been compiled.  This is why all the back ends print:
    
           myperlprogram syntax OK
    
         before producing any other output.
    
    
         The Cross Referencing Back End
    
         The cross referencing back end (B::Xref) produces a report
         on your program, breaking down declarations and uses of
         subroutines and variables (and formats) by file and
         subroutine.  For instance, here's part of the report from
         the pod2man program that comes with Perl:
    
           Subroutine clear_noremap
             Package (lexical)
               $ready_to_print   i1069, 1079
             Package main
               $&                1086
               $.                1086
               $0                1086
               $1                1087
               $2                1085, 1085
               $3                1085, 1085
               $ARGV             1086
               %HTML_Escapes     1085, 1085
    
         This shows the variables used in the subroutine
         `clear_noremap'.  The variable `$ready_to_print' is a my()
         (lexical) variable, introduced (first declared with my()) on
         line 1069, and used on line 1079.  The variable `$&' from
         the main package is used on 1086, and so on.
    
         A line number may be prefixed by a single letter:
    
         i   Lexical variable introduced (declared with my()) for the
             first time.
    
         &   Subroutine or method call.
    
         s   Subroutine defined.
    
         r   Format defined.
    
         The most useful option the cross referencer has is to save
         the report to a separate file.  For instance, to save the
         report on myperlprogram to the file report:
    
           $ perl -MO=Xref,-oreport myperlprogram
    
    
         The Decompiling Back End
    
         The Deparse back end turns your Perl source back into Perl
         source.  It can reformat along the way, making it useful as
         a de-obfuscator.  The most basic way to use it is:
    
    
           $ perl -MO=Deparse myperlprogram
    
         You'll notice immediately that Perl has no idea of how to
         paragraph your code.  You'll have to separate chunks of code
         from each other with newlines by hand.  However, watch what
         it will do with one-liners:
    
           $ perl -MO=Deparse -e '$op=shift||die "usage: $0
           code [...]";chomp(@ARGV=<>)unless@ARGV; for(@ARGV){$was=$_;eval$op;
           die$@ if$@; rename$was,$_ unless$was eq $_}'
           -e syntax OK
           $op = shift @ARGV || die("usage: $0 code [...]");
           chomp(@ARGV = <ARGV>) unless @ARGV;
           foreach $_ (@ARGV) {
               $was = $_;
               eval $op;
               die $@ if $@;
               rename $was, $_ unless $was eq $_;
           }
    
         (this is the rename program that comes in the eg/ directory
         of the Perl source distribution).
    
         The decompiler has several options for the code it
         generates.  For instance, you can set the size of each
         indent from 4 (as above) to 2 with:
    
           $ perl -MO=Deparse,-si2 myperlprogram
    
         The -p option adds parentheses where normally they are
         omitted:
    
           $ perl -MO=Deparse -e 'print "Hello, world\n"'
           -e syntax OK
           print "Hello, world\n";
           $ perl -MO=Deparse,-p -e 'print "Hello, world\n"'
           -e syntax OK
           print("Hello, world\n");
    
         See the B::Deparse manpage for more information on the
         formatting options.
    
         The Lint Back End
    
         The lint back end (B::Lint) inspects programs for poor
         style.  One programmer's bad style is another programmer's
         useful tool, so options let you select what is complained
         about.
    
         To run the style checker across your source code:
    
    
           $ perl -MO=Lint myperlprogram
    
         To disable context checks and undefined subroutines:
    
           $ perl -MO=Lint,-context,-undefined-subs myperlprogram
    
         See the B::Lint manpage for information on the options.
    
         The Simple C Back End
    
         This module saves the internal compiled state of your Perl
         program to a C source file, which can be turned into a
         native executable for that particular platform using a C
         compiler.  The resulting program links against the Perl
         interpreter library, so it will not save you disk space
         (unless you build Perl with a shared library) or program
         size.  It may, however, save you startup time.
    
         The `perlcc' tool generates such executables by default.
    
           perlcc myperlprogram.pl
    
    
         The Bytecode Back End
    
         This back end is only useful if you also have a way to load
         and execute the bytecode that it produces.  The ByteLoader
         module provides this functionality.
    
         To turn a Perl program into executable byte code, you can
         use `perlcc' with the `-b' switch:
    
           perlcc -b myperlprogram.pl
    
         The byte code is machine independent, so once you have a
         compiled module or program, it is as portable as Perl source
         (assuming that the user of the module or program has a
         modern-enough Perl interpreter to decode the byte code).
    
         See B::Bytecode for information on options to control the
         optimization and nature of the code generated by the
         Bytecode module.
    
         The Optimized C Back End
    
         The optimized C back end will turn your Perl program's run
         time code-path into an equivalent (but optimized) C program
         that manipulates the Perl data structures directly.  The
         program will still link against the Perl interpreter
         library, to allow for eval(), `s///e', `require', etc.
    
    
         The `perlcc' tool generates such executables when using the
         -opt switch.  To compile a Perl program (ending in `.pl' or
         `.p'):
    
           perlcc -opt myperlprogram.pl
    
         To produce a shared library from a Perl module (ending in
         `.pm'):
    
           perlcc -opt Myperlmodule.pm
    
         For more information, see the perlcc manpage and the B::CC
         manpage.
    
         B   This module is the introspective ("reflective" in Java
             terms) module, which allows a Perl program to inspect
             its innards.  The back end modules all use this module
             to gain access to the compiled parse tree.  You, the
             user of a back end module, will not need to interact
             with B.
    
         O   This module is the front-end to the compiler's back
             ends.  Normally called something like this:
    
               $ perl -MO=Deparse myperlprogram
    
             This is like saying `use O 'Deparse'' in your Perl
             program.
    
         B::Asmdata
             This module is used by the B::Assembler module, which is
             in turn used by the B::Bytecode module, which stores a
             parse-tree as bytecode for later loading.  It's not a
             back end itself, but rather a component of a back end.
    
         B::Assembler
             This module turns a parse-tree into data suitable for
             storing and later decoding back into a parse-tree.  It's
             not a back end itself, but rather a component of a back
             end.  It's used by the assemble program that produces
             bytecode.
    
         B::Bblock
             This module is used by the B::CC back end.  It walks
             "basic blocks".  A basic block is a series of operations
             which is known to execute from start to finish, with no
             possiblity of branching or halting.
    
         B::Bytecode
             This module is a back end that generates bytecode from a
             program's parse tree.  This bytecode is written to a
             file, from where it can later be reconstructed back into
             a parse tree.  The goal is to do the expensive program
             compilation once, save the interpreter's state into a
             file, and then restore the state from the file when the
             program is to be executed.  See the The Bytecode Back
             End entry elsewhere in this document for details about
             usage.
    
         B::C
             This module writes out C code corresponding to the parse
             tree and other interpreter internal structures.  You
             compile the corresponding C file, and get an executable
             file that will restore the internal structures and the
             Perl interpreter will begin running the program.  See
             the The Simple C Back End entry elsewhere in this
             document for details about usage.
    
         B::CC
             This module writes out C code corresponding to your
             program's operations.  Unlike the B::C module, which
             merely stores the interpreter and its state in a C
             program, the B::CC module makes a C program that does
             not involve the interpreter.  As a consequence, programs
             translated into C by B::CC can execute faster than
             normal interpreted programs.  See the The Optimized C
             Back End entry elsewhere in this document for details
             about usage.
    
         B::Debug
             This module dumps the Perl parse tree in verbose detail
             to STDOUT.  It's useful for people who are writing their
             own back end, or who are learning about the Perl
             internals.  It's not useful to the average programmer.
    
         B::Deparse
             This module produces Perl source code from the compiled
             parse tree.  It is useful in debugging and
             deconstructing other people's code, also as a pretty-
             printer for your own source.  See the The Decompiling
             Back End entry elsewhere in this document for details
             about usage.
    
         B::Disassembler
             This module turns bytecode back into a parse tree.  It's
             not a back end itself, but rather a component of a back
             end.  It's used by the disassemble program that comes
             with the bytecode.
    
         B::Lint
             This module inspects the compiled form of your source
             code for things which, while some people frown on them,
             aren't necessarily bad enough to justify a warning.  For
             instance, use of an array in scalar context without
             explicitly saying `scalar(@array)' is something that
             Lint can identify.  See the The Lint Back End entry
             elsewhere in this document for details about usage.
    
         B::Showlex
             This module prints out the my() variables used in a
             function or a file.  To gt a list of the my() variables
             used in the subroutine mysub() defined in the file
             myperlprogram:
    
               $ perl -MO=Showlex,mysub myperlprogram
    
             To gt a list of the my() variables used in the file
             myperlprogram:
    
               $ perl -MO=Showlex myperlprogram
    
             [BROKEN]
    
         B::Stackobj
             This module is used by the B::CC module.  It's not a
             back end itself, but rather a component of a back end.
    
         B::Stash
             This module is used by the the perlcc manpage program,
             which compiles a module into an executable.  B::Stash
             prints the symbol tables in use by a program, and is
             used to prevent B::CC from producing C code for the B::*
             and O modules.  It's not a back end itself, but rather a
             component of a back end.
    
         B::Terse
             This module prints the contents of the parse tree, but
             without as much information as B::Debug.  For
             comparison, `print "Hello, world."'  produced 96 lines
             of output from B::Debug, but only 6 from B::Terse.
    
             This module is useful for people who are writing their
             own back end, or who are learning about the Perl
             internals.  It's not useful to the average programmer.
    
         B::Xref
             This module prints a report on where the variables,
             subroutines, and formats are defined and used within a
             program and the modules it loads.  See the The Cross
             Referencing Back End entry elsewhere in this document
             for details about usage.
    
    
    

    KNOWN PROBLEMS

         The simple C backend currently only saves typeglobs with
         alphanumeric names.
    
         The optimized C backend outputs code for more modules than
         it should (e.g., DirHandle).  It also has little hope of
         properly handling `goto LABEL' outside the running
         subroutine (`goto &sub' is ok).  `goto LABEL' currently does
         not work at all in this backend.  It also creates a huge
         initialization function that gives C compilers headaches.
         Splitting the initialization function gives better results.
         Other problems include: unsigned math does not work
         correctly; some opcodes are handled incorrectly by default
         opcode handling mechanism.
    
         BEGIN{} blocks are executed while compiling your code.  Any
         external state that is initialized in BEGIN{}, such as
         opening files, initiating database connections etc., do not
         behave properly.  To work around this, Perl has an INIT{}
         block that corresponds to code being executed before your
         program begins running but after your program has finished
         being compiled.  Execution order: BEGIN{}, (possible save of
         state through compiler back-end), INIT{}, program runs,
         END{}.
    
    
    

    AUTHOR

         This document was originally written by Nathan Torkington,
         and is now maintained by the perl5-porters mailing list
         perl5-porters@perl.org.
    
    
    
    


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