b.pm

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#      B.pm
#
#      Copyright (c) 1996, 1997, 1998 Malcolm Beattie
#
#      You may distribute under the terms of either the GNU General Public
#      License or the Artistic License, as specified in the README file.
#
package B;

our $VERSION = '1.17';

use XSLoader ();
require Exporter;
@ISA = qw(Exporter);

# walkoptree_slow comes from B.pm (you are there),
# walkoptree comes from B.xs
@EXPORT_OK = qw(minus_c ppname save_BEGINs
		class peekop cast_I32 cstring cchar hash threadsv_names
		main_root main_start main_cv svref_2object opnumber
		sub_generation amagic_generation perlstring
		walkoptree_slow walkoptree walkoptree_exec walksymtable
		parents comppadlist sv_undef compile_stats timing_info
		begin_av init_av check_av end_av regex_padav dowarn defstash
		curstash warnhook diehook inc_gv @optype @specialsv_name
		);
push @EXPORT_OK, qw(unitcheck_av) if $] > 5.009;

sub OPf_KIDS ();
use strict;
@B::SV::ISA = 'B::OBJECT';
@B::NULL::ISA = 'B::SV';
@B::PV::ISA = 'B::SV';
@B::IV::ISA = 'B::SV';
@B::NV::ISA = 'B::SV';
@B::RV::ISA = 'B::SV';
@B::PVIV::ISA = qw(B::PV B::IV);
@B::PVNV::ISA = qw(B::PVIV B::NV);
@B::PVMG::ISA = 'B::PVNV';
# Change in the inheritance hierarchy post 5.9.0
@B::PVLV::ISA = $] > 5.009 ? 'B::GV' : 'B::PVMG';
# BM is eliminated post 5.9.5, but effectively is a specialisation of GV now.
@B::BM::ISA = $] > 5.009005 ? 'B::GV' : 'B::PVMG';
@B::AV::ISA = 'B::PVMG';
@B::GV::ISA = 'B::PVMG';
@B::HV::ISA = 'B::PVMG';
@B::CV::ISA = 'B::PVMG';
@B::IO::ISA = 'B::PVMG';
@B::FM::ISA = 'B::CV';

@B::OP::ISA = 'B::OBJECT';
@B::UNOP::ISA = 'B::OP';
@B::BINOP::ISA = 'B::UNOP';
@B::LOGOP::ISA = 'B::UNOP';
@B::LISTOP::ISA = 'B::BINOP';
@B::SVOP::ISA = 'B::OP';
@B::PADOP::ISA = 'B::OP';
@B::PVOP::ISA = 'B::OP';
@B::LOOP::ISA = 'B::LISTOP';
@B::PMOP::ISA = 'B::LISTOP';
@B::COP::ISA = 'B::OP';

@B::SPECIAL::ISA = 'B::OBJECT';

@B::optype = qw(OP UNOP BINOP LOGOP LISTOP PMOP SVOP PADOP PVOP LOOP COP);
# bytecode.pl contained the following comment:
# Nullsv *must* come first in the following so that the condition
# ($$sv == 0) can continue to be used to test (sv == Nullsv).
@B::specialsv_name = qw(Nullsv &PL_sv_undef &PL_sv_yes &PL_sv_no
			(SV*)pWARN_ALL (SV*)pWARN_NONE (SV*)pWARN_STD);

{
    # Stop "-w" from complaining about the lack of a real B::OBJECT class
    package B::OBJECT;
}

sub B::GV::SAFENAME {
  my $name = (shift())->NAME;

  # The regex below corresponds to the isCONTROLVAR macro
  # from toke.c

  $name =~ s/^([\cA-\cZ\c\\c[\c]\c?\c_\c^])/"^".
	chr( utf8::unicode_to_native( 64 ^ ord($1) ))/e;

  # When we say unicode_to_native we really mean ascii_to_native,
  # which matters iff this is a non-ASCII platform (EBCDIC).

  return $name;
}

sub B::IV::int_value {
  my ($self) = @_;
  return (($self->FLAGS() & SVf_IVisUV()) ? $self->UVX : $self->IV);
}

sub B::NULL::as_string() {""}
sub B::IV::as_string()   {goto &B::IV::int_value}
sub B::PV::as_string()   {goto &B::PV::PV}

my $debug;
my $op_count = 0;
my @parents = ();

sub debug {
    my ($class, $value) = @_;
    $debug = $value;
    walkoptree_debug($value);
}

sub class {
    my $obj = shift;
    my $name = ref $obj;
    $name =~ s/^.*:://;
    return $name;
}

sub parents { \@parents }

# For debugging
sub peekop {
    my $op = shift;
    return sprintf("%s (0x%x) %s", class($op), $$op, $op->name);
}

sub walkoptree_slow {
    my($op, $method, $level) = @_;
    $op_count++; # just for statistics
    $level ||= 0;
    warn(sprintf("walkoptree: %d. %s\n", $level, peekop($op))) if $debug;
    $op->$method($level) if $op->can($method);
    if ($$op && ($op->flags & OPf_KIDS)) {
	my $kid;
	unshift(@parents, $op);
	for ($kid = $op->first; $$kid; $kid = $kid->sibling) {
	    walkoptree_slow($kid, $method, $level + 1);
	}
	shift @parents;
    }
    if (class($op) eq 'PMOP'
	&& ref($op->pmreplroot)
	&& ${$op->pmreplroot}
	&& $op->pmreplroot->isa( 'B::OP' ))
    {
	unshift(@parents, $op);
	walkoptree_slow($op->pmreplroot, $method, $level + 1);
	shift @parents;
    }
}

sub compile_stats {
    return "Total number of OPs processed: $op_count\n";
}

sub timing_info {
    my ($sec, $min, $hr) = localtime;
    my ($user, $sys) = times;
    sprintf("%02d:%02d:%02d user=$user sys=$sys",
	    $hr, $min, $sec, $user, $sys);
}

my %symtable;

sub clearsym {
    %symtable = ();
}

sub savesym {
    my ($obj, $value) = @_;
#    warn(sprintf("savesym: sym_%x => %s\n", $$obj, $value)); # debug
    $symtable{sprintf("sym_%x", $$obj)} = $value;
}

sub objsym {
    my $obj = shift;
    return $symtable{sprintf("sym_%x", $$obj)};
}

sub walkoptree_exec {
    my ($op, $method, $level) = @_;
    $level ||= 0;
    my ($sym, $ppname);
    my $prefix = "    " x $level;
    for (; $$op; $op = $op->next) {
	$sym = objsym($op);
	if (defined($sym)) {
	    print $prefix, "goto $sym\n";
	    return;
	}
	savesym($op, sprintf("%s (0x%lx)", class($op), $$op));
	$op->$method($level);
	$ppname = $op->name;
	if ($ppname =~
	    /^(d?or(assign)?|and(assign)?|mapwhile|grepwhile|entertry|range|cond_expr)$/)
	{
	    print $prefix, uc($1), " => {\n";
	    walkoptree_exec($op->other, $method, $level + 1);
	    print $prefix, "}\n";
	} elsif ($ppname eq "match" || $ppname eq "subst") {
	    my $pmreplstart = $op->pmreplstart;
	    if ($$pmreplstart) {
		print $prefix, "PMREPLSTART => {\n";
		walkoptree_exec($pmreplstart, $method, $level + 1);
		print $prefix, "}\n";
	    }
	} elsif ($ppname eq "substcont") {
	    print $prefix, "SUBSTCONT => {\n";
	    walkoptree_exec($op->other->pmreplstart, $method, $level + 1);
	    print $prefix, "}\n";
	    $op = $op->other;
	} elsif ($ppname eq "enterloop") {
	    print $prefix, "REDO => {\n";
	    walkoptree_exec($op->redoop, $method, $level + 1);
	    print $prefix, "}\n", $prefix, "NEXT => {\n";
	    walkoptree_exec($op->nextop, $method, $level + 1);
	    print $prefix, "}\n", $prefix, "LAST => {\n";
	    walkoptree_exec($op->lastop,  $method, $level + 1);
	    print $prefix, "}\n";
	} elsif ($ppname eq "subst") {
	    my $replstart = $op->pmreplstart;
	    if ($$replstart) {
		print $prefix, "SUBST => {\n";
		walkoptree_exec($replstart, $method, $level + 1);
		print $prefix, "}\n";
	    }
	}
    }
}

sub walksymtable {
    my ($symref, $method, $recurse, $prefix) = @_;
    my $sym;
    my $ref;
    my $fullname;
    no strict 'refs';
    $prefix = '' unless defined $prefix;
    while (($sym, $ref) = each %$symref) {
        $fullname = "*main::".$prefix.$sym;
	if ($sym =~ /::$/) {
	    $sym = $prefix . $sym;
	    if ($sym ne "main::" && $sym ne "<none>::" && &$recurse($sym)) {
               walksymtable(\%$fullname, $method, $recurse, $sym);
	    }
	} else {
           svref_2object(\*$fullname)->$method();
	}
    }
}

{
    package B::Section;
    my $output_fh;
    my %sections;

    sub new {
	my ($class, $section, $symtable, $default) = @_;
	$output_fh ||= FileHandle->new_tmpfile;
	my $obj = bless [-1, $section, $symtable, $default], $class;
	$sections{$section} = $obj;
	return $obj;
    }

    sub get {
	my ($class, $section) = @_;
	return $sections{$section};
    }

    sub add {
	my $section = shift;
	while (defined($_ = shift)) {
	    print $output_fh "$section->[1]\t$_\n";
	    $section->[0]++;
	}
    }

    sub index {
	my $section = shift;
	return $section->[0];
    }

    sub name {
	my $section = shift;
	return $section->[1];
    }

    sub symtable {
	my $section = shift;
	return $section->[2];
    }

    sub default {
	my $section = shift;
	return $section->[3];
    }

    sub output {
	my ($section, $fh, $format) = @_;
	my $name = $section->name;
	my $sym = $section->symtable || {};
	my $default = $section->default;

	seek($output_fh, 0, 0);
	while (<$output_fh>) {
	    chomp;
	    s/^(.*?)\t//;
	    if ($1 eq $name) {
		s{(s\\_[0-9a-f]+)} {
		    exists($sym->{$1}) ? $sym->{$1} : $default;
		}ge;
		printf $fh $format, $_;
	    }
	}
    }
}

XSLoader::load 'B';

1;

__END__

=head1 NAME

B - The Perl Compiler

=head1 SYNOPSIS

	use B;

=head1 DESCRIPTION

The C<B> module supplies classes which allow a Perl program to delve
into its own innards. It is the module used to implement the
"backends" of the Perl compiler. Usage of the compiler does not
require knowledge of this module: see the F<O> module for the
user-visible part. The C<B> module is of use to those who want to
write new compiler backends. This documentation assumes that the
reader knows a fair amount about perl's internals including such
things as SVs, OPs and the internal symbol table and syntax tree
of a program.

=head1 OVERVIEW

The C<B> module contains a set of utility functions for querying the
current state of the Perl interpreter; typically these functions
return objects from the B::SV and B::OP classes, or their derived
classes.  These classes in turn define methods for querying the
resulting objects about their own internal state.

=head1 Utility Functions

The C<B> module exports a variety of functions: some are simple
utility functions, others provide a Perl program with a way to
get an initial "handle" on an internal object.

=head2 Functions Returning C<B::SV>, C<B::AV>, C<B::HV>, and C<B::CV> objects

For descriptions of the class hierarchy of these objects and the
methods that can be called on them, see below, L<"OVERVIEW OF
CLASSES"> and L<"SV-RELATED CLASSES">.

=over 4

=item sv_undef

Returns the SV object corresponding to the C variable C<sv_undef>.

=item sv_yes

Returns the SV object corresponding to the C variable C<sv_yes>.

=item sv_no

Returns the SV object corresponding to the C variable C<sv_no>.

=item svref_2object(SVREF)

Takes a reference to any Perl value, and turns the referred-to value
into an object in the appropriate B::OP-derived or B::SV-derived
class. Apart from functions such as C<main_root>, this is the primary
way to get an initial "handle" on an internal perl data structure
which can then be followed with the other access methods.

The returned object will only be valid as long as the underlying OPs
and SVs continue to exist. Do not attempt to use the object after the
underlying structures are freed.

=item amagic_generation

Returns the SV object corresponding to the C variable C<amagic_generation>.

=item init_av

Returns the AV object (i.e. in class B::AV) representing INIT blocks.

=item check_av

Returns the AV object (i.e. in class B::AV) representing CHECK blocks.

=item unitcheck_av

Returns the AV object (i.e. in class B::AV) representing UNITCHECK blocks.

=item begin_av

Returns the AV object (i.e. in class B::AV) representing BEGIN blocks.

=item end_av

Returns the AV object (i.e. in class B::AV) representing END blocks.

=item comppadlist

Returns the AV object (i.e. in class B::AV) of the global comppadlist.

=item regex_padav

Only when perl was compiled with ithreads.

=item main_cv

Return the (faked) CV corresponding to the main part of the Perl
program.

=back

=head2 Functions for Examining the Symbol Table

=over 4

=item walksymtable(SYMREF, METHOD, RECURSE, PREFIX)

Walk the symbol table starting at SYMREF and call METHOD on each
symbol (a B::GV object) visited.  When the walk reaches package
symbols (such as "Foo::") it invokes RECURSE, passing in the symbol
name, and only recurses into the package if that sub returns true.

PREFIX is the name of the SYMREF you're walking.

For example:

  # Walk CGI's symbol table calling print_subs on each symbol.
  # Recurse only into CGI::Util::
  walksymtable(\%CGI::, 'print_subs', sub { $_[0] eq 'CGI::Util::' },
               'CGI::');

print_subs() is a B::GV method you have declared. Also see L<"B::GV
Methods">, below.

=back

=head2 Functions Returning C<B::OP> objects or for walking op trees

For descriptions of the class hierarchy of these objects and the
methods that can be called on them, see below, L<"OVERVIEW OF
CLASSES"> and L<"OP-RELATED CLASSES">.

=over 4

=item main_root

Returns the root op (i.e. an object in the appropriate B::OP-derived
class) of the main part of the Perl program.

=item main_start

Returns the starting op of the main part of the Perl program.

=item walkoptree(OP, METHOD)

Does a tree-walk of the syntax tree based at OP and calls METHOD on
each op it visits. Each node is visited before its children. If
C<walkoptree_debug> (see below) has been called to turn debugging on then
the method C<walkoptree_debug> is called on each op before METHOD is
called.

=item walkoptree_debug(DEBUG)

Returns the current debugging flag for C<walkoptree>. If the optional
DEBUG argument is non-zero, it sets the debugging flag to that. See
the description of C<walkoptree> above for what the debugging flag
does.

=back

=head2 Miscellaneous Utility Functions

=over 4

=item ppname(OPNUM)

Return the PP function name (e.g. "pp_add") of op number OPNUM.

=item hash(STR)

Returns a string in the form "0x..." representing the value of the
internal hash function used by perl on string STR.

=item cast_I32(I)

Casts I to the internal I32 type used by that perl.

=item minus_c

Does the equivalent of the C<-c> command-line option. Obviously, this
is only useful in a BEGIN block or else the flag is set too late.

=item cstring(STR)

Returns a double-quote-surrounded escaped version of STR which can
be used as a string in C source code.

=item perlstring(STR)

Returns a double-quote-surrounded escaped version of STR which can
be used as a string in Perl source code.

=item class(OBJ)

Returns the class of an object without the part of the classname
preceding the first C<"::">. This is used to turn C<"B::UNOP"> into
C<"UNOP"> for example.

=item threadsv_names

In a perl compiled for threads, this returns a list of the special
per-thread threadsv variables.

=back

=head2 Exported utility variabiles

=over 4

=item @optype

  my $op_type = $optype[$op_type_num];

A simple mapping of the op type number to its type (like 'COP' or 'BINOP').

=item @specialsv_name

  my $sv_name = $specialsv_name[$sv_index];

Certain SV types are considered 'special'.  They're represented by
B::SPECIAL and are referred to by a number from the specialsv_list.
This array maps that number back to the name of the SV (like 'Nullsv'
or '&PL_sv_undef').

=back


=head1 OVERVIEW OF CLASSES

The C structures used by Perl's internals to hold SV and OP
information (PVIV, AV, HV, ..., OP, SVOP, UNOP, ...) are modelled on a
class hierarchy and the C<B> module gives access to them via a true
object hierarchy. Structure fields which point to other objects
(whether types of SV or types of OP) are represented by the C<B>
module as Perl objects of the appropriate class.

The bulk of the C<B> module is the methods for accessing fields of
these structures.

Note that all access is read-only.  You cannot modify the internals by
using this module. Also, note that the B::OP and B::SV objects created
by this module are only valid for as long as the underlying objects
exist; their creation doesn't increase the reference counts of the
underlying objects. Trying to access the fields of a freed object will
give incomprehensible results, or worse.

=head2 SV-RELATED CLASSES

B::IV, B::NV, B::RV, B::PV, B::PVIV, B::PVNV, B::PVMG, B::BM (5.9.5 and
earlier), B::PVLV, B::AV, B::HV, B::CV, B::GV, B::FM, B::IO. These classes
correspond in the obvious way to the underlying C structures of similar names.
The inheritance hierarchy mimics the underlying C "inheritance". For 5.9.5
and later this is:

                           B::SV