


ext::B::B(3p)    Perl Programmers Reference Guide   ext::B::B(3p)


NAME
       B - The Perl Compiler

SYNOPSIS
               use B;

DESCRIPTION
       The "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 O module for the user-visible part. The "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.

OVERVIEW
       The "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.

Utility Functions
       The "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.

   Functions Returning "B::SV", "B::AV", "B::HV", and "B::CV"
       objects
       For descriptions of the class hierarchy of these objects
       and the methods that can be called on them, see below,
       "OVERVIEW OF CLASSES" and "SV-RELATED CLASSES".

       sv_undef
           Returns the SV object corresponding to the C variable
           "sv_undef".

       sv_yes
           Returns the SV object corresponding to the C variable
           "sv_yes".

       sv_no
           Returns the SV object corresponding to the C variable
           "sv_no".

       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



perl v5.10.1                2009-10-12                          1





ext::B::B(3p)    Perl Programmers Reference Guide   ext::B::B(3p)


           functions such as "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.

       amagic_generation
           Returns the SV object corresponding to the C variable
           "amagic_generation".

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

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

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

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

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

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

       regex_padav
           Only when perl was compiled with ithreads.

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

   Functions for Examining the Symbol Table
       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.



perl v5.10.1                2009-10-12                          2





ext::B::B(3p)    Perl Programmers Reference Guide   ext::B::B(3p)


           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 "B::GV Methods", below.

   Functions Returning "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,
       "OVERVIEW OF CLASSES" and "OP-RELATED CLASSES".

       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.

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

       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 "walkoptree_debug"
           (see below) has been called to turn debugging on then
           the method "walkoptree_debug" is called on each op
           before METHOD is called.

       walkoptree_debug(DEBUG)
           Returns the current debugging flag for "walkoptree".
           If the optional DEBUG argument is non-zero, it sets
           the debugging flag to that. See the description of
           "walkoptree" above for what the debugging flag does.

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

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

       cast_I32(I)
           Casts I to the internal I32 type used by that perl.

       minus_c
           Does the equivalent of the "-c" command-line option.
           Obviously, this is only useful in a BEGIN block or



perl v5.10.1                2009-10-12                          3





ext::B::B(3p)    Perl Programmers Reference Guide   ext::B::B(3p)


           else the flag is set too late.

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

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

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

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

   Exported utility variabiles
       @optype
             my $op_type = $optype[$op_type_num];

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

       @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').

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 "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 "B" module as Perl
       objects of the appropriate class.

       The bulk of the "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.



perl v5.10.1                2009-10-12                          4





ext::B::B(3p)    Perl Programmers Reference Guide   ext::B::B(3p)


   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 the 5.10.x branch, (ie 5.10.0, 5.10.1
       etc) this is:

                                  B::SV
                                    |
                       +------------+------------+------------+
                       |            |            |            |
                     B::PV        B::IV        B::NV        B::RV
                         \         /           /
                          \       /           /
                           B::PVIV           /
                                \           /
                                 \         /
                                  \       /
                                   B::PVNV
                                      |
                                      |
                                   B::PVMG
                                      |
                          +-----+-----+-----+-----+
                          |     |     |     |     |
                        B::AV B::GV B::HV B::CV B::IO
                                |           |
                                |           |
                             B::PVLV      B::FM

       For 5.9.0 and earlier, PVLV is a direct subclass of PVMG,
       and BM is still present as a distinct type, so the base of
       this diagram is

                                      |
                                      |
                                   B::PVMG
                                      |
                   +------+-----+-----+-----+-----+-----+
                   |      |     |     |     |     |     |
                B::PVLV B::BM B::AV B::GV B::HV B::CV B::IO
                                                  |
                                                  |
                                                B::FM

       For 5.11.0 and later, B::RV is abolished, and IVs can be
       used to store references, and a new type B::REGEXP is
       introduced, giving this structure:







perl v5.10.1                2009-10-12                          5





ext::B::B(3p)    Perl Programmers Reference Guide   ext::B::B(3p)


                                  B::SV
                                    |
                       +------------+------------+
                       |            |            |
                     B::PV        B::IV        B::NV
                         \         /           /
                          \       /           /
                           B::PVIV           /
                                \           /
                                 \         /
                                  \       /
                                   B::PVNV
                                      |
                                      |
                                   B::PVMG
                                      |
                  +-------+-------+---+---+-------+-------+
                  |       |       |       |       |       |
                B::AV   B::GV   B::HV   B::CV   B::IO B::REGEXP
                          |               |
                          |               |
                       B::PVLV          B::FM

       Access methods correspond to the underlying C macros for
       field access, usually with the leading "class indication"
       prefix removed (Sv, Av, Hv, ...). The leading prefix is
       only left in cases where its removal would cause a clash
       in method name. For example, "GvREFCNT" stays as-is since
       its abbreviation would clash with the "superclass" method
       "REFCNT" (corresponding to the C function "SvREFCNT").

   B::SV Methods
       REFCNT
       FLAGS
       object_2svref
           Returns a reference to the regular scalar
           corresponding to this B::SV object. In other words,
           this method is the inverse operation to the
           svref_2object() subroutine. This scalar and other data
           it points at should be considered read-only: modifying
           them is neither safe nor guaranteed to have a sensible
           effect.

   B::IV Methods
       IV  Returns the value of the IV, interpreted as a signed
           integer. This will be misleading if "FLAGS &
           SVf_IVisUV". Perhaps you want the "int_value" method
           instead?

       IVX
       UVX
       int_value
           This method returns the value of the IV as an integer.
           It differs from "IV" in that it returns the correct



perl v5.10.1                2009-10-12                          6





ext::B::B(3p)    Perl Programmers Reference Guide   ext::B::B(3p)


           value regardless of whether it's stored signed or
           unsigned.

       needs64bits
       packiv

   B::NV Methods
       NV
       NVX

   B::RV Methods
       RV

   B::PV Methods
       PV  This method is the one you usually want. It constructs
           a string using the length and offset information in
           the struct: for ordinary scalars it will return the
           string that you'd see from Perl, even if it contains
           null characters.

       RV  Same as B::RV::RV, except that it will die() if the PV
           isn't a reference.

       PVX This method is less often useful. It assumes that the
           string stored in the struct is null-terminated, and
           disregards the length information.

           It is the appropriate method to use if you need to get
           the name of a lexical variable from a padname array.
           Lexical variable names are always stored with a null
           terminator, and the length field (SvCUR) is overloaded
           for other purposes and can't be relied on here.

   B::PVMG Methods
       MAGIC
       SvSTASH

   B::MAGIC Methods
       MOREMAGIC
       precomp
           Only valid on r-magic, returns the string that
           generated the regexp.

       PRIVATE
       TYPE
       FLAGS
       OBJ Will die() if called on r-magic.

       PTR
       REGEX
           Only valid on r-magic, returns the integer value of
           the REGEX stored in the MAGIC.





perl v5.10.1                2009-10-12                          7





ext::B::B(3p)    Perl Programmers Reference Guide   ext::B::B(3p)


   B::PVLV Methods
       TARGOFF
       TARGLEN
       TYPE
       TARG

   B::BM Methods
       USEFUL
       PREVIOUS
       RARE
       TABLE

   B::GV Methods
       is_empty
           This method returns TRUE if the GP field of the GV is
           NULL.

       NAME
       SAFENAME
           This method returns the name of the glob, but if the
           first character of the name is a control character,
           then it converts it to ^X first, so that *^G would
           return "^G" rather than "\cG".

           It's useful if you want to print out the name of a
           variable.  If you restrict yourself to globs which
           exist at compile-time then the result ought to be
           unambiguous, because code like "${"^G"} = 1" is
           compiled as two ops - a constant string and a
           dereference (rv2gv) - so that the glob is created at
           runtime.

           If you're working with globs at runtime, and need to
           disambiguate *^G from *{"^G"}, then you should use the
           raw NAME method.

       STASH
       SV
       IO
       FORM
       AV
       HV
       EGV
       CV
       CVGEN
       LINE
       FILE
       FILEGV
       GvREFCNT
       FLAGS

   B::IO Methods
       LINES




perl v5.10.1                2009-10-12                          8





ext::B::B(3p)    Perl Programmers Reference Guide   ext::B::B(3p)


       PAGE
       PAGE_LEN
       LINES_LEFT
       TOP_NAME
       TOP_GV
       FMT_NAME
       FMT_GV
       BOTTOM_NAME
       BOTTOM_GV
       SUBPROCESS
       IoTYPE
       IoFLAGS
       IsSTD
           Takes one arguments ( 'stdin' | 'stdout' | 'stderr' )
           and returns true if the IoIFP of the object is equal
           to the handle whose name was passed as argument ( i.e.
           $io->IsSTD('stderr') is true if IoIFP($io) ==
           PerlIO_stdin() ).

   B::AV Methods
       FILL
       MAX
       ARRAY
       ARRAYelt
           Like "ARRAY", but takes an index as an argument to get
           only one element, rather than a list of all of them.

       OFF This method is deprecated if running under Perl 5.8,
           and is no longer present if running under Perl 5.9

       AvFLAGS
           This method returns the AV specific flags. In Perl 5.9
           these are now stored in with the main SV flags, so
           this method is no longer present.

   B::CV Methods
       STASH
       START
       ROOT
       GV
       FILE
       DEPTH
       PADLIST
       OUTSIDE
       OUTSIDE_SEQ
       XSUB
       XSUBANY
           For constant subroutines, returns the constant SV
           returned by the subroutine.

       CvFLAGS
       const_sv





perl v5.10.1                2009-10-12                          9





ext::B::B(3p)    Perl Programmers Reference Guide   ext::B::B(3p)


   B::HV Methods
       FILL
       MAX
       KEYS
       RITER
       NAME
       ARRAY
       PMROOT
           This method is not present if running under Perl 5.9,
           as the PMROOT information is no longer stored directly
           in the hash.

   OP-RELATED CLASSES
       "B::OP", "B::UNOP", "B::BINOP", "B::LOGOP", "B::LISTOP",
       "B::PMOP", "B::SVOP", "B::PADOP", "B::PVOP", "B::LOOP",
       "B::COP".

       These classes correspond in the obvious way to the
       underlying C structures of similar names. The inheritance
       hierarchy mimics the underlying C "inheritance":

                                        B::OP
                                          |
                          +---------------+--------+--------+-------+
                          |               |        |        |       |
                       B::UNOP          B::SVOP B::PADOP  B::COP  B::PVOP
                        ,'  `-.
                       /       `--.
                  B::BINOP     B::LOGOP
                      |
                      |
                  B::LISTOP
                    ,' `.
                   /     \
               B::LOOP B::PMOP

       Access methods correspond to the underlying C structre
       field names, with the leading "class indication" prefix
       ("op_") removed.

   B::OP Methods
       These methods get the values of similarly named fields
       within the OP data structure.  See top of "op.h" for more
       info.

       next
       sibling
       name
           This returns the op name as a string (e.g. "add",
           "rv2av").

       ppaddr
           This returns the function name as a string (e.g.
           "PL_ppaddr[OP_ADD]", "PL_ppaddr[OP_RV2AV]").



perl v5.10.1                2009-10-12                         10





ext::B::B(3p)    Perl Programmers Reference Guide   ext::B::B(3p)


       desc
           This returns the op description from the global C
           PL_op_desc array (e.g. "addition" "array deref").

       targ
       type
       opt
       flags
       private
       spare

   B::UNOP METHOD
       first

   B::BINOP METHOD
       last

   B::LOGOP METHOD
       other

   B::LISTOP METHOD
       children

   B::PMOP Methods
       pmreplroot
       pmreplstart
       pmnext
           Only up to Perl 5.9.4

       pmregexp
       pmflags
       extflags
           Since Perl 5.9.5

       precomp
       pmoffset
           Only when perl was compiled with ithreads.

   B::SVOP METHOD
       sv
       gv

   B::PADOP METHOD
       padix

   B::PVOP METHOD
       pv

   B::LOOP Methods
       redoop
       nextop
       lastop





perl v5.10.1                2009-10-12                         11





ext::B::B(3p)    Perl Programmers Reference Guide   ext::B::B(3p)


   B::COP Methods
       label
       stash
       stashpv
       file
       cop_seq
       arybase
       line
       warnings
       io
       hints
       hints_hash

AUTHOR
       Malcolm Beattie, "mbeattie@sable.ox.ac.uk"










































perl v5.10.1                2009-10-12                         12


