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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 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.

SV-RELATED CLASSES

B::IV, B::NV, B::RV, B::PV, B::PVIV, B::PVNV, B::PVMG, B::BM, 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". 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

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 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.

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
PRIVATE
TYPE
FLAGS
OBJ
PTR

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
PAGE
PAGE_LEN
LINES_LEFT
TOP_NAME
TOP_GV
FMT_NAME
FMT_GV
BOTTOM_NAME
BOTTOM_GV
SUBPROCESS
IoTYPE
IoFLAGS

B::AV METHODS

FILL
MAX
OFF
ARRAY
AvFLAGS

B::CV METHODS

STASH
START
ROOT
GV
FILE
DEPTH
PADLIST
OUTSIDE
XSUB
XSUBANY
CvFLAGS
const_sv

B::HV METHODS

FILL
MAX
KEYS
RITER
NAME
PMROOT
ARRAY

OP-RELATED CLASSES

B::OP, B::UNOP, B::BINOP, B::LOGOP, B::LISTOP, B::PMOP, B::SVOP, B::PADOP, B::PVOP, B::CVOP, 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". Access methods correspond to the underlying C structre field names, with the leading "class indication" prefix removed (op_).

B::OP METHODS

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]").

desc

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

targ
type
seq
flags
private

B::UNOP METHOD

first

B::BINOP METHOD

last

B::LOGOP METHOD

other

B::LISTOP METHOD

children

B::PMOP METHODS

pmreplroot
pmreplstart
pmnext
pmregexp
pmflags
pmpermflags
precomp

B::SVOP METHOD

sv
gv

B::PADOP METHOD

padix

B::PVOP METHOD

pv

B::LOOP METHODS

redoop
nextop
lastop

B::COP METHODS

label
stash
file
cop_seq
arybase
line

FUNCTIONS EXPORTED BY B ^

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.

main_cv

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

init_av

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

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.

comppadlist

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

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.

amagic_generation

Returns the SV object corresponding to the C variable amagic_generation.

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 (q.v.) 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.

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.
  # Only recurse into CGI::Util::
  walksymtable(\%CGI::, 'print_subs', sub { $_[0] eq 'CGI::Util::' },
               'CGI::');

print_subs() is a B::GV method you have declared.

svref_2object(SV)

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

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 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.

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.

AUTHOR ^

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

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