B(3p) Perl Programmers Reference Guide B(3p) #
B(3p) Perl Programmers Reference Guide B(3p)
NNAAMMEE #
B - The Perl Compiler Backend
SSYYNNOOPPSSIISS #
use B;
DDEESSCCRRIIPPTTIIOONN #
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.
OOVVEERRVVIIEEWW #
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.
UUttiilliittyy FFuunnccttiioonnss 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.
FFuunnccttiioonnss RReettuurrnniinngg “"BB::::SSVV"”,, “"BB::::AAVV"”,, “"BB::::HHVV"”,, aanndd “"BB::::CCVV"” oobbjjeeccttss 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 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". As of Perl 5.18, this is just an alias to
"PL_na", so its value is meaningless.
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 PADLIST object (i.e. in class B::PADLIST) of the global
comppadlist. In Perl 5.16 and earlier it returns an AV object (class
B::AV). #
regex_padav
Only when perl was compiled with ithreads.
main_cv
Return the (faked) CV corresponding to the main part of the Perl
program.
FFuunnccttiioonnss ffoorr EExxaammiinniinngg tthhee SSyymmbbooll TTaabbllee 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::');
pprriinntt__ssuubbss(()) is a B::GV method you have declared. Also see "B::GV
Methods", below.
FFuunnccttiioonnss RReettuurrnniinngg “"BB::::OOPP"” oobbjjeeccttss oorr ffoorr wwaallkkiinngg oopp ttrreeeess 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.
MMiisscceellllaanneeoouuss UUttiilliittyy FFuunnccttiioonnss 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.
perlstring(STR)
Returns a double-quote-surrounded escaped version of STR which can be
used as a string in Perl source code.
safename(STR)
This function returns the string with the first character modified if
it is a control character. It converts it to ^X format first, so
that "\cG" becomes "^G". This is used internally by B::GV::SAFENAME,
but you can call it directly.
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
This used to provide support for the old 5.005 threading module. It
now does nothing.
EExxppoorrtteedd uuttiilliittyy vvaarriiaabblleess @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').
OOVVEERRVVIIEEWW OOFF CCLLAASSSSEESS #
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.
SSVV--RREELLAATTEEDD CCLLAASSSSEESS #
B::IV, B::NV, B::PV, B::PVIV, B::PVNV, B::PVMG, 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":
B::SV #
|
+------------+------------+
| | |
B::PV B::IV B::NV #
/ \ / /
/ \ / /
B::INVLIST 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").
BB::::SSVV MMeetthhooddss
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
ssvvrreeff__22oobbjjeecctt(()) 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.
BB::::IIVV MMeetthhooddss IV Returns the value of the IV, _i_n_t_e_r_p_r_e_t_e_d _a_s _a _s_i_g_n_e_d _i_n_t_e_g_e_r. 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
BB::::NNVV MMeetthhooddss
NV #
NVX #
COP_SEQ_RANGE_LOW #
COP_SEQ_RANGE_HIGH #
These last two are only valid for pad name SVs. They only existed in
the B::NV class before Perl 5.22. In 5.22 they were moved to the
B::PADNAME class.
BB::::RRVV MMeetthhooddss
RV #
BB::::PPVV MMeetthhooddss 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 ddiiee(()) 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 (CUR) is
overloaded for other purposes and can't be relied on here.
CUR This method returns the internal length field, which consists of the
number of internal bytes, not necessarily the number of logical
characters.
LEN This method returns the number of bytes allocated (via malloc) for
storing the string. This is 0 if the scalar does not "own" the
string.
BB::::PPVVMMGG MMeetthhooddss
MAGIC #
SvSTASH
BB::::MMAAGGIICC MMeetthhooddss
MOREMAGIC #
precomp
Only valid on r-magic, returns the string that generated the regexp.
PRIVATE #
TYPE #
FLAGS #
OBJ Will ddiiee(()) if called on r-magic.
PTR #
REGEX #
Only valid on r-magic, returns the integer value of the REGEX stored
in the MAGIC.
BB::::IINNVVLLIISSTT MMeetthhooddss prev_index Returns the cache result of previous iinnvvlliisstt__sseeaarrcchh(()) (internal usage)
is_offset
Returns a boolean value (0 or 1) to know if the invlist is using an
offset. When false the list begins with the code point U+0000. When
true the list begins with the following elements.
array_len
Returns an integer with the size of the array used to define the
invlist.
get_invlist_array
This method returns a list of integers representing the array used by
the invlist. Note: this cannot be used while in middle of iterating
on an invlist and croaks.
BB::::PPVVLLVV MMeetthhooddss
TARGOFF #
TARGLEN #
TYPE #
TARG #
BB::::BBMM MMeetthhooddss
USEFUL #
PREVIOUS #
RARE #
TABLE #
BB::::RREEGGEEXXPP MMeetthhooddss
REGEX #
precomp
qr_anoncv
compflags
The last two were added in Perl 5.22.
BB::::GGVV MMeetthhooddss 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 #
GPFLAGS #
This last one is present only in perl 5.22.0 and higher.
BB::::IIOO MMeetthhooddss B::IO objects derive from IO objects and you will get more information from the IO object itself.
For example:
$gvio = B::svref_2object(\*main::stdin)->IO;
$IO = $gvio->object_2svref();
$fd = $IO->fileno();
LINES #
PAGE #
PAGE_LEN #
LINES_LEFT #
TOP_NAME #
TOP_GV #
FMT_NAME #
FMT_GV #
BOTTOM_NAME #
BOTTOM_GV #
SUBPROCESS #
IoTYPE
A character symbolizing the type of IO Handle.
- STDIN/OUT #
I STDIN/OUT/ERR #
< read-only
> write-only
a append
+ read and write
s socket
| pipe
I IMPLICIT #
# NUMERIC #
space closed handle
\0 closed internal handle
IoFLAGS
IsSTD
Takes one argument ( '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)
== PPeerrllIIOO__ssttddeerrrr(()).
BB::::AAVV MMeetthhooddss
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.
BB::::CCVV MMeetthhooddss
STASH #
START #
ROOT #
GV #
FILE #
DEPTH #
PADLIST #
Returns a B::PADLIST object.
OUTSIDE #
OUTSIDE_SEQ #
XSUB #
XSUBANY #
For constant subroutines, returns the constant SV returned by the
subroutine.
CvFLAGS
const_sv
NAME_HEK #
Returns the name of a lexical sub, otherwise "undef".
BB::::HHVV MMeetthhooddss
FILL #
MAX #
KEYS #
RITER #
NAME #
ARRAY #
OOPP--RREELLAATTEEDD CCLLAASSSSEESS #
“B::OP”, “B::UNOP”, “B::UNOP_AUX”, “B::BINOP”, “B::LOGOP”, “B::LISTOP”, #
“B::PMOP”, “B::SVOP”, “B::PADOP”, “B::PVOP”, “B::LOOP”, “B::COP”, #
“B::METHOP”. #
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::METHOP #
|
+---+---+---------+
| | |
B::BINOP B::LOGOP B::UNOP_AUX #
|
|
B::LISTOP #
|
+---+---+
| |
B::LOOP B::PMOP #
Access methods correspond to the underlying C structure field names, with
the leading "class indication" prefix ("op_") removed.
BB::::OOPP MMeetthhooddss These methods get the values of similarly named fields within the OP data structure. See top of “op.h” for more info.
next
sibling
parent
Returns the OP's parent. If it has no parent, or if your perl wasn't
built with "-DPERL_OP_PARENT", returns NULL.
Note that the global variable $B::OP::does_parent is undefined on
older perls that don't support the "parent" method, is defined but
false on perls that support the method but were built without
"-DPERL_OP_PARENT", and is true otherwise.
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
opt
flags
private
spare
BB::::UUNNOOPP MMeetthhoodd first
BB::::UUNNOOPP__AAUUXX MMeetthhooddss ((ssiinnccee 55..2222)) aux_list(cv) This returns a list of the elements of the op’s aux data structure, or a null list if there is no aux. What will be returned depends on the object’s type, but will typically be a collection of “B::IV”, “B::GV”, etc. objects. “cv” is the “B::CV” object representing the sub that the op is contained within.
string(cv)
This returns a textual representation of the object (likely to b
useful for deparsing and debugging), or an empty string if the op
type doesn't support this. "cv" is the "B::CV" object representing
the sub that the op is contained within.
BB::::BBIINNOOPP MMeetthhoodd last
BB::::LLOOGGOOPP MMeetthhoodd other
BB::::LLIISSTTOOPP MMeetthhoodd children
BB::::PPMMOOPP MMeetthhooddss pmreplroot pmreplstart pmflags precomp pmoffset Only when perl was compiled with ithreads.
code_list
Since perl 5.17.1
pmregexp
Added in perl 5.22, this method returns the B::REGEXP associated with
the op. While PMOPs do not actually have "pmregexp" fields under
threaded builds, this method returns the regexp under threads
nonetheless, for convenience.
BB::::SSVVOOPP MMeetthhooddss sv gv
BB::::PPAADDOOPP MMeetthhoodd padix
BB::::PPVVOOPP MMeetthhoodd pv
BB::::LLOOOOPP MMeetthhooddss redoop nextop lastop
BB::::CCOOPP MMeetthhooddss The “B::COP” class is used for “nextstate” and “dbstate” ops. As of Perl 5.22, it is also used for “null” ops that started out as COPs.
label
stash
stashpv
stashoff (threaded only)
file
cop_seq
line
warnings
io
hints
hints_hash
BB::::MMEETTHHOOPP MMeetthhooddss ((SSiinnccee PPeerrll 55..2222)) first meth_sv
PPAADD--RREELLAATTEEDD CCLLAASSSSEESS #
Perl 5.18 introduced a new class, B::PADLIST, returned by B::CV's
"PADLIST" method.
Perl 5.22 introduced the B::PADNAMELIST and B::PADNAME classes.
BB::::PPAADDLLIISSTT MMeetthhooddss
MAX #
ARRAY #
A list of pads. The first one is a B::PADNAMELIST containing the
names. The rest are currently B::AV objects, but that could change
in future versions.
ARRAYelt
Like "ARRAY", but takes an index as an argument to get only one
element, rather than a list of all of them.
NAMES #
This method, introduced in 5.22, returns the B::PADNAMELIST. It is
equivalent to "ARRAYelt" with a 0 argument.
REFCNT #
id This method, introduced in 5.22, returns an ID shared by clones of
the same padlist.
outid
This method, also added in 5.22, returns the ID of the outer padlist.
BB::::PPAADDNNAAMMEELLIISSTT MMeetthhooddss
MAX #
ARRAY #
ARRAYelt
These two methods return the pad names, using B::SPECIAL objects for
null pointers and B::PADNAME objects otherwise.
REFCNT #
BB::::PPAADDNNAAMMEE MMeetthhooddss
PV #
PVX #
LEN #
REFCNT #
FLAGS #
For backward-compatibility, if the PADNAMEt_OUTER flag is set, the
FLAGS method adds the SVf_FAKE flag, too.
TYPE #
A B::HV object representing the stash for a typed lexical.
SvSTASH
A backward-compatibility alias for TYPE.
OURSTASH #
A B::HV object representing the stash for 'our' variables.
PROTOCV #
The prototype CV for a 'my' sub.
COP_SEQ_RANGE_LOW #
COP_SEQ_RANGE_HIGH #
Sequence numbers representing the scope within which a lexical is
visible. Meaningless if PADNAMEt_OUTER is set.
PARENT_PAD_INDEX #
Only meaningful if PADNAMEt_OUTER is set.
PARENT_FAKELEX_FLAGS #
Only meaningful if PADNAMEt_OUTER is set.
$$BB::::oovveerrllaayy Although the optree is read-only, there is an overlay facility that allows you to override what values the various B::*OP methods return for a particular op. $B::overlay should be set to reference a two-deep hash: indexed by OP address, then method name. Whenever a an op method is called, the value in the hash is returned if it exists. This facility is used by B::Deparse to “undo” some optimisations. For example:
local $B::overlay = {};
...
if ($op->name eq "foo") {
$B::overlay->{$$op} = {
name => 'bar',
next => $op->next->next,
};
}
...
$op->name # returns "bar"
$op->next # returns the next op but one
AAUUTTHHOORR #
Malcolm Beattie, "mbeattie@sable.ox.ac.uk"
perl v5.36.3 2023-02-15 B(3p)