|
|
| |
B(3) |
Perl Programmers Reference Guide |
B(3) |
B - The Perl Compiler Backend
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.
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.
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.
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.
- 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 "B::GV Methods", below.
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.
- 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.
- @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').
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.
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").
- 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.
- 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
- 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.
- 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 (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.
- 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.
- prev_index
- Returns the cache result of previous invlist_search() (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.
- TARGOFF
- TARGLEN
- TYPE
- TARG
- USEFUL
- PREVIOUS
- RARE
- TABLE
- REGEX
- precomp
- qr_anoncv
- compflags
- The last two were added in Perl 5.22.
- 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.
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) == PerlIO_stderr().
- 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.
- 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".
- FILL
- MAX
- KEYS
- RITER
- NAME
- ARRAY
"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.
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
- 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.
- 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.
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
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.
- 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.
- MAX
- ARRAY
- ARRAYelt
- These two methods return the pad names, using B::SPECIAL objects for null
pointers and B::PADNAME objects otherwise.
- REFCNT
- 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.
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
Malcolm Beattie, "mbeattie@sable.ox.ac.uk"
Visit the GSP FreeBSD Man Page Interface. Output converted with ManDoc. |