B - The Perl Compiler
use B;
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 hierachy 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. 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. 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.
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 hierachy 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. 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.
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.
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:
B::SV | +--------------+----------------------+ | | | B::PV B::IV B::RV | \ / \ | \ / \ | B::PVIV B::NV \ / \____ __/ \ / B::PVNV | | B::PVMG | +------+-----+----+------+-----+-----+ | | | | | | | B::PVLV B::BM B::AV B::GV B::HV B::CV B::IO | | B::FMAccess 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
RV
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.
MAGIC SvSTASH
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.
TARGOFF TARGLEN TYPE TARG
USEFUL PREVIOUS RARE TABLE
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
LINES 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() ).
FILL MAX OFF ARRAY ARRAYelt Like ARRAY, but takes an index as an argument to get only one element, rather than a list of all of them. AvFLAGS
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
FILL MAX KEYS RITER NAME PMROOT ARRAY
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::BINOP B::LOGOP | | B::LISTOP ,’ ‘. / \ B::LOOP B::PMOPAccess methods correspond to the underlying C structre field names, with the leading class indication prefix ("op_") removed.
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
first
last
other
children
pmreplroot pmreplstart pmnext pmregexp pmflags pmdynflags pmpermflags precomp pmoffset Only when perl was compiled with ithreads.
sv gv
padix
pv
redoop nextop lastop
label stash stashpv file cop_seq arybase line warnings io
Malcolm Beattie, mbeattie@sable.ox.ac.uk
| perl v5.8.5 | B (3pm) | 2001-09-21 |