perlguts.pod

Message-ID: <20001210000647.A16203@deep-dark-truthful-mirror.perlhacker.org>

Documentation of the different types of ops,
plus the functions in dump.c

p4raw-id: //depot/perl@8063

1 files changed, 60 insertions, 0 deletions

diff --git a/pod/perlguts.pod b/pod/perlguts.pod
index ded9191923..f38bba37a0 100644
--- a/pod/perlguts.pod
+++ b/pod/perlguts.pod
@@ -1515,6 +1515,31 @@ The execution order is indicated by C<===E<gt>> marks, thus it is C<3
 4 5 6> (node C<6> is not included into above listing), i.e.,
 C<gvsv gvsv add whatever>.
 
+Each of these nodes represents an op, a fundamental operation inside the
+Perl core. The code which implements each operation can be found in the
+F<pp*.c> files; the function which implements the op with type C<gvsv>
+is C<pp_gvsv>, and so on. As the tree above shows, different ops have
+different numbers of children: C<add> is a binary operator, as one would
+expect, and so has two children. To accommodate the various different
+numbers of children, there are various types of op data structure, and
+they link together in different ways.
+
+The simplest type of op structure is C<OP>: this has no children. Unary
+operators, C<UNOP>s, have one child, and this is pointed to by the
+C<op_first> field. Binary operators (C<BINOP>s) have not only an
+C<op_first> field but also an C<op_last> field. The most complex type of
+op is a C<LISTOP>, which has any number of children. In this case, the
+first child is pointed to by C<op_first> and the last child by
+C<op_last>. The children in between can be found by iteratively
+following the C<op_sibling> pointer from the first child to the last.
+
+There are also two other op types: a C<PMOP> holds a regular expression,
+and has no children, and a C<LOOP> may or may not have children. If the
+C<op_children> field is non-zero, it behaves like a C<LISTOP>. To
+complicate matters, if a C<UNOP> is actually a C<null> op after
+optimization (see L</Compile pass 2: context propagation>) it will still
+have children in accordance with its former type.
+
 =head2 Compile pass 1: check routines
 
 The tree is created by the compiler while I<yacc> code feeds it
@@ -1575,6 +1600,41 @@ additional complications for conditionals).  These optimizations are
 done in the subroutine peep().  Optimizations performed at this stage
 are subject to the same restrictions as in the pass 2.
 
+=head1 Examining internal data structures with the C<dump> functions
+
+To aid debugging, the source file F<dump.c> contains a number of
+functions which produce formatted output of internal data structures.
+
+The most commonly used of these functions is C<Perl_sv_dump>; it's used
+for dumping SVs, AVs, HVs, and CVs. The C<Devel::Peek> module calls
+C<sv_dump> to produce debugging output from Perl-space, so users of that
+module should already be familiar with its format. 
+
+C<Perl_op_dump> can be used to dump an C<OP> structure or any of its
+derivatives, and produces output similiar to C<perl -Dx>; in fact,
+C<Perl_dump_eval> will dump the main root of the code being evaluated,
+exactly like C<-Dx>.
+
+Other useful functions are C<Perl_dump_sub>, which turns a C<GV> into an
+op tree, C<Perl_dump_packsubs> which calls C<Perl_dump_sub> on all the
+subroutines in a package like so: (Thankfully, these are all xsubs, so
+there is no op tree)
+
+    (gdb) print Perl_dump_packsubs(PL_defstash)
+
+    SUB attributes::bootstrap = (xsub 0x811fedc 0)
+
+    SUB UNIVERSAL::can = (xsub 0x811f50c 0)
+
+    SUB UNIVERSAL::isa = (xsub 0x811f304 0)
+
+    SUB UNIVERSAL::VERSION = (xsub 0x811f7ac 0)
+
+    SUB DynaLoader::boot_DynaLoader = (xsub 0x805b188 0)
+
+and C<Perl_dump_all>, which dumps all the subroutines in the stash and
+the op tree of the main root.
+
 =head1 How multiple interpreters and concurrency are supported
 
 =head2 Background and PERL_IMPLICIT_CONTEXT