perl-compiler/ramblings/blogs-debugging-article3.pod

In the first B::C debugging article we stepped into the B::C comnpiler with Od.
In the second B::C debugging article we stepped the c code with gdb.
We saw that the compiler is missing a sub in a seperate package, the most a typical 
problem with the compiler.

We have a cool workaround for this, the -u option. 
<b>-udummy<b> forces all symbols in the package dummy to be dumped.

<tt>'package dummy;sub meth{print "ok"};package main;dummy->meth'</tt> as ccode35.pl

<pre>
$ <b>perl -MO=C,-Do,-v,-udummy,-occode35.c ccode35.pl</b>

Starting compile
Walking tree
walkoptree: 0. LISTOP (0x1471a20) leave
walkoptree: 1. OP (0x1471a48) enter
walkoptree: 1. COP (0x14719e0) nextstate
walkoptree: 1. UNOP (0x1471998) entersub
walkoptree: 2. OP (0x14719c0) pushmark
walkoptree: 2. SVOP (0x1472000) const
walkoptree: 2. SVOP (0x1471978) method_named
done main optree, walking symtable for extras
Prescan for unused subs
Saving unused subs
walkoptree: 0. UNOP (0x164a6c0) leavesub
walkoptree: 1. LISTOP (0x164a698) lineseq
walkoptree: 2. COP (0x1472a00) nextstate
walkoptree: 2. LISTOP (0x1472d48) print
walkoptree: 3. OP (0x1523598) pushmark
walkoptree: 3. SVOP (0x147fad8) const
save context:
curpad names:
curpad syms:
%INC and @INC:
amagic_generation = 1
Writing output
Total number of OPs processed: 13
NULLOP count: 0
Loaded Cwd
Loaded B
Loaded IO
Loaded Fcntl
Loaded B::C
ccode35.pl syntax OK
</pre>

Here it is!
0. UNOP (0x164a6c0) leavesub
1. LISTOP (0x164a698) lineseq
2. COP (0x1472a00) nextstate
2. LISTOP (0x1472d48) print
3. OP (0x1523598) pushmark
3. SVOP (0x147fad8) const

is indeed our missing &dummy::meth

$ perl -MO=Concise,dummy::meth ccode35.pl
dummy::meth:
5  <1> leavesub[1 ref] K/REFC,1 ->(end)
-     <@> lineseq KP ->5
1        <;> nextstate(dummy 1 ccode35.pl:1) v ->2
4        <@> print sK ->5
2           <0> pushmark s ->3
3           <$> const(PV "ok") s ->4

Any sub argument to B::Concise dumps the optree for this sub, not just main.