I'm a little bit confused about line j, what means "rv2cv"?

I believe rv2cv gets the CV (code value, the code reference) from the specified glob (symbol table entry). Basically, foo() is implemented as something conceptually similar to *{"foo"}{CODE}->().

You'll find something similar for all other kinds of package variables: rv2sv for scalars, rv2av for arrays, rv2hv for hashes, etc.

>perl -MO=Concise -e"$s"
4  <@> leave[1 ref] vKP/REFC ->(end)
1     <0> enter ->2
2     <;> nextstate(main 1 -e:1) v ->3
-     <1> ex-rv2sv vK/1 ->4
3        <#> gvsv[*s] s ->4
-e syntax OK

>perl -MO=Concise -e"@a"
5  <@> leave[1 ref] vKP/REFC ->(end)
1     <0> enter ->2
2     <;> nextstate(main 1 -e:1) v ->3
4     <1> rv2av[t2] vK/1 ->5
3        <#> gv[*a] s ->4
-e syntax OK
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I'm a little bit confused about line j, what means "rv2cv"?

Opcodes are defined in pp*.c. Search for pp_opcode. pp_rv2cv is in pp.c.