$ gdb --args ./perl -e 'my *x'
...
(gdb) br Perl_newGVREF
Breakpoint 1 at 0x80a51e2: file op.c, line 4905.
(gdb) run
Starting program: /local/build/perl-current/perl -e my\ \*x
...
Breakpoint 1, Perl_newGVREF (my_perl=0x81b07c0, type=0, o=0x81ccc50)
  at op.c:4905
4905        if (o->op_type == OP_PADANY) {
(gdb) p *o
$1 = {op_next = 0x81ccc50, op_sibling = 0x0, 
  op_ppaddr = 0x80e2c0c <Perl_pp_const>, op_targ = 0, op_type = 5, op_opt = 0, 
  op_static = 0, op_spare = 0, op_flags = 2 '\002', op_private = 16 '\020'}