Not quite. It seems to give the line number where the subroutine becomes known to perl. Thus, if the sub is used before it is defined the line numbers will be wrong. Example:

#!/usr/bin/perl
use 5.010;
say f( 34 );

sub f {
  $_[0] + 8
}
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Then, perl -MO=Xref,d /tmp/test.pl gives (among other things):

    Package main
      &f                s3
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Which is the line where f is used, not defined.

This is perl, v5.10.1 (*) built for x86_64-linux-gnu-thread-multi
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