${ caller()."::meta" } = 1;
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Caveat: Assumes the calling package and the package in which the sub was compiled is the same, so the following won't work:

package pkg3;

sub foo { print "$_[0]: meta=$meta;\n"; };

package pkg2;

pkg1::test1(\&pkg3::foo);
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$_, $a and $b are usually used since strict doesn't complain about them. $_ is truly global, but $a and $b require using caller as above.