How do package body initializers get run in GNU Ada?

[Van Snyder <vsnyder@math.jpl.nasa.gov>]

In GNU Ada, what mechanism is used to cause execution of package
body initializers, i.e., the code between begin and end in a
package body?

Is it done using some kind of back-patching/overlaying done
by an otherwise garden-variety ld, by special features added
to ld to support Ada, by first-time flags at the entries
to procedures, or by something else?

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