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If this is the book I recall seeing mentioned before, for a while, a number of years ago, it was considered both excellent and "hard to find."

Haven't read it. But thought I'd mention that, by way of sort of an indirect, old plug for it.

P.S. Correcting myself, my old memory: I seem to recall that one was called "Linkers and Loaders". Seems to be this?

Yes, Linkers and Loaders is an excellent book. There's also this 20 part linker essay by Ian Lance Taylor who went on to write gold:

And while gold is good, lld ups the bar even a little further.

Here's the site for Linkers and Loaders by John Levine:

There are links to chapters available on that site.