Evalute if it's possibly to dump files directly from macOS dyld shared cache

[gabrielesvelto]

I noticed this PR that has been merged in gimli and I wonder if we could use the new functionality to dump macOS system libraries directly out of the dyld shared cache.

[mstange]

The dyld shared cache parsing code is in the object crate. We are currently using the symbolic-debuginfo crate to get symbols and unwind info from binaries, and that's using goblin and not object. But even if symbolic-debuginfo were using object, it would still need additional APIs to load an image from the shared cache: The shared cache spans multiple files (the root cache + 3-4 "subcaches") and it contains multiple images. So the API would need to be able to load an "archive" from multiple files, and then have a way to specify which "member" of that archive you want to load.

So that would be a bunch of extra work in the symbolic repo. It would also mean that symbolic would ship two binary parsers (goblin and object) unless every existing use of goblin gets migrated; alternatively, there would be a bunch of duplicated code to load symbols and unwind info from object.

Another alternative would be to make dump_syms use object directly, as an second source of symbols. And we'd need a way to get the ASCII CFI from the __unwind_info sections, and that code currently lives in symbolic. I'm not sure how easy the ASCII CFI dumper is to use with section data from object.