fixes bap.top and baptop #1541
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fixes bap.top and baptop #1541
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This commit fixes the `bap.top` library and the `baptop` executable so that they can now be used. Before that, they were failing with ``` Exception: (Invalid_argument "The dynlink.cma library cannot be used inside the OCaml toplevel") ``` The problem was that we were trying to use the dynlink facilities to track the missing units (before that we were using findlib for that so it was working). However, for toplevel we don't need to do this, as the toplevel loader will keep track of the loaded dependencies for us.
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After we switched to OCaml 4.08 and above, we trashed custom unit tracking from our plugin system and started to rely on the Dynlink facility, provided by OCaml, that offers precise unit tracking. However, Dynlink is not allowed inside OCaml Toplevel, which wasn't noticed, because it wasn't properly initialized (though apparently it worked fine for our needs). But after 4.12 (see ocaml/ocaml#9790) it was properly initialized so we started to get "The dynlink.cma library cannot be used inside the OCaml toplevel" messages when trying to use `baptop` or `bap.top`. A quick-fix (BinaryAnalysisPlatform#1541) did only worse as it disabled any unit tracking and enabled double-loading of plugins and libraries (which is perfectly allowed in OCaml toplevel and is not a bug, as it was in regular OCaml runtime). Of course, double-loading could crash bap as many of bap libraries have their own state, which got reset after reloading. This PR restores the old findlib-based unit tracker. This tracker is not precise and may still miss loaded units. For example, if you load bap manually and the do `#require "bap.top"` it will reload bap (which should be a problem, but who knows). With that said, we had used this tracker for many years, up until BAP 2.4.0, so I do have some trust in it. Also, I don't want to invest more time in this issue as we are in the process of switching to dune and thhe dune plugin system (that has its own unit tracking system, which is precise). To be honest, dune plugins also do not work in toplevel right now, but this is a developing story (ocaml/dune#6081) and I hope that eventually we will have it working.
ivg
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Aug 19, 2022
After we switched to OCaml 4.08 and above, we trashed custom unit tracking from our plugin system and started to rely on the Dynlink facility, provided by OCaml, that offers precise unit tracking. However, Dynlink is not allowed inside OCaml Toplevel, which wasn't noticed, because it wasn't properly initialized (though apparently it worked fine for our needs). But after 4.12 (see ocaml/ocaml#9790) it was properly initialized so we started to get "The dynlink.cma library cannot be used inside the OCaml toplevel" messages when trying to use `baptop` or `bap.top`. A quick-fix (#1541) did only worse as it disabled any unit tracking and enabled double-loading of plugins and libraries (which is perfectly allowed in OCaml toplevel and is not a bug, as it was in regular OCaml runtime). Of course, double-loading could crash bap as many of bap libraries have their own state, which got reset after reloading. This PR restores the old findlib-based unit tracker. This tracker is not precise and may still miss loaded units. For example, if you load bap manually and the do `#require "bap.top"` it will reload bap (which should be a problem, but who knows). With that said, we had used this tracker for many years, up until BAP 2.4.0, so I do have some trust in it. Also, I don't want to invest more time in this issue as we are in the process of switching to dune and thhe dune plugin system (that has its own unit tracking system, which is precise). To be honest, dune plugins also do not work in toplevel right now, but this is a developing story (ocaml/dune#6081) and I hope that eventually we will have it working.
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This commit fixes the
bap.toplibrary and thebaptopexecutable so that they can now be used. Before that, they were failing withThe problem was that we were trying to use the dynlink facilities to track the missing units (before that we were using findlib for that so it was working). However, for toplevel we don't need to do this, as the toplevel loader will keep track of the loaded dependencies for us.