Shared/static libraries in static-program-op context

[Luís Oliveira]

Hello Florian,

On Sun, 24 May 2020 at 20:58, Florian Margaine <florian at margaine.com> wrote:
> - CFFI loads a static foreign library, either as :grovel-wrapper or :system
> - The image is dumped with the loaded library
> - When restored, the runtime will try to reload those "shared" libraries and fails because the path doesn't exist on the target system

Let me point out, that this is an issue for regular foreign libraries.
Take cl-sqlite as an example:

(define-foreign-library sqlite3-lib
  (:darwin (:default "libsqlite3"))
  (:unix (:or "libsqlite3.so.0" "libsqlite3.so"))
  (t (:or (:default "libsqlite3") (:default "sqlite3"))))

On UNIX, (load-foreign-library 'sqlite3-lib) will attempt to load
"lbsqlite3.so.0" first. If that fails, "libsqlite3.so" will be used
instead. Whichever happens to succeed when building an image, is what
will be retried when starting up the image. Things get worse if things
like *foreign-library-directories* come into play. When that's used,
the library will be loaded using an absolute path, and that's what
will be retried at startup.

The proper way to handle this is to close all foreign libraries before
dumping an image, and reload them using load-foreign-library at
startup.

I think we should either (a) have load-foreign-library register these
hooks or (b) somehow hook into image/runtime-op (not the static
versions) to perform this unload/reload dance.

We might have to be mindful that people shipping applications most
likely do this dance themselves, so we might clash. For instance, we
could offer this functionality as a convenient hook users can use in
their dump and startup routines.


> Specifically for the 2nd one, CFFI provides a :c-file ASDF integration, which, when used with :static-program-op, will compile the C file into an object file (among others), load it as a foreign library, and statically link the object file with the program.

For :c-file, when shipped dynamically, I think the best we can do is
make sure it's reloaded by name instead of absolute path. That'd work
on Windows, by placing the DLL next to the executable. Not sure what
the proper way would be on UNIX.

For a statically linked :c-file (or wrapper, or whatever), then we of
course need to avoid reopening.

I conclude that we /always/ want to close on dump. Should we just do
that unconditionally?

As for reloading, we'd still need to distinguish between what should
and shouldn't be reloaded, so I'm leaning towards your CLOSE-ON-DUMP
idea but call it RELOAD-ON-RESTART (or something along those lines).
Why do you say it implies exposing REGISTER-FOREIGN-LIBRARY? Seems
like a LOAD-FOREIGN-LIBRARY option, no?

Cheers,

-- 
Luís Oliveira
http://kerno.org/~luis/