Provide cross-compile $auto library support

[joelgallant]

Currently, cargo-deb uses ldd statically, which will not work on a non-native target arch. The behavior of this could be emulated, as far as I'm aware.

I'd be open to help work on this with some guidance on best steps.

[kornelski]

Yeah, support for deps in cross-compilation would be great. What does it require?

[joelgallant]

If I understand cargo-deb's usage of ldd at the moment, it could be emulated with the target-specific readelf, grep for Shared library, pass those into locate, pass that into dpkg -S to find the apt package source? I'm not confident that that's a robust mechanism, but it's probably the same as the ldd method there is now.

[ludiazv]

I run cargo deb inside docker image of the target machine. For example if I'm packing for a arm64 i use a image using arm64v8/rust:1.43-slim-buster base image. Cargo deb runs target arch and should resolve the correct dependencies.

[kornelski]

Using readelf seems like doing it "the hard way". I hoped there would be something like cross-arch version of ldd and/or a flag in dpkg to look for a different arch.

[gabrik]

Any update on this?

Can't rely on readelf or objdump for discovery the dependencies instead of ldd?

I guess readelf or objdump can be specified for each architecture in the ./cargo/config.toml

We are running our build in a Jenkins that already uses a container, therefore we cannot spawn another container just for the .deb generation.

[kornelski]

I'm not working on this. It probably won't be done.

[gabrik]

I can try to give it some time.
Once I have something working I'll do a PR.

[kornelski]

That would be great, thanks.

Maybe you could use a Rust elf parsing library instead of shelling out to readelf/objdump?

[H-M-H]

I just stumbled across this trying to fix another issue. I had a look at the linked elf parser and implemented a function that extracts the needed shared libs: #170 (comment)
This only returns the names of those libs, not a path to their location. But one still could use dpkg -S to locate the required packages as it does not only include exact matches. So some more filtering of the result of dpkg -S probably needs to be done. Alternatively if not cross compiling, using ldd to find the exact library path will still work. Additionally a look at apt-file may be worth it as it does not require packages to be installed to search for matching files.

[ryankurte]

there's a wee interaction with cross here too (related to #99), if you compile in cross then run cargo deb outside of cross the $auto deps seem to resolve incorrectly, which not hugely surprising because it's a different ldd...

not sure there's a reasonable way to fix it, but it's easy-ish to manually specify the deps to avoid the problem. i figured i'd post here in case it helps someone else in the same basket.