Where does the list of required shared libraries come from?

[ole]

Hi Toni, great project! I found it through your post on the Swift forums.

I modified your project to write my own little function. Since my function uses Swift 5 features, I switched the Docker image to codevapor/swift:5.0.

Everything seemed to work, but when I tested my function on AWS, it failed with:

error while loading shared libraries: libswiftDispatch.so: cannot open shared object file: No such file or directory

It looks like the source of this error is that the names of one or more shared libraries changed in Swift 5, e.g. libdispatch.so is now called libswiftDispatch.so. So I need to update the list of shared libraries in the Makefile. Can I ask how you generated this list?

Running ldd [path_to_my_binary] on Linux seems to be an option to get a list of the shared libraries loaded by an executable, but I wanted to ask if you used a different option.

Thanks and happy holidays!

PS: Don't let me stop you from enjoying your holidays. This isn't urgent.

[tonisuter]

Hi Ole

Thank you :-)! That's a good question.

I tried several things. First, I tried to statically link the standard library using swiftc's -static-stdlib flag. This works fine when the program only uses the standard library. However, it doesn't work on Linux when the program imports Foundation due to a bug (see SR-2205).

So I created a very simple Swift executable in a swift:latest Docker container that just imports Foundation and prints the current date. I used the ldd command to get a list of the shared libraries that the executable uses (see Stackoverflow):

$ docker run --rm -it swift /bin/bash
root@0f4fa22b3c5f:/# mkdir TestPkg
root@0f4fa22b3c5f:/# cd TestPkg
root@0f4fa22b3c5f:/TestPkg# swift package init --type executable
root@0f4fa22b3c5f:/TestPkg# echo "import Foundation" > Sources/TestPkg/main.swift
root@0f4fa22b3c5f:/TestPkg# echo "print(Date())" >> Sources/TestPkg/main.swift
root@0f4fa22b3c5f:/TestPkg# swift build
root@0f4fa22b3c5f:/TestPkg# ldd .build/debug/TestPkg | sed -e 's/\t//' | sed -e 's/.*=..//' | sed -e 's/ (0.*)//' | sort

On AWS, I then tried to execute the lambda while setting the library search path to a directory that contains all of those shared libraries like this:

LD_LIBRARY_PATH=./shared-libs ./lambda

That didn't work due to a relocation error. Thanks to this repository I figured out that I can execute the lambda through the dynamic linker (i.e., the ld-linux-x86-64.so.2 file) which somehow solves the relocation error. This is what I'm now doing in the bootstrap file and it seems to work quite well.

I hope this helps. Happy holidays to you, too!

[ole]

Thanks @tonisuter, that's very helpful. I'll try again and report back.

[ole]

Copying the list produced by ldd into the Makefile worked, so I can confirm (unsurprisingly) the process also works with the current Swift 5 prerelease using the codevapor/swift:5.0 Docker image. Thanks again for the help.