In my recent development of my first Vapor service, I settled on a workflow for deployment that involves using the Swift Docker image to build my app, then copying the built product to an Ubuntu Docker image to run. This is nice because it prevents my server from needing a compiler on it, but I can’t help but notice the inefficiency of using Docker to compile when I have a desktop Mac sitting here ready to do it.
Cross-compiling is nothing new, but is there a way to configure macOS’ Swift compiler to do this, assuming I would be able to download all of the Linux headers that I would need?
It is supposed to be possible for the main development branch, and some people use it that way. But it hasn’t been officially supported in any release and remains undocumented. Nor is it tested very well (if at all), so it tends to end up broken from time to time.
That said, you could look at the original pull request to SwiftPM, which is rather old, but includes examples specifically for the macOS‐to‐Ubuntu scenario. You could also compare my more recent script for cross‐compiling for Android. It targets a different platform, but it serves as a more modern demonstration of what you’ll need and how you’ll need to use it.
But you should know that the it won’t be nearly as easy as using Docker, which also has the benefit of official support and thorough testing. For most developers wanting to compile for Ubuntu from macOS, the Docker method is what I would recommend.
@0xTim
I tried it. It did generate the binary for linux (ubuntu.) But when I run it on linux, I get the error: error while loading shared libraries: libswiftSwiftOnoneSupport.so: cannot open shared object file: No such file or directory.
That could be an issue with the RUNPATH embedded in the executable not pointing to the directory where the swift libraries reside. See what the output of readelf -aW <executable>|grep RUNPATH shows.
The libraries are normally in the subdirectory usr/lib/swift/linux/ where the tar file was untarred so you could try running the executable with LD_LIBRARY_PATH=<swift install dir>/usr/lib/swift/linux <executable>
@spevans
On the linux box, the output of readelf -aW bm | grep RUNPATH is: Library runpath: [/usr/lib/swift/linux:/usr/lib/swift:$ORIGIN].
When you say run with LD_LIBRARY_PATH=<swift install dir>/usr/lib/swift/linux <executable> -- there's no swift on the linux box. Will I need to install swift on the linux machine to run the binary?
Yes you will need swift to be installed on the Ubunutu host as your executable needs to load the shared libraries. Try downloading the same version of swift you compiled against and untar it into the / directory
You only need to supply the necessary shared libraries alongside your executable. Those are the .so files in [...].sdk/usr/lib/swift. You can find the SDK itself by looking inside the JSON file you supplied to --destination. You can simply copy the libraries into the same directory as the executable, because the $ORIGIN entry in the RUNPATH will find them there.
Alternatively, some of the libraries support static linking instead by building with --static-swift-stdlib. If that covers all the libraries you need, then you won’t need to copy anything.
@SDGGiesbrecht
the sdk path is /Library/Developer/SDKs/amd64-5.1.1-RELEASE.sdk Inside the sdk, I see usr/lib/swift/libswiftSwiftOnoneSupport.dylib but not libswiftSwiftOnoneSupport.so. I am not familiar with the internals, but a quick google search suggets .dylib could be renamed to .so for this purpose?
(by the way, Installing swift on linux worked, and then running the executable worked)
(by the way, Installing swift on linux worked, and then running the executable worked)
Yes, by installing Swift, you provided those libraries along with a whole lot of unnecessary things.
The risk in that is that you provided them in global paths. Since you cannot have two versions of Swift installed in the same place, and Swift is not API‐stable on Linux, your binary will be version‐locked with Swift and unable to coexist on the same machine as another binary installed the same way but locked to a different version of Swift.
sdk path is /Library/Developer/SDKs/amd64-5.1.1-RELEASE.sdk Inside the sdk, I see usr/lib/swift/libswiftSwiftOnoneSupport.dylib
If the toolchain/SDK combination links an .so but provides a .dylib, then it wasn’t assembled correctly. Maybe whoever assembled it was lazy because he or she never expected anyone to build without --static-swift-stdlib.
Instead, you could pull the libraries out of the .tar of Swift that you would otherwise have installed (they would be at roughly the same relative path). Then you could bundle those with your executable instead of the broken ones from the cross‐compilation toolchain.
I am sorry, I gave the incorrect path. After cd'ing into the sdk, I did an on ls on /usr/lib/swift, instead of usr/lib/swift.
Inside the sdk/usr/lib there are gcc, llvm-6.0, sasl2, ssl, and x86_64-linux-gnu dirs, but no swift directory. However, I did find .so files in usr/lib/x86_64-linux-gnu
In any case, I am happy to tar the libraries and package the binary with it. It's a good enough solution. I am sure static binary is in the works at swift.
I have this working for a simple executable project. It seems that my dependency on SwiftNIO is the first place where this falls down for cross-compilation:
/Users/jeff/Projects/EmojiClubServer/.build/checkouts/swift-nio/Sources/NIOHTTP1/HTTPResponseCompressor.swift:15:8: error: could not build C module 'CNIOZlib'
import CNIOZlib
Full Build Log
<module-includes>:1:10: note: in file included from <module-includes>:1:
#include "/Users/jeff/Projects/EmojiClubServer/.build/checkouts/swift-nio/Sources/CNIOZlib/include/CNIOZlib.h"
^
/Users/jeff/Projects/EmojiClubServer/.build/checkouts/swift-nio/Sources/CNIOZlib/include/CNIOZlib.h:17:10: error: 'zlib.h' file not found
#include <zlib.h>
^
/Users/jeff/Projects/EmojiClubServer/.build/checkouts/swift-nio/Sources/NIOHTTP1/HTTPResponseCompressor.swift:15:8: error: could not build C module 'CNIOZlib'
import CNIOZlib
^
<module-includes>:1:10: note: in file included from <module-includes>:1:
#include "/Users/jeff/Projects/EmojiClubServer/.build/checkouts/swift-nio/Sources/CNIOZlib/include/CNIOZlib.h"
^
/Users/jeff/Projects/EmojiClubServer/.build/checkouts/swift-nio/Sources/CNIOZlib/include/CNIOZlib.h:17:10: error: 'zlib.h' file not found
#include <zlib.h>
^
/Users/jeff/Projects/EmojiClubServer/.build/checkouts/swift-nio/Sources/NIOHTTP1/HTTPResponseCompressor.swift:15:8: error: could not build C module 'CNIOZlib'
import CNIOZlib
^
<module-includes>:1:10: note: in file included from <module-includes>:1:
#include "/Users/jeff/Projects/EmojiClubServer/.build/checkouts/swift-nio/Sources/CNIOZlib/include/CNIOZlib.h"
^
/Users/jeff/Projects/EmojiClubServer/.build/checkouts/swift-nio/Sources/CNIOZlib/include/CNIOZlib.h:17:10: error: 'zlib.h' file not found
#include <zlib.h>
^
/Users/jeff/Projects/EmojiClubServer/.build/checkouts/swift-nio/Sources/NIOHTTP1/HTTPResponseCompressor.swift:15:8: error: could not build C module 'CNIOZlib'
import CNIOZlib
^
<module-includes>:1:10: note: in file included from <module-includes>:1:
#include "/Users/jeff/Projects/EmojiClubServer/.build/checkouts/swift-nio/Sources/CNIOZlib/include/CNIOZlib.h"
^
/Users/jeff/Projects/EmojiClubServer/.build/checkouts/swift-nio/Sources/CNIOZlib/include/CNIOZlib.h:17:10: error: 'zlib.h' file not found
#include <zlib.h>
^
/Users/jeff/Projects/EmojiClubServer/.build/checkouts/swift-nio/Sources/NIOHTTP1/HTTPResponseCompressor.swift:15:8: error: could not build C module 'CNIOZlib'
import CNIOZlib
^
<module-includes>:1:10: note: in file included from <module-includes>:1:
#include "/Users/jeff/Projects/EmojiClubServer/.build/checkouts/swift-nio/Sources/CNIOZlib/include/CNIOZlib.h"
^
/Users/jeff/Projects/EmojiClubServer/.build/checkouts/swift-nio/Sources/CNIOZlib/include/CNIOZlib.h:17:10: error: 'zlib.h' file not found
#include <zlib.h>
^
/Users/jeff/Projects/EmojiClubServer/.build/checkouts/swift-nio/Sources/NIOHTTP1/HTTPResponseCompressor.swift:15:8: error: could not build C module 'CNIOZlib'
import CNIOZlib
^
<module-includes>:1:10: note: in file included from <module-includes>:1:
#include "/Users/jeff/Projects/EmojiClubServer/.build/checkouts/swift-nio/Sources/CNIOZlib/include/CNIOZlib.h"
^
/Users/jeff/Projects/EmojiClubServer/.build/checkouts/swift-nio/Sources/CNIOZlib/include/CNIOZlib.h:17:10: error: 'zlib.h' file not found
#include <zlib.h>
^
/Users/jeff/Projects/EmojiClubServer/.build/checkouts/swift-nio/Sources/NIOHTTP1/HTTPResponseCompressor.swift:15:8: error: could not build C module 'CNIOZlib'
import CNIOZlib
^
<module-includes>:1:10: note: in file included from <module-includes>:1:
#include "/Users/jeff/Projects/EmojiClubServer/.build/checkouts/swift-nio/Sources/CNIOZlib/include/CNIOZlib.h"
^
/Users/jeff/Projects/EmojiClubServer/.build/checkouts/swift-nio/Sources/CNIOZlib/include/CNIOZlib.h:17:10: error: 'zlib.h' file not found
#include <zlib.h>
^
/Users/jeff/Projects/EmojiClubServer/.build/checkouts/swift-nio/Sources/NIOHTTP1/HTTPResponseCompressor.swift:15:8: error: could not build C module 'CNIOZlib'
import CNIOZlib
^
<module-includes>:1:10: note: in file included from <module-includes>:1:
#include "/Users/jeff/Projects/EmojiClubServer/.build/checkouts/swift-nio/Sources/CNIOZlib/include/CNIOZlib.h"
^
/Users/jeff/Projects/EmojiClubServer/.build/checkouts/swift-nio/Sources/CNIOZlib/include/CNIOZlib.h:17:10: error: 'zlib.h' file not found
#include <zlib.h>
^
/Users/jeff/Projects/EmojiClubServer/.build/checkouts/swift-nio/Sources/NIOHTTP1/HTTPResponseCompressor.swift:15:8: error: could not build C module 'CNIOZlib'
import CNIOZlib
^
<module-includes>:1:10: note: in file included from <module-includes>:1:
#include "/Users/jeff/Projects/EmojiClubServer/.build/checkouts/swift-nio/Sources/CNIOZlib/include/CNIOZlib.h"
^
/Users/jeff/Projects/EmojiClubServer/.build/checkouts/swift-nio/Sources/CNIOZlib/include/CNIOZlib.h:17:10: error: 'zlib.h' file not found
#include <zlib.h>
^
/Users/jeff/Projects/EmojiClubServer/.build/checkouts/swift-nio/Sources/NIOHTTP1/HTTPResponseCompressor.swift:15:8: error: could not build C module 'CNIOZlib'
import CNIOZlib
^
This may be as simple as finding a Linux version of zlib and making sure that that C flag is set, but I’m not sure where to set it.
I was able to get zlib imports working by adding zlib1g-dev to the list of packages that the script looks for. Updating as I go in case this is useful to anyone. The next part of building Vapor that fails is this:
I used the script in the swiftpm repository, modified to include zlib. Then I compiled my project with swift build --destination /path/to/destination.json. I’ll share the modification to the script as a PR in case it’s useful to anyone.
