Cross-compiling from aarch64 to x86_64, error: unknown target 'x86_64'

[deze333]

Using M4 macOS as a host. Followed the instructions and successfully built two Linux SDKs:

> swift sdk list
6.0.2-RELEASE_ubuntu_jammy_aarch64
6.0.2-RELEASE_ubuntu_jammy_x86_64

Next created an example project cross-compilation-test, just as described in the docs.

Compiling on Apple Silicon for Linux with same architecture works:

swift build --swift-sdk 6.0.2-RELEASE_ubuntu_jammy_aarch64

Compiling on Apple Silicon for Linux with Intel architecture fails:

swift build --swift-sdk 6.0.2-RELEASE_ubuntu_jammy_x86_64

Building for debugging...
error: unknown target 'x86_64'

[xtremekforever]

Curious...if you use the latest main to generate a 6.0.3 Swift SDK now, do you get the same error?

[deze333]

Same error unfortunately.

[MaxDesiatov]

Would you be able to provide the exact invocation you used to create the Swift SDK that you're getting an error with?

[deze333]

I have generated the SDK with

swift run swift-sdk-generator make-linux-sdk --target x86_64

Then

swift sdk install /Users/XYZ/swift-sdk-generator/Bundles/6.0.3-RELEASE_ubuntu_jammy_x86_64.artifactbundle

swift sdk list

Build a project

# created minimal project as per docs
cd ../cross-compilation-test 

swift build --swift-sdk 6.0.3-RELEASE_ubuntu_jammy_x86_64

# Error:
Building for debugging...
error: unknown target 'x86_64'

[euanh]

I have generated the SDK with

swift run swift-sdk-generator make-linux-sdk --target x86_64

Please try:

swift run swift-sdk-generator make-linux-sdk --target x86_64-unknown-linux-gnu

Note the full target triple of x86_64-unknown-linux-gnu in this command. With just x86_64 I see the same problem as you.

% swift run swift-sdk-generator make-linux-sdk --target x86_64 --sdk-name short-target
% swift sdk install Bundles/short-target.artifactbundle
# in test project
% swift build --swift-sdk short-target
Building for debugging...
error: unknown target 'x86_64'

% swift run swift-sdk-generator make-linux-sdk --target x86_64-unknown-linux-gnu --sdk-name long-target
% swift sdk install Bundles/short-target.artifactbundle
# in test project
% swift build --swift-sdk long-target                                                                                        
Building for debugging...
<unknown>:0: warning: libc not found for 'x86_64-unknown-linux-gnu'; C stdlib may be unavailable
<unknown>:0: warning: libc not found for 'x86_64-unknown-linux-gnu'; C stdlib may be unavailable
[8/8] Linking tmp
Build complete! (2.11s)

[xtremekforever]

Note the full target triple of x86_64-unknown-linux-gnu in this command. With just x86_64 I see the same problem as you.

This makes me wonder if we shouldn't put in a validation to make sure that the whole triple is provided to --target since if you don't it'll just use whatever you pass instead, which is invalid. We also have --target-arch to just specify the target architecture that defaults to *-unknown-linux-gnu, so maybe --target should enforce the whole triple.

[deze333]

The full triple SDK build almost works... until the error message about missing"swift-autolink-extract". I am on macOS.

swift run swift-sdk-generator make-linux-sdk --target x86_64-unknown-linux-gnu

# install SDK, then build project:

swift build --swift-sdk 6.0.3-RELEASE_ubuntu_jammy_x86_64 
Building for debugging...
<unknown>:0: warning: libc not found for 'x86_64-unknown-linux-gnu'; C stdlib may be unavailable
<unknown>:0: warning: libc not found for 'x86_64-unknown-linux-gnu'; C stdlib may be unavailable
error: unableToFind(tool: "swift-autolink-extract")
[7/8] Linking cross-compilation-test

[euanh]

The full triple SDK build almost works... until the error message about missing"swift-autolink-extract". I am on macOS.

Which version of macOS are you running, and which version of Xcode do you have installed?

[deze333]

Here's what I have (pretty much the latest to date):

macOS Sequia 15.3.2 (24D81)

Xcode 16.2

swift-driver version: 1.115.1 Apple Swift version 6.0.3 (swiftlang-6.0.3.1.10 clang-1600.0.30.1)
Target: arm64-apple-macosx15.0

What I have found is that the Xcode Swift toolchain isn't sufficient for cross-compilation as it's for Darwin only. One needs to download another 6.03 toolchain from swift.org

So I ended up having two toolchains for same 6.03 version. If I switch to the cross-compilation toolchain then the build succeeds.

It may be helpful to somebody struggling like myself.

[xtremekforever]

What I have found is that the Xcode Swift toolchain isn't sufficient for cross-compilation as it's for Darwin only. One needs to download another 6.03 toolchain from swift.org

So I ended up having two toolchains for same 6.03 version. If I switch to the cross-compilation toolchain then the build succeeds.

It may be helpful to somebody struggling like myself.

Seems like this is what most people are doing on macOS. There is the --host-toolchain param that can be added to include the open source toolchain in the Swift SDK:

swift run swift-sdk-generator make-linux-sdk --target x86_64-unknown-linux-gnu --host-toolchain

So then you don't have to switch between versions in Xcode. But, that's up to you on how you want to set things up.

[deze333]

Seems like this is what most people are doing on macOS. There is the --host-toolchain param that can be added to include the open source toolchain in the Swift SDK:

swift run swift-sdk-generator make-linux-sdk --target x86_64-unknown-linux-gnu --host-toolchain

So then you don't have to switch between versions in Xcode. But, that's up to you on how you want to set things up.

Yes, I can see that it now downloads the whole open source toolchain and indeed successfully compiles the project. But it also spits out LOTS of duplicate library warnings found between newly installed open source toolchain and Xcode toolchain:

> swift build --swift-sdk 6.0.3-RELEASE_ubuntu_jammy_x86_64

objc[59766]: Class _TtC19CompilerSwiftSyntax16BumpPtrAllocator is implemented in both /Users/XXX/Library/org.swift.swiftpm/swift-sdks/6.0.3-RELEASE_ubuntu_jammy_x86_64.artifactbundle/6.0.3-RELEASE_ubuntu_jammy_x86_64/x86_64-unknown-linux-gnu/swift.xctoolchain/usr/lib/swift/host/libSwiftSyntax.dylib (0x1193e5138) and /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/host/libSwiftSyntax.dylib (0x117d52138). One of the two will be used. Which one is undefined.

objc[59766]: Class _TtC19CompilerSwiftSyntax23SourceLocationConverter is implemented in both /Users/XXX/Library/org.swift.swiftpm/swift-sdks/6.0.3-RELEASE_ubuntu_jammy_x86_64.artifactbundle/6.0.3-RELEASE_ubuntu_jammy_x86_64/x86_64-unknown-linux-gnu/swift.xctoolchain/usr/lib/swift/host/libSwiftSyntax.dylib (0x1193e5350) and /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/host/libSwiftSyntax.dylib (0x117d52350). One of the two will be used. Which one is undefined.

# and so on...

Any tips on how to avoid this?

[xtremekforever]

I'm not sure there's a workaround for that, but it seems like undesired behavior to me. I also see that happening on my macOS when I include the host toolchain in the Swift SDK, but am using the open-source toolchain with Swiftly.

This does not happen on Linux hosts, so I think it's probably a bug or non-optimal behavior. @MaxDesiatov should we file a bug for this somewhere (maybe SwiftPM project) to start tracking a fix for it?