Buildroot patch:

https://gist.github.com/colemancda/e2d7923b51697edec61c0004dfece150

Buildroot config for Armv7:

https://gist.github.com/colemancda/9d8a9a6dcef9f6ae500be5ec31cb1f7c

Just change SWIFT_VERSION = 5.5.3 in Swift.mk for SWIFT_VERSION = 5.6 and it will successfully build a Armv7 binary, however this binary crashes both in QEMU and on real hardware.

I am unable to reproduce with my Android armv7 SDK when cross-compiling with a prebuilt Swift 5.6 for linux x86_64 by using a modified version of the command from the compiler's Android doc:

./swift-5.6-RELEASE-ubuntu20.04/usr/bin/swiftc -tools-directory /home/butta/android-ndk-r23b/toolchains/llvm/prebuilt/linux-x86_64/bin/ -target armv7-unknown-linux-androideabi24 -sdk android-ndk-r23b/toolchains/llvm/prebuilt/linux-x86_64/sysroot/ -resource-dir swift-5.6-android-armv7-24-sdk/usr/lib/swift swift/test/Interpreter/hello_toplevel.swift

The async hello world swift/test/Interpreter/async.swift also works, if I add the -parse-as-library flag when cross-compiling. I can also cross-compile Swift packages for Android armv7 using SPM and run the tests for packages like swift-argument-parser, swift-crypto, and swift-nio by using the instructions in my SDK doc.

This suggests the problem is not with armv7 but with the particular way you are building, which may have worked with Swift 5.5 but not 5.6.

@buttaface I was able to cross compile the Swift stdlib for Debian 11 (armhf), so this must be an issue with the Swift Buildroot package.

https://github.com/colemancda/swift-armv7

@buttaface After some digging and diffing the cmake cache files, I discovered that the culprit was the default Swift flags.

//Swift Compiler Flags during all build types.
CMAKE_Swift_FLAGS:STRING=
CMAKE_Swift_FLAGS_DEBUG:STRING=-g
CMAKE_Swift_FLAGS_MINSIZEREL:STRING=-Osize
CMAKE_Swift_FLAGS_RELEASE:STRING=-O
CMAKE_Swift_FLAGS_RELWITHDEBINFO:STRING=-O -g

And was able to get a valid binary with the following flags
-DCMAKE_Swift_FLAGS="" \
-DCMAKE_Swift_FLAGS_RELEASE="" \
-DCMAKE_Swift_FLAGS_RELWITHDEBINFO="" \

Fixed Buildroot patch https://gist.github.com/colemancda/e2d7923b51697edec61c0004dfece150