[SR-14126] Regression: Cross-compile host to iPhoneOS stopped working

[swift-ci]

Previous ID	SR-14126
Radar	rdar://problem/73770091
Original Reporter	yoni (JIRA User)
Type	Bug
Status	Closed
Resolution	Done

Attachment: Download

Environment

macOS 11.1

Swift cloned from https://github.com/apple/swift

Main branch.

Built with Ninja.

Clang version 12.0.0 (clang-1200.0.32.28)

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug, BuildScript, CMake
Assignee	@CodaFi
Priority	Medium

md5: 57805d3b9702704ea008460f92552183

Issue Description:

Cross-compiling Swift for iOS (using cross-compile-hosts=iphoneos-arm64) has recently stopped working.

I suspect the issue comes from deprecating min-version in this recent commit.

Seems min-version parameter might still be required by clang (using latest version 12.0.0 (clang-1200.0.32.28)).

On the first target (cmark-iphoneos-arm64), clang emits:
clang: warning: argument unused during compilation: '-arch arm64' [-Wunused-command-line-argument]
ld: warning: ignoring file CMakeFiles/cmTC_00702.dir/testCCompiler.c.o, building for iOS-x86_64 but attempting to link with file built for unknown-unsupported file format ( 0x7F 0x45 0x4C 0x46 0x02 0x01 0x01 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 )
{{ ld: warning: ignoring file /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS14.3.sdk/usr/lib/libSystem.tbd, missing required architecture x86_64 in file /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS14.3.sdk/usr/lib/libSystem.tbd (4 slices)}}
{{ Undefined symbols for architecture x86_64:}}
{{ "_main", referenced from:}}
{{ implicit entry/start for main executable}}
{{ ld: symbol(s) not found for architecture x86_64}}

For reference, the build flags for CMakeCCompilerId.o in latest code is:
;;-Wno-unknown-warning-option;-Werror=unguarded-availability-new;-arch;arm64;-target;arm64-apple-iphoneos14.0;-fno-stack-protector

which produce a wrong file type of:
ELF 64-bit LSB relocatable, ARM aarch64, version 1 (SYSV), not stripped

And the build flags from before the commit, which works:
;;-Wno-unknown-warning-option;-Werror=unguarded-availability-new;-arch;arm64;;-miphoneos-version-min=14.0;-fno-stack-protector

And correctly produce a Mach-O 64-bit object arm64.

{{ }}

[swift-ci]

Comment by Jonathan Hemi (JIRA)

CodaFi (JIRA User) would really appreciate your eyes on this if you get a a chance.

[CodaFi]

Could you provide the link line being emitted by clang? If that doesn’t contain a suitable -platform_version it will fall back to the host’s platform which id what it seems to be doing here.

[swift-ci]

Comment by Jonathan Hemi (JIRA)

I think this is everything, also attached the entire folders since they're small.

– Check for working C compiler: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang
– Check for working C compiler: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang - broken
CMake Error at /usr/local/Cellar/cmake/3.19.3/share/cmake/Modules/CMakeTestCCompiler.cmake:66 (message):
{{ The C compiler}}

"/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang"

is not able to compile a simple test program.

It fails with the following output:

Change Dir: /Users/jonathan/try/sw/host-build/Ninja-Release/cmark-iphoneos-arm64/CMakeFiles/CMakeTmp

{{ Run Build Command(s):/usr/local/bin/ninja cmTC_51f01 && [1/2][ 50%][0.034s] Building C object CMakeFiles/cmTC_51f01.dir/testCCompiler.c.o}}
{{ [2/2][100%][0.093s] Linking C executable cmTC_51f01}}
{{ FAILED: cmTC_51f01 }}
{{ : && /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang -Wno-unknown-warning-option -Werror=unguarded-availability-new -arch arm64 -target arm64-apple-iphoneos14.0 -fno-stack-protector -arch arm64 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS14.3.sdk -Wl,-search_paths_first -Wl,-headerpad_max_install_names CMakeFiles/cmTC_51f01.dir/testCCompiler.c.o -o cmTC_51f01 && :}}
{{ clang: warning: argument unused during compilation: '-arch arm64' [-Wunused-command-line-argument]}}
{{ clang: warning: argument unused during compilation: '-arch arm64' [-Wunused-command-line-argument]}}
{{ ld: warning: ignoring file CMakeFiles/cmTC_51f01.dir/testCCompiler.c.o, building for iOS-x86_64 but attempting to link with file built for unknown-unsupported file format ( 0x7F 0x45 0x4C 0x46 0x02 0x01 0x01 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 )}}
{{ ld: warning: ignoring file /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS14.3.sdk/usr/lib/libSystem.tbd, missing required architecture x86_64 in file /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS14.3.sdk/usr/lib/libSystem.tbd (4 slices)}}
{{ Undefined symbols for architecture x86_64:}}
{{ "_main", referenced from:}}
{{ implicit entry/start for main executable}}
{{ ld: symbol(s) not found for architecture x86_64}}
{{ clang: error: linker command failed with exit code 1 (use -v to see invocation)}}
{{ clang: error: linker (via gcc) command failed with exit code 1 (use -v to see invocation)}}
{{ ninja: build stopped: subcommand failed.}}

{{ }}

CMake will not be able to correctly generate this project.
Call Stack (most recent call first):
{{ CMakeLists.txt:2 (project)}}

– Configuring incomplete, errors occurred!
See also "/Users/jonathan/try/sw/host-build/Ninja-Release/cmark-iphoneos-arm64/CMakeFiles/CMakeOutput.log".
See also "/Users/jonathan/try/sw/host-build/Ninja-Release/cmark-iphoneos-arm64/CMakeFiles/CMakeError.log".
ERROR: command terminated with a non-zero exit status 1, aborting

ERROR: command terminated with a non-zero exit status 1, aborting

[swift-ci]

Comment by Jonathan Hemi (JIRA)

But the host is macOS, isn't the ELF a weird outcome?

[CodaFi]

Perhaps the issue is the old-style triple. Try `arm64-apple-ios14.0`. You may need to reconfigure your build.

[swift-ci]

Comment by Jonathan Hemi (JIRA)

No luck. It will not create the output folders, failing with:

[/Users/jonathan/try/sw/swift/utils/build-script] NOTE: Using toolchain default
+ /usr/libexec/PlistBuddy -c 'Print :SupportedTargets:macosx:Archs' /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.1.sdk/SDKSettings.plist
+ mkdir -p /Users/jonathan/try/sw/host-build/Ninja-Release
ERROR: unknown target: arm64-apple-ios14.0
ERROR: command terminated with a non-zero exit status 1, aborting

The error is coming from here and the expected triple format is parsed here (seems iphoneos-arm64 is the only valid option).

[swift-ci]

Comment by Jonathan Hemi (JIRA)

I think I can distill it to the simplest clang invocation of a 'return 0' c program:

~ clang -arch arm64 -target arm64-apple-iphoneos14.0 ./hello.c
ld: warning: ignoring file /var/folders/7f/tdyh3rw96rq2nf0w95btmb4h0000gn/T/hello-515e59.o, building for macOS-x86_64 but attempting to link with file built for unknown-unsupported file format ( 0x7F 0x45 0x4C 0x46 0x02 0x01 0x01 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 )
Undefined symbols for architecture x86_64:
{{ "_main", referenced from:}}
{{ implicit entry/start for main executable}}
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
clang: error: linker (via gcc) command failed with exit code 1 (use -v to see invocation)

vs.

~ clang -arch arm64 -miphoneos-version-min=14.0 ./hello.c
clang: warning: using sysroot for 'MacOSX' but targeting 'iPhone' [-Wincompatible-sysroot]
[... more warnings because I don't pass correct SDKs]

Get a Mach-O 64-bit executable arm64

[typesanitizer]

@swift-ci create

[CodaFi]

Okay, it's definitely the old-style triple being passed to clang (not to build script). Check out the difference here

clang -Wno-unknown-warning-option -Werror=unguarded-availability-new -arch arm64 -target arm64-apple-ios14.0 -fno-stack-protector -v -c /Users/rwidmann/Downloads/cmark-iphoneos-arm64/CMakeFiles/3.19.3/CompilerIdC/CMakeCCompilerId.c -o /Users/rwidmann/Downloads/cmark-iphoneos-arm64/CMakeFiles/3.19.3/CompilerIdC/CMakeCCompilerId.o

objdump --headers /Users/rwidmann/Downloads/cmark-iphoneos-arm64/CMakeFiles/3.19.3/CompilerIdC/CMakeCCompilerId.o | head -n 2

/Users/rwidmann/Downloads/cmark-iphoneos-arm64/CMakeFiles/3.19.3/CompilerIdC/CMakeCCompilerId.o:    file format mach-o arm64

versus

clang -Wno-unknown-warning-option -Werror=unguarded-availability-new -arch arm64 -target arm64-apple-iphoneos14.0 -fno-stack-protector -v -c /Users/rwidmann/Downloads/cmark-iphoneos-arm64/CMakeFiles/3.19.3/CompilerIdC/CMakeCCompilerId.c -o /Users/rwidmann/Downloads/cmark-iphoneos-arm64/CMakeFiles/3.19.3/CompilerIdC/CMakeCCompilerId.o 

objdump --headers /Users/rwidmann/Downloads/cmark-iphoneos-arm64/CMakeFiles/3.19.3/CompilerIdC/CMakeCCompilerId.o | head -n 2

/Users/rwidmann/Downloads/cmark-iphoneos-arm64/CMakeFiles/3.19.3/CompilerIdC/CMakeCCompilerId.o:    file format elf64-littleaarch64

[CodaFi]

Please ensure you have this patch applied to your checkout f9be289b9e04b3d7650a6c093e624ff321cf399b, then remove your build directory and rerun the build.

[swift-ci]

Comment by Jonathan Hemi (JIRA)

Just saw the patch. Indeed this solves the issue.

Thanks so much!