Fix: Add -arch x86_64 to CXXFLAGS on macOS ARM64 to Resolve Linker Errors in Mixed C++ and D Testss

[gulugulubing]

Problem

On Apple Silicon, the default architecture for C++ compilers is ARM64,
which conflicts with DMD's x86_64 output. This causes linker errors when
building mixed C++ and D projects during make test.

Solution

This change adds -arch x86_64 to the CXXFLAGS to ensure the C++ compiler
generates x86_64 objects on macOS.

Testing

• Verified that the build succeeds on macOS with Apple Silicon.
• Confirmed that the generated objects are x86_64.
• All affected tests now pass without linker errors.

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Testing this PR locally

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[kinke]

#17035 shows that this isn't needed, on an arm64 macOS runner. The reason AFAIU being that both DMD and the testrunner are x86_64 executables, and in that case, the invoked universal cc/c++ binary defaults to the x86_64 version.

[gulugulubing]

#17035 shows that this isn't needed, on an arm64 macOS runner. The reason AFAIU being that both DMD and the testrunner are x86_64 executables, and in that case, the invoked universal cc/c++ binary defaults to the x86_64 version.

Thank you for your feedback! I understand the discussion in the referenced issue is about building and running DMD natively on ARM64 macOS, which is a different scenario from my PR.

My issue occurs during the testing phase after building, specifically when running make test. The problem is that the C++ compiler defaults to generating ARM64 code on Apple Silicon, while DMD generates x86_64 code. This causes linker errors when linking mixed C++ and D code. Here's an example of the error:

ld: warning: ignoring file '/dlang/dmd/compiler/test/test_results/runnable_cxx/d/test6716.cpp.o': found architecture 'arm64', required architecture 'x86_64'
Undefined symbols for architecture x86_64:
"_main", referenced from:

ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
Error: undefined reference to _main
perhaps a library needs to be added with the -L flag or pragma(lib, ...)
Error: linker exited with status 1

[kinke]

I understand the discussion in the referenced issue is about building and running DMD natively on ARM64 macOS, which is a different scenario from my PR.

Yeah the PR is a bit messy (still in draft) - but what's key is that it adds a macOS 14 job using latest DMD (and another one using LDC). That is a job that builds an x86_64 DMD (not a native arm64 one) on a M1 runner, and then runs all tests as x86_64, no arm64 involved anywhere. And that job works today, without any changes, especially no -arch x86_64 switches - the 1st commit alone passed that job (835d2b9).

Which make are you using? For CI there, we use brew install make and then the /opt/homebrew/opt/make/libexec/gnubin/make binary. Just in case there's an arch difference across CI and your box for that executable; it's the top-most process when running make test. Oh wait, just seen that CI doesn't run make test, but runs the tests manually:

dmd/ci/run.sh

Lines 131 to 132 in a4cbc08

	$build_path/dmd -g -i -Icompiler/test -release compiler/test/run.d -ofgenerated/run
	generated/run -j$N --environment MODEL=$MODEL HOST_DMD=$build_path/dmd "${args[@]}"

So I guess it's plausible that make gets in the way and causes these issues on your box. Maybe there's a way to put it into x86_64 mode? (I don't have Apple stuff.)

---

What we definitely don't want are hardcoded -arch x86_64 flags here in these test files. E.g., LDC supports arm64 too and runs these tests, on native M1 runners.

[gulugulubing]

I understand the discussion in the referenced issue is about building and running DMD natively on ARM64 macOS, which is a different scenario from my PR.

Yeah the PR is a bit messy (still in draft) - but what's key is that it adds a macOS 14 job using latest DMD (and another one using LDC). That is a job that builds an x86_64 DMD (not a native arm64 one) on a M1 runner, and then runs all tests as x86_64, no arm64 involved anywhere. And that job works today, without any changes, especially no -arch x86_64 switches - the 1st commit alone passed that job (835d2b9).

Which make are you using? For CI there, we use brew install make and then the /opt/homebrew/opt/make/libexec/gnubin/make binary. Just in case there's an arch difference across CI and your box for that executable; it's the top-most process when running make test. Oh wait, just seen that CI doesn't run make test, but runs the tests manually:

dmd/ci/run.sh

Lines 131 to 132 in a4cbc08

	$build_path/dmd -g -i -Icompiler/test -release compiler/test/run.d -ofgenerated/run
	generated/run -j$N --environment MODEL=$MODEL HOST_DMD=$build_path/dmd "${args[@]}"

So I guess it's plausible that make gets in the way and causes these issues on your box. Maybe there's a way to put it into x86_64 mode? (I don't have Apple stuff.)

What we definitely don't want are hardcoded -arch x86_64 flags here in these test files. E.g., LDC supports arm64 too and runs these tests, on native M1 runners.

My make version is :
GNU Make 4.4.1
Built for aarch64-apple-darwin23.4.0

As a newcomer to contributing, I'm still getting familiar with the D language build process. Modifying the complex scripts or Makefile to enforce arch -x86_64 feels a bit challenging for me at this stage. Therefore, I tried making the change directly in the test files instead. While I understand this approach may seem less elegant, it appeared to be simpler and more controllable for me as a beginner. I appreciate your understanding and guidance!

[kinke]

No worries, and thx for contributing! :)

You could add some implicit args after this line:

dmd/compiler/test/tools/d_do_test.d

Line 741 in a4cbc08

findTestParameter(envData, file, "CXXFLAGS", testArgs.cxxflags);

E.g.:

// DMD on macOS: force Apple clang to produce x86_64 code (on arm64 too), like DMD
version (DigitalMars) version (OSX)
    testArgs.cxxflags ~= " -arch x86_64";

Edit: Or append them after this:

dmd/compiler/test/tools/d_do_test.d

Lines 1108 to 1109 in a4cbc08

	if (cxxflags)
	command ~= " " ~ cxxflags;

[gulugulubing]

No worries, and thx for contributing! :)

You could add some implicit args after this line:

dmd/compiler/test/tools/d_do_test.d

Line 741 in a4cbc08

findTestParameter(envData, file, "CXXFLAGS", testArgs.cxxflags);

E.g.:

// DMD on macOS: force Apple clang to produce x86_64 code (on arm64 too), like DMD
version (DigitalMars) version (OSX)
    testArgs.cxxflags ~= " -arch x86_64";

Edit: Or append them after this:

dmd/compiler/test/tools/d_do_test.d

Lines 1108 to 1109 in a4cbc08

	if (cxxflags)
	command ~= " " ~ cxxflags;

Thank you! I tried modifying the d_do_test.d file by adding the -arch x86_64 flag in the two suggested locations, but the test process still fails with the same error.

[thewilsonator]

CI is green now, this good to go?

[kinke]

Have you read what I wrote? No hardcoded args in these test files.