[Bug](build): missing '-shared' flag causes 'undefined symbol: main' linker error when cross-compiling

[kengoon]

OS: MacOS 26.6 (M chip)
Python: 3.14
Kivy: 3.0 (master)

when p4a starts building kivy 3.0 it fails with this error:

clang++: warning: argument unused during compilation: '-bundle' [-Wunused-command-line-argument]
clang++: warning: argument unused during compilation: '-undefined dynamic_lookup' [-Wunused-command-line-argument]
ld.lld: error: undefined symbol: main
>>> referenced by crtbegin.c
>>>               /Users/kengoon/.buildozer/android/platform/android-ndk-r28c/toolchains/llvm/prebuilt/darwin-x86_64/bin/../sysroot/usr/lib/aarch64-linux-android/24/crtbegin_dynamic.o:(_start_main)
>>> referenced by crtbegin.c
>>>               /Users/kengoon/.buildozer/android/platform/android-ndk-r28c/toolchains/llvm/prebuilt/darwin-x86_64/bin/../sysroot/usr/lib/aarch64-linux-android/24/crtbegin_dynamic.o:(_start_main)
clang++: error: linker command failed with exit code 1 (use -v to see invocation)
 error: command '/opt/homebrew/bin/ccache' failed with exit code 1

but when I add " -shared" to LDFLAGS (this code below) it works fine:

python-for-android/pythonforandroid/recipes/kivy/__init__.py

Lines 59 to 64 in d156b3d

	# Taken from CythonRecipe
	env['LDFLAGS'] = env['LDFLAGS'] + ' -L{} '.format(
	self.ctx.get_libs_dir(arch.arch) +
	' -L{} '.format(self.ctx.libs_dir) +
	' -L{}'.format(join(self.ctx.bootstrap.build_dir, 'obj', 'local',
	arch.arch)))

I wanted to make a PR but I'm new on building with mac and I don't know whether adding -shared will break linux platform (not free to test on linux atm)

[T-Dynamos]

It's a general problem with cross compiling for Android from Mac.

Build system assumes we are building for mac and injects mac related flags. This works fine on linux as Android is effectively a linux.

[AndreMiras]

Thanks for reporting.
I think the root cause is that p4a never sets LDCXXSHARED, only LDSHARED.
You can see it on your machine:

python -c "import sysconfig; print(sysconfig.get_config_var('LDCXXSHARED'))"

On macOS that prints roughly clang++ -bundle -undefined dynamic_lookup, on
Linux g++ -pthread -shared ....

So on macOS the link becomes NDK clang++ -bundle -undefined dynamic_lookup ...
On Linux -shared survives, which is why the platform difference exists. That also answers your question: adding -shared to LDFLAGS won't break Linux, it's just a duplicate flag there.
But it fixes only the kivy recipe, and LDFLAGS also feeds autoconf-style link tests in other recipes.

A more targeted fix could be in in Arch.get_env():

env['LDSHARED'] = env['CC'] + ' ' + ' '.join(self.common_ldshared)
env['LDCXXSHARED'] = env['CXX'] + ' ' + ' '.join(self.common_ldshared)

and the matching line in the kivy recipe next to the existing LDSHARED
override:

env['LDCXXSHARED'] = env['CXX'] + ' -shared'

This is host-independent, so it should be a no-op on Linux CI while fixing macOS, and it covers every recipe with C++ extensions rather than just kivy.

I'll open a PR to address
Edit: #3371