undefined symbol: _DllMainCRTStartup when I use zig build-lib --dynamic to generate dynamic library on windows

[waruqi]

example project: https://github.com/xmake-io/xmake/tree/master/tests/projects/zig/shared_library

We can download xmake-latest.win64.exe install package to install xmake (dev version) from https://github.com/xmake-io/xmake/actions/runs/355512412

Then test this problem. (zig 0.7.0)

$ xmake f --zc=y:\zig\zig.exe
$ xmake -rv
[ 37%]: compiling.release src\main.zig
y:\zig\zig.exe build-obj -target x86_64-windows-msvc -O ReleaseFast -femit-bin=build\.objs\test\windows\x64\release\src\main.zig.obj src\main.zig
[ 50%]: compiling.release src\test.zig
y:\zig\zig.exe build-obj -target x86_64-windows-msvc -fPIC -O ReleaseFast -femit-bin=build\.objs\testlib\windows\x64\release\src\test.zig.obj src\test.zig
[ 62%]: linking.release testlib.dll
y:\zig\zig.exe build-lib -dynamic -fPIC -target x86_64-windows-msvc --strip -femit-bin=build\windows\x64\release\testlib.dll build\.objs\testlib\windows\x64\release\src\test.zig.obj
error: lld: error: <root>: undefined symbol: _DllMainCRTStartup
error: LLDReportedFailure

[alexnask]

This is quite tricky to solve.
One solution could be to add an empty module to the compilation when targetting a windows shared library with no zig file in the inputs.
This way, the start.zig code with generate and export the _DllMainCRTStartup symbol, however we don't know that the symbol is necessarily missing from the object files so start.zig would have to be modified to export it with weak linkage.
Maybe I'm missing some simpler solution, I will look into clang and LLD to see how they handle the same issue with -nostdlib.

[andrewrk]

This is another example where it would work if you gave build-lib source files instead of objects. This is an enhancement issue to support creating a special kind of object.

[waruqi]

This is another example where it would work if you gave build-lib source files instead of objects. This is an enhancement issue to support creating a special kind of object.

If I don’t pass the zig source files, can I just set additional linker flags to solve this problem?