[llvm-shlib] Do not use version script when building with MinGW

[pirama]

Summary

The MinGW driver for lld does not support the --version-script option.
For GNU ld, it's a no-op since LLVM.dll exports all symbols.

[mstorsjo]

I'd suggest skipping the lld condition, the version script adds no value here.

For ELF, version scripts do two things, select what symbols to export using glob pattetns, and set symbol versions on them.

As COFF doesn't have symbol versions, all it does on mingw with GNU ld, is filtering symbols, to export *. So it adds no value there.

(I don't remember if cmake even knows the linker is lld in my mingw setups.)

[pirama]

In D63743#1556912, @mstorsjo wrote:

I'd suggest skipping the lld condition, the version script adds no value here.

For ELF, version scripts do two things, select what symbols to export using glob pattetns, and set symbol versions on them.

As COFF doesn't have symbol versions, all it does on mingw with GNU ld, is filtering symbols, to export *. So it adds no value there.

I thought so - that -version-script is not needed for Windows but wanted to leave it just in case GNU ld did something with it. I'll skip this option altogether for MinGW unless someone suggests otherwise.

(I don't remember if cmake even knows the linker is lld in my mingw setups.)

It does know - LINKER_IS_LLD_LINK is set at the top of llvm/cmake/modules/HandleLLVMOptions.cmake.

[pirama]

Skip version script for all MinGW builds, not just when using lld.

[mstorsjo]

LGTM

llvm/trunk/tools/llvm-shlib/CMakeLists.txt

if(("${CMAKE_SYSTEM_NAME}" STREQUAL "Linux") OR (MINGW) OR (HAIKU)
      OR ("${CMAKE_SYSTEM_NAME}" STREQUAL "DragonFly")
      OR ("${CMAKE_SYSTEM_NAME}" STREQUAL "SunOS")) # FIXME: It should be "GNU ld for elf"
     configure_file(
     ${CMAKE_CURRENT_SOURCE_DIR}/simple_version_script.map.in
     ${LLVM_LIBRARY_DIR}/tools/llvm-shlib/simple_version_script.map)
 
     # GNU ld doesn't resolve symbols in the version script.
     set(LIB_NAMES -Wl,--whole-archive ${LIB_NAMES} -Wl,--no-whole-archive)
-    if (NOT LLVM_LINKER_IS_SOLARISLD)
+    if (NOT LLVM_LINKER_IS_SOLARISLD AND NOT MINGW)
       # Solaris ld does not accept global: *; so there is no way to version *all* global symbols
       set(LIB_NAMES -Wl,--version-script,${LLVM_LIBRARY_DIR}/tools/llvm-shlib/simple_version_script.map ${LIB_NAMES})
     endif()
   elseif("${CMAKE_SYSTEM_NAME}" STREQUAL "Darwin")
     set(LIB_NAMES -Wl,-all_load ${LIB_NAMES})
   endif()
 
   target_link_libraries(LLVM PRIVATE ${LIB_NAMES})