@llvm/pr-subscribers-clang

Author: None (jeremyd2019)

diff --git a/clang/include/clang-c/Platform.h b/clang/include/clang-c/Platform.h
index 67c1fff8ff783..8d341ddd6f8eb 100644
--- a/clang/include/clang-c/Platform.h
+++ b/clang/include/clang-c/Platform.h
@@ -22,7 +22,7 @@ LLVM_CLANG_C_EXTERN_C_BEGIN
 #ifndef CINDEX_NO_EXPORTS
   #define CINDEX_EXPORTS
 #endif
-#ifdef _WIN32
+#if defined(_WIN32) || defined(__CYGWIN__)
   #ifdef CINDEX_EXPORTS
     #ifdef _CINDEX_LIB_
       #define CINDEX_LINKAGE __declspec(dllexport)
diff --git a/clang/tools/libclang/CMakeLists.txt b/clang/tools/libclang/CMakeLists.txt
index 37a939ffcada7..454dfead0bcf5 100644
--- a/clang/tools/libclang/CMakeLists.txt
+++ b/clang/tools/libclang/CMakeLists.txt
@@ -158,7 +158,7 @@ if(ENABLE_STATIC)
 endif()
 
 if(ENABLE_SHARED)
-  if(WIN32)
+  if(WIN32 OR CYGWIN)
     set_target_properties(libclang
       PROPERTIES
       VERSION ${LIBCLANG_LIBRARY_VERSION}

⚠️ C/C++ code formatter, clang-format found issues in your code. ⚠️

git-clang-format --diff HEAD~1 HEAD --extensions h -- clang/include/clang-c/Platform.h

diff --git a/clang/include/clang-c/Platform.h b/clang/include/clang-c/Platform.h
index 8d341ddd6..1c28ccf81 100644
--- a/clang/include/clang-c/Platform.h
+++ b/clang/include/clang-c/Platform.h
@@ -23,13 +23,13 @@ LLVM_CLANG_C_EXTERN_C_BEGIN
   #define CINDEX_EXPORTS
 #endif
 #if defined(_WIN32) || defined(__CYGWIN__)
-  #ifdef CINDEX_EXPORTS
-    #ifdef _CINDEX_LIB_
-      #define CINDEX_LINKAGE __declspec(dllexport)
-    #else
-      #define CINDEX_LINKAGE __declspec(dllimport)
-    #endif
-  #endif
+#ifdef CINDEX_EXPORTS
+#ifdef _CINDEX_LIB_
+#define CINDEX_LINKAGE __declspec(dllexport)
+#else
+#define CINDEX_LINKAGE __declspec(dllimport)
+#endif
+#endif
 #elif defined(CINDEX_EXPORTS) && defined(__GNUC__)
   #define CINDEX_LINKAGE __attribute__((visibility("default")))
 #endif

I think it works when you build with Clang rather than GCC. Clang will not export symbols with hidden visibility.

But people build mingw clang with gcc, right? They presumably don't set LLVM_ENABLE_PIC=OFF. It seems like having explicit dllexport annotations as libclang does should turn off auto-export. I didn't see --export-all-symbols in the command line anyway.

But people build mingw clang with gcc, right?

Dunno.

It seems like having explicit dllexport annotations as libclang does should turn off auto-export. I didn't see --export-all-symbols in the command line anyway.

Yes, linker exports all the symbols by default, but explicit export disable that.

Offhand, I don't quite know here. Which configurations is this about? For mingw, the only cases I'm familiar with is building with LLVM_LINK_LLVM_DYLIB=ON, which iirc implicitly enables a corresponding one for Clang too. Not sure which of the local variables here that maps to without trying and tracing it.

Building that kind of dylib used to work with GCC, but these days it probably hits the limit on the number of exported symbols (initially in libLLVM-*.dll), unless you reduce the number of enabled targets a lot.

-DLLVM_BUILD_LLVM_DYLIB=OFF -DLLVM_LINK_LLVM_DYLIB=OFF -DLIBCLANG_BUILD_STATIC=ON

Now we know that adding -DLLVM_ENABLE_PIC=OFF will turn off building libclang.dll, but otherwise it will be built regardless.

Surprisingly, it looks like Cygwin (@tyan0) is working around the export limit on gcc by setting -DCMAKE_SHARED_LINKER_FLAGS=-fvisibility=hidden. I was surprised that worked on gcc - maybe it can be generalized here instead of fighting to build only static with gcc to then use that clang to build dynamic libraries?

Surprisingly, it looks like Cygwin (@tyan0) is working around the export limit on gcc by setting -DCMAKE_SHARED_LINKER_FLAGS=-fvisibility=hidden.

This was my misunderstanding. Building successfully was due to -DLLVM_TARGETS_TO_BUILD=X86 which restrict target architecture only to x86. -fvisibility=hidden does not seem to take effect.

I wonder why your msys2 build scripts does not fail to build even with -DLLVM_TARGETS_TO_BUILD="AArch64;ARM;X86" and gcc/g++.

Surprisingly, it looks like Cygwin (@tyan0) is working around the export limit on gcc by setting -DCMAKE_SHARED_LINKER_FLAGS=-fvisibility=hidden.

This was my misunderstanding. Building successfully was due to -DLLVM_TARGETS_TO_BUILD=X86 which restrict target architecture only to x86. -fvisibility=hidden does not seem to take effect.

Thanks for clarifying this!

Indeed, -fvisibility=hidden (or __attribute__((visibility("hidden"))) or -fvisibility-inlines-hidden etc) only have an effect with Clang, but the embedded attributes for omitting symbols from autoexport that it produces are honored by both ld.bfd and LLD.