Summary: | Dllexport for explicit template instantiation missing inline methods | ||
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Product: | gcc | Reporter: | Martin Storsjö <martin> |
Component: | c++ | Assignee: | Not yet assigned to anyone <unassigned> |
Status: | UNCONFIRMED --- | ||
Severity: | normal | CC: | aladjev.andrew, vittorio.romeo, webrown.cpp |
Priority: | P3 | Keywords: | link-failure |
Version: | 8.2.0 | ||
Target Milestone: | --- | ||
See Also: | https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99741 | ||
Host: | Target: | *-*-mingw* | |
Build: | Known to work: | ||
Known to fail: | Last reconfirmed: | ||
Attachments: | Sample code showing the issue |
FWIW, Clang (when operating in MinGW mode, where it tries to follow what GCC does) also had the same issue. There this issue was fixed by making dllexport export inline methods as well, for template instantiations: https://github.com/llvm-project/clang/commit/2061b0cab0002c264af632bf5e6ba5306c589c94 Bumped into this issue today. I confirm that it is still present on gcc version 12.2.0, on MSYS2. Any workaround that does not require exporting all symbols via '-Wl,--export-all-symbols'? |
Created attachment 45538 [details] Sample code showing the issue With dllexported explicit template instantiation, inline methods aren't exported, but callers still create undefined references to the inline methods, which fail due to the missing export. (This can be remedied by applying -Wl,--export-all-symbols to export all generated symbols, regardless of dllexport attributes.) Example: header.h: template <class T> struct C { void f(); void g() {} }; template <class T> void C<T>::f() {} extern template class #ifdef DLLEXPORT __declspec(dllexport) #elif defined(DLLIMPORT) __declspec(dllimport) #endif C<char>; lib.cpp: #define DLLEXPORT #include "header.h" template class C<char>; caller.cpp: #define DLLIMPORT #include "header.h" int main(int argc, char* argv[]) { C<char> a; a.g(); return 0; } Building of this fails in this way: $ make x86_64-w64-mingw32-g++ -c -o caller.o caller.cpp x86_64-w64-mingw32-g++ -c -o lib.o lib.cpp x86_64-w64-mingw32-g++ -shared -o lib.dll lib.o -Wl,--out-implib,liblib.dll.a x86_64-w64-mingw32-g++ -o caller.exe caller.o -L. -llib caller.o:caller.cpp:(.text+0x1c): undefined reference to `C<char>::g()' collect2: error: ld returned 1 exit status Makefile:5: recipe for target 'caller.exe' failed make: *** [caller.exe] Error 1 The instantiation definition in lib.cpp emitted both methods, but only export the non-inline method: $ x86_64-w64-mingw32-nm lib.o <snip> 0000000000000000 T _ZN1CIcE1fEv 0000000000000000 T _ZN1CIcE1gEv $ x86_64-w64-mingw32-objdump -s lib.o <snip> Contents of section .drectve: 0000 202d6578 706f7274 3a225f5a 4e314349 -export:"_ZN1CI 0010 63453166 45762200 cE1fEv". However, despite this, the caller creates an undefined reference to the inline method: $ x86_64-w64-mingw32-nm caller.o <snip> 0000000000000000 T main U _ZN1CIcE1gEv