zahiraam added a comment. In D117569#3259255 <https://reviews.llvm.org/D117569#3259255>, @majnemer wrote:
> In D117569#3258307 <https://reviews.llvm.org/D117569#3258307>, @zahiraam > wrote: > >> In D117569#3257121 <https://reviews.llvm.org/D117569#3257121>, @majnemer >> wrote: >> >>> I have a question regarding how this work with respect to the dllimport >>> semantics known by the linker. >>> IIUC, we will now allow a program like: >>> >>> extern int __declspec(dllimport) dll_import_int; >>> constexpr int& dll_import_constexpr_ref = dll_import_int; >>> int& get() { >>> return dll_import_constexpr_ref; >>> } >>> >>> Here, `get` will load `dll_import_constexpr_ref`. However, what will >>> `dll_import_constexpr_ref` hold? It ought to hold the contents of >>> `__imp_?dll_import_int@@3HA`. However, we can't dereference >>> `__imp_?dll_import_int@@3HA` to get to its contents. >> >> @majnemer Thanks for the review. >> >> This test case doesn't link with MSVC. It will generate this error: >> Microsoft (R) Incremental Linker Version 14.29.30133.0 >> Copyright (C) Microsoft Corporation. All rights reserved. >> >> /out:test1.exe >> test1.obj >> test1.obj : error LNK2001: unresolved external symbol "int dll_import_int" >> (?dll_import_int@@3HA) >> test1.exe : fatal error LNK1120: 1 unresolved externals >> >> The symbols generated with MSVC are: >> 07 00000000 UNDEF notype External | ?dll_import_int@@3HA (int >> dll_import_int) >> 015 00000000 SECT6 notype Static | >> ?dll_import_constexpr_ref@@3AEAHEA (int & dll_import_constexpr_ref) >> >> Without this patch this test case errors. With this patch clang will >> generate these symbols: >> >> 010 00000000 UNDEF notype External | __imp_?dll_import_int@@3HA >> (__declspec(dllimport) int dll_import_int) >> 012 00000000 SECT5 notype External | >> ?dll_import_constexpr_ref@@3AEAHEA (int & dll_import_constexpr_ref) >> 013 00000000 UNDEF notype External | ?dll_import_int@@3HA (int >> dll_import_int) >> >> and will error at link time with this error: >> test1-f1f63b.o : error LNK2019: unresolved external symbol >> "__declspec(dllimport) int dll_import_int" (__imp_?dll_import_int@@3HA) >> referenced in function "int & __cdecl get(void)" (?get@@YAAEAHXZ) >> test1-f1f63b.o : error LNK2001: unresolved external symbol "int >> dll_import_int" (?dll_import_int@@3HA) >> a.exe : fatal error LNK1120: 2 unresolved externals >> >> I think that's the behavior expected, right? > > My interpretation is that MSVC has a bug: it is forming a reference to > `?dll_import_int@@3HA` and not `__imp_?dll_import_int@@3HA`. Could you run a > more complete experiment where you have a dll which exports the symbol and > you try to import it? This is what I did (before the complete experiment). For this test case: int& get() { extern int __declspec(dllimport) dll_import_int; constexpr int& dll_import_constexpr_ref = dll_import_int; return dll_import_constexpr_ref; } int main() { get(); return 0; } This is generating this symbol (with imp): ksh-3.2$ dumpbin /symbols test2.obj | grep dll 015 00000000 UNDEF notype External | **__imp**_?dll_import_int@@3HA (__declspec(dllimport) int dll_import_int) ksh-3.2$ With clang (with this patch) it is generating the same symbol: ksh-3.2$ dumpbin /symbols test2.o | grep dll 00E 00000000 UNDEF notype External | __imp_?dll_import_int@@3HA (__declspec(dllimport) int dll_import_int) ksh-3.2$ For this test case: extern int __declspec(dllexport) dll_export_int; constexpr int& dll_export_constexpr_ref = dll_export_int; int& get() { extern int __declspec(dllimport) dll_import_int; constexpr int& dll_import_constexpr_ref = dll_import_int; return dll_export_constexpr_ref; } int main() { get(); return 0; } MSVC is generating these symbols: ksh-3.2$ dumpbin /symbols test3.obj | grep dll 007 00000000 UNDEF notype External | ?dll_export_int@@3HA (int dll_export_int) 018 00000000 SECT6 notype Static | ?dll_export_constexpr_ref@@3AEAHEA (int & dll_export_constexpr_ref) 019 00000000 UNDEF notype External | __imp_?dll_import_int@@3HA (__declspec(dllimport) int dll_import_int) ksh-3.2$ clang (with this patch) is generating an error: test3.cpp:2:16: error: constexpr variable 'dll_export_constexpr_ref' must be initialized by a constant expression constexpr int& dll_export_constexpr_ref = dll_export_int; ^ ~~~~~~~~~~~~~~ 1 error generated. Your thoughts? CHANGES SINCE LAST ACTION https://reviews.llvm.org/D117569/new/ https://reviews.llvm.org/D117569 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
