The point of the extern template was to prevent that operator from being
defined in any other object files. The extern template wasn't taking effect
because of its placement in the file, but I fixed that in r309474. Does your
issue get resolved with that second change in place?
From: <ahatan...@apple.com> on behalf of Akira Hatanaka <ahatan...@apple.com>
Date: Tuesday, August 22, 2017 at 6:21 PM
To: Shoaib Meenai <smee...@fb.com>
Cc: "cfe-commits@lists.llvm.org" <cfe-commits@lists.llvm.org>
Subject: Re: [libcxx] r307966 - [libc++] Mark string operator+ _LIBCPP_FUNC_VIS
This change makes it impossible to change the visibility of operator+ with
-fvisibility=hidden, which is not desirable on Darwin.
For example:
$ cat test.cpp
#include <string>
using namespace std;
string foo1(string s) {
return "abc" + s;
}
$ clang++ test.cpp -fvisibility=hidden -c; nm -m -a test.o | grep
__ZNSt3__1plIcNS_11char_traitsIcEENS_9allocatorIcEEEENS_12basic_stringIT_T0_T1_EEPKS6_RKS9_
0000000000000030 (__TEXT,__text) weak external
__ZNSt3__1plIcNS_11char_traitsIcEENS_9allocatorIcEEEENS_12basic_stringIT_T0_T1_EEPKS6_RKS9_
The symbol used to be “weak private external”, but it is “weak external” now.
On Jul 13, 2017, at 2:35 PM, Shoaib Meenai via cfe-commits
<cfe-commits@lists.llvm.org<mailto:cfe-commits@lists.llvm.org>> wrote:
Author: smeenai
Date: Thu Jul 13 14:35:52 2017
New Revision: 307966
URL:
http://llvm.org/viewvc/llvm-project?rev=307966&view=rev<https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject-3Frev-3D307966-26view-3Drev&d=DwMFaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=fSgXogPdeBdhqIn59AresTrI4a5SvxnrlrH4EXmRKw4&s=uHFcqiGZetyK3t7-YYvkubjoCERPfi_DGNp3ZwQn-_g&e=>
Log:
[libc++] Mark string operator+ _LIBCPP_FUNC_VIS
It has an extern template instantiation declaration in the headers and a
corresponding instantiation definition in the library, so we must mark
it with _LIBCPP_FUNC_VIS to make it available outside the library.
This doesn't cause any ABI changes as-is since we don't build libc++
with hidden visibility (so the function is exported anyway). It's needed
for building libc++ with hidden visibility, however.
Clarify the Windows behavior for extern function templates while I'm
here, since this exercises that behavior.
Modified:
libcxx/trunk/docs/DesignDocs/VisibilityMacros.rst
libcxx/trunk/include/string
Modified: libcxx/trunk/docs/DesignDocs/VisibilityMacros.rst
URL:
http://llvm.org/viewvc/llvm-project/libcxx/trunk/docs/DesignDocs/VisibilityMacros.rst?rev=307966&r1=307965&r2=307966&view=diff<https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject_libcxx_trunk_docs_DesignDocs_VisibilityMacros.rst-3Frev-3D307966-26r1-3D307965-26r2-3D307966-26view-3Ddiff&d=DwMFaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=fSgXogPdeBdhqIn59AresTrI4a5SvxnrlrH4EXmRKw4&s=g6z9tFqcc6oS9s7ahnZSfMluaIqZ7wif_ft33mP7H18&e=>
==============================================================================
--- libcxx/trunk/docs/DesignDocs/VisibilityMacros.rst (original)
+++ libcxx/trunk/docs/DesignDocs/VisibilityMacros.rst Thu Jul 13 14:35:52 2017
@@ -98,7 +98,8 @@ Visibility Macros
explicit instantiations themselves are marked as exported. Note that this
applies *only* to extern *class* templates. Extern *function* templates obey
regular import/export semantics, and applying `dllexport` directly to the
- extern template declaration is the correct thing to do for them.
+ extern template declaration (i.e. using `_LIBCPP_FUNC_VIS`) is the correct
+ thing to do for them.
**_LIBCPP_CLASS_TEMPLATE_INSTANTIATION_VIS**
Mark the member functions, typeinfo, and vtable of an explicit instantiation
Modified: libcxx/trunk/include/string
URL:
http://llvm.org/viewvc/llvm-project/libcxx/trunk/include/string?rev=307966&r1=307965&r2=307966&view=diff<https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject_libcxx_trunk_include_string-3Frev-3D307966-26r1-3D307965-26r2-3D307966-26view-3Ddiff&d=DwMFaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=fSgXogPdeBdhqIn59AresTrI4a5SvxnrlrH4EXmRKw4&s=eoxEd6j-lxbIB3Nhf0bJFjtVvnXJq2lKJpLY_lTM8aY&e=>
==============================================================================
--- libcxx/trunk/include/string (original)
+++ libcxx/trunk/include/string Thu Jul 13 14:35:52 2017
@@ -4006,7 +4006,7 @@ basic_string<_CharT, _Traits, _Allocator
_LIBCPP_EXTERN_TEMPLATE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS
basic_string<char>)
_LIBCPP_EXTERN_TEMPLATE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS
basic_string<wchar_t>)
-_LIBCPP_EXTERN_TEMPLATE(string operator+<char, char_traits<char>,
allocator<char> >(char const*, string const&))
+_LIBCPP_EXTERN_TEMPLATE(_LIBCPP_FUNC_VIS string operator+<char,
char_traits<char>, allocator<char> >(char const*, string const&))
#if _LIBCPP_STD_VER > 11
// Literal suffixes for basic_string [basic.string.literals]
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