On 19/07/18 16:58 -0700, Fāng-ruì Sòng via libstdc++ wrote:
clang (including trunk and many older versions) incorrectly marks static local
variables (__tag) hidden when -fvisibility-inlines-hidden is used.
% cat b.cc
#include <memory>
std::shared_ptr<int> foo(int x) {
return std::make_shared<int>(x);
}
% g++-8 -fvisibility-inlines-hidden -fno-rtti -c b.cc
% readelf -s b.o | grep _S_ti
163: 0000000000000000 1 OBJECT UNIQUE DEFAULT 67
_ZZNSt19_Sp_make_shared_tag5_S_tiEvE5__tag
164: 0000000000000000 8 FUNC WEAK HIDDEN 68
_ZNSt19_Sp_make_shared_tag5_S_tiEv
% ~/Dev/llvm/static-release/bin/clang++ -fvisibility-inlines-hidden -fno-rtti
-c b.cc
% readelf -s b.o | grep _S_ti
129: 0000000000000000 16 FUNC WEAK HIDDEN 34
_ZNSt19_Sp_make_shared_tag5_S_tiEv
155: 0000000000000000 1 OBJECT WEAK HIDDEN 202
_ZZNSt19_Sp_make_shared_tag5_S_tiEvE5__tag
This can lead to multiple instances of __tag when shares objects are used.
The function
virtual void* std::_Sp_counted_ptr_inplace::_M_get_deleter(const
std::type_info& __ti) noexcept
may return nullptr and causes std::make_shared<T>() to return nullptr
(-fvisibility-inlines-hidden -fno-rtti).
After applying this patch (tagging _S_ti() with default visibility to override
-fvisibility-inlines-hidden)
% readelf -s b.o | grep _S_ti
129: 0000000000000000 16 FUNC WEAK DEFAULT 34
_ZNSt19_Sp_make_shared_tag5_S_tiEv
155: 0000000000000000 1 OBJECT WEAK DEFAULT 202
_ZZNSt19_Sp_make_shared_tag5_S_tiEvE5__tag
This issue caused 10+ check-all tests of a -DUSE_SHARED_LLVM=On build of llvm
(compiled with clang trunk) to SIGSEGV (because std::make_shared returned
nullptr) and this patch fixes it.
* include/bits/shared_ptr_base.h (_S_ti): Use
_GLIBCXX_VISIBILITY(default)
Thanks, I've tested this and committed it to trunk.
I think we want this on gcc-8-branch too, but it's too late for the
8.2 release now.
--
宋方睿
From 6da8cec298766ce043d9c6dcda7b87142228dafb Mon Sep 17 00:00:00 2001
From: Fangrui Song <mask...@google.com>
Date: Thu, 19 Jul 2018 16:40:26 -0700
Subject: [PATCH 1/1] Explicitly mark _S_ti() as default visibility to work
around clang -fvisibility-inlines-hidden bug
clang (including trunk and many older versions) incorrectly marks static
local variables (__tag) hidden when -fvisibility-inlines-hidden is used.
This can lead to multiple instances of __tag when shares objects are used.
* include/bits/shared_ptr_base.h (_S_ti): Use
_GLIBCXX_VISIBILITY(default)
---
libstdc++-v3/include/bits/shared_ptr_base.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/libstdc++-v3/include/bits/shared_ptr_base.h
b/libstdc++-v3/include/bits/shared_ptr_base.h
index f3994da158f..870aeb9bfda 100644
--- a/libstdc++-v3/include/bits/shared_ptr_base.h
+++ b/libstdc++-v3/include/bits/shared_ptr_base.h
@@ -508,7 +508,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
friend class _Sp_counted_ptr_inplace;
static const type_info&
- _S_ti() noexcept
+ _S_ti() noexcept _GLIBCXX_VISIBILITY(default)
{
alignas(type_info) static constexpr _Sp_make_shared_tag __tag;
return reinterpret_cast<const type_info&>(__tag);
--
2.18.0
