https://llvm.org/bugs/show_bug.cgi?id=28395
Bug ID: 28395
Summary: Libc++ must guard against C++17 inline variable ABI
breaks.
Product: libc++
Version: unspecified
Hardware: PC
OS: Windows NT
Status: NEW
Severity: normal
Priority: P
Component: All Bugs
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected]
Classification: Unclassified
C++17 inline variables change the semantics surrounding how static data members
are defined. Previously static data members were required to be explicitly
defined once. In C++17 the compiler emits a potentially-discardable
definition in every TU where the data member is ODR-used. Even explicit
definitions of inline variables can be discarded.
This is problematic for Libc++ since it causes definitions previously provided
by libc++.dylib to disappear. This can cause ABI breakage if a C++17 dylib is
linked with a C++14 program.
The following symbols in libc++.dylib are affected (as of July 1st, 2016):
* std::chrono::steady_clock::is_steady
* std::chrono::system_clock::is_steady
I will introduce a workaround in libc++ itself until PR28394 is resolved.
(https://llvm.org/bugs/show_bug.cgi?id=28394)
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