[cfe-dev] [libc++] r160604 appears to have broken libc++ on linux

[Andrew C. Morrow]

I have a mostly working clang toolchain on Linux using libc++abi and
libc++. But today I pulled the latest updates to libc++ and rebuilt
it, and now any attempt to construct a std::stringstream fails.

#include <sstream>

int main(int argc, char* argv[]) {
    std::stringstream ss;
    return EXIT_SUCCESS;
}

This dies with an unhandled std::bad_cast exception:

terminating with uncaught exception of type std::bad_cast: std::bad_cast

Program received signal SIGABRT, Aborted.
0x00007ffff75f0475 in *__GI_raise (sig=<optimized out>) at
../nptl/sysdeps/unix/sysv/linux/raise.c:64
64	../nptl/sysdeps/unix/sysv/linux/raise.c: No such file or directory.
(gdb) where
#0  0x00007ffff75f0475 in *__GI_raise (sig=<optimized out>) at
../nptl/sysdeps/unix/sysv/linux/raise.c:64
#1  0x00007ffff75f36f0 in *__GI_abort () at abort.c:92
#2  0x00007ffff7fcd457 in abort_message (format=<optimized out>) at
../../../src/libcxxabi/src/abort_message.cpp:47
#3  0x00007ffff7fcd6c2 in default_handler (cause=0x7ffff7fe3ba3
"uncaught") at ../../../src/libcxxabi/src/cxa_default_handlers.cpp:61
#4  0x00007ffff7fcd54d in default_terminate_handler () at
../../../src/libcxxabi/src/cxa_default_handlers.cpp:81
#5  0x00007ffff7fe0676 in std::__terminate (func=0xeed9) at
../../../src/libcxxabi/src/cxa_handlers.cpp:67
#6  0x00007ffff7fdfce6 in failed_throw (exception_header=<optimized
out>) at ../../../src/libcxxabi/src/cxa_exception.cpp:147
#7  __cxa_throw (thrown_object=0x406090, tinfo=<optimized out>,
dest=<optimized out>) at
../../../src/libcxxabi/src/cxa_exception.cpp:242
#8  0x00007ffff7e8f857 in std::__1::locale::__imp::use_facet
(this=0x7ffff7faba70, id=28) at
/home/acm/Documents/Develop/externals/clang-toolchain/src/libcxx/src/locale.cpp:388
#9  0x00007ffff7e90633 in std::__1::locale::use_facet
(this=0x7fffffffe540, x=...) at
/home/acm/Documents/Develop/externals/clang-toolchain/src/libcxx/src/locale.cpp:530
#10 0x0000000000401e8a in init (this=0x7fffffffe310,
__sb=0x7fffffffe2a8) at /home/acm/opt/include/c++/v1/ios:660
#11 basic_istream (this=0x0, vtt=0x7fffffffe660, __sb=0x7fffffffe2a8,
this=0x0, vtt=0x7fffffffe660) at
/home/acm/opt/include/c++/v1/istream:294
#12 basic_ios (this=0x7ffff7e109c0, this=0x7ffff7e109c0, vtt=0x404788,
__sb=0x7fffffffe2a8, this=0x7ffff7e109c0, __wch=32767) at
/home/acm/opt/include/c++/v1/istream:1488
#13 basic_stringstream (this=0x7fffffffe290, __wch=24) at
/home/acm/opt/include/c++/v1/sstream:809
#14 main (argc=1, argv=0x7fffffffe668) at ./test.cpp:26
(gdb)

In addition to my trivial test case, many of the libc++abi and libc++
unit tests fail with similar exceptions when r160604 is applied.

If I revert libc++ back to r160594 things start working again.

The rest of toolchain was built with the following component revisions:
llvm: r160611
clang: r160613
libc++abi: r160553

It is not immediately obvious to me how r160604's noexcept and
constexpr changes to std::mutex could cause this. Valgrind didn't have
anything interesting to say. Any suggestions about where to start
looking?

Thanks,
Andrew