[cfe-dev] libc++ and libc++abi problem with stdexcept on linux

[Alexander Potapenko]

ASan complains about the memory being allocated with operator new[]
for array types (this is probably done in
libcxxabi/src/stdexcept.cpp:78:

 75 __libcpp_nmstr::__libcpp_nmstr(const char* msg)
 76 {
 77     std::size_t len = strlen(msg);
 78     str_ = static_cast<const char*>(::operator new(len + 1 + offset));

) and deallocated with operator delete for non-array types (at
libcxxabi/src/stdexcept.cpp:123:

116 __libcpp_nmstr::~__libcpp_nmstr()
117 {
118 #if __APPLE__
119     if (str_ != get_gcc_empty_string_storage())
120 #endif
121         if (__sync_add_and_fetch(&count(), count_t(-1)) < 0)
122         {
123             ::operator delete(const_cast<char*>(str_ - offset));
124         }

)

Such a mismatch is explicitly considered UB in the C++11 Standard.

Howard, can you please take a look?

On Mon, Dec 30, 2013 at 9:21 AM, Ben Pope <benpope81 at gmail.com> wrote:
> Hi,
>
> I've got libc++ linked with libc++abi, but I'm having a problem within
> stdexcept, it seems to be mixing up the __libcpp_nmstr from libc++ with
> that from libc++abi.
>
> I built trunk libc++ and libc++abi on Ubuntu 13.10 with:
> CC=clang-3.4 CXX=clang++-3.4 cmake -G "Unix Makefiles"
> -DLIBCXX_CXX_ABI=libcxxabi
> -DLIBCXX_LIBCXXABI_INCLUDE_PATHS="../../libcxxabi/include"
> -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=/usr ../
>
>
> The following code reproduces this:
>
> #include <stdexcept>
>
> int main()
> {
>    try { throw std::runtime_error("Foo"); }
>    catch (std::exception const&) {}
> }
>
> clang++-3.4 -fsanitize=address -std=c++11 -stdlib=libc++ -lc++abi
> teststdexcept.cpp -o teststdexcept
>
> And the output of ASan:
>
> =================================================================
> ==12336==ERROR: AddressSanitizer: alloc-dealloc-mismatch (operator new
> [] vs operator delete) on 0x60300000efe0
>     #0 0x466019 in operator delete(void*)
> /home/ben/development/llvm/3.4/final/llvm.src/projects/compiler-rt/lib/asan/asan_new_delete.cc:83
>     #1 0x7f6cbbbca550 in ~__libcpp_nmstr
> /home/ben/development/llvm/trunk/libcxxabi/lib/../src/stdexcept.cpp:123
>     #2 0x7f6cbbbca550 in std::overflow_error::~overflow_error()
> /home/ben/development/llvm/trunk/libcxxabi/lib/../src/stdexcept.cpp:150
>     #3 0x7f6cbbbc6d9d in __cxa_decrement_exception_refcount
> /home/ben/development/llvm/trunk/libcxxabi/lib/../src/cxa_exception.cpp:519
>     #4 0x7f6cbbbc6d9d in __cxa_end_catch
> /home/ben/development/llvm/trunk/libcxxabi/lib/../src/cxa_exception.cpp:399
>     #5 0x47bc1b in main (/home/ben/development/test/teststdexcept+0x47bc1b)
>     #6 0x7f6cba9d9de4 in __libc_start_main
> /build/buildd/eglibc-2.17/csu/libc-start.c:260
>     #7 0x47b77c in _start
> (/home/ben/development/test/teststdexcept+0x47b77c)
>
> 0x60300000efe0 is located 0 bytes inside of 28-byte region
> [0x60300000efe0,0x60300000effc)
> allocated by thread T0 here:
>     #0 0x465dd9 in operator new[](unsigned long)
> /home/ben/development/llvm/3.4/final/llvm.src/projects/compiler-rt/lib/asan/asan_new_delete.cc:54
>     #1 0x7f6cbb02770c in std::runtime_error::runtime_error(char const*)
> (/usr/lib/libc++.so.1+0x9170c)
>     #2 0x7f6cba9d9de4 in __libc_start_main
> /build/buildd/eglibc-2.17/csu/libc-start.c:260
>
>
> Any ideas what went wrong?
>
> Cheers,
>
> Ben
>
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-- 
Alexander Potapenko
Software Engineer
Google Moscow