[libc++ patch] Make locales (and transitively, std::endl) work reliably with gcc

[Nico Weber]

Ping?


On Mon, Jun 2, 2014 at 10:11 AM, Nico Weber <thakis at chromium.org> wrote:

> Ping.
>
>
> On Fri, May 30, 2014 at 4:04 PM, Nico Weber <thakis at chromium.org> wrote:
>
>> Hi,
>>
>> on trunk, libc++ relies on undefined initialization order of global
>> initializers when using gcc:
>>
>> 1. __start_std_streams in iostream.cpp calls locale::id::_init, which
>> assigns an id to each locale::facet in an initializer
>>
>> 2. Every facet has a static locale::id id, whose constructor sets the
>> facet's id to 0*
>>
>> If 2 runs after 1, it clobbers the facet's assigned consecutive id,
>> causing exceptions to be thrown when e.g. running code like "cout << endl".
>>
>> To fix this, the attached patch lets _LIBCPP_CONSTEXPR evaluate to
>> "constexpr" instead of nothing with gcc. locale::id's constructor is marked
>> _LIBCPP_CONSTEXPR, which ensures that it won't get an initializer that
>> could potentially run after the iostream.cpp initializer. (This remains
>> broken when building with msvc.)
>>
>> Once _LIBCPP_CONSTEXPR is available, bitset fails to compile since gcc
>> doesn't define __SIZE_WIDTH__, so switch bitset to use __SIZEOF_SIZE_T__
>> which both clang and gcc define.
>>
>> Pair-programmed/debugged with Dana Jansens.
>>
>> Nico
>>
>
>
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