[OE-core] [RFC][PATCH] gcc-runtime.inc: force libstdc++ to always use gcc4 compatible ABI

[Andre McCurdy]

On Tue, Jan 26, 2016 at 8:38 AM, Khem Raj <raj.khem at gmail.com> wrote:
>
>> On Jan 26, 2016, at 12:10 AM, Andre McCurdy <armccurdy at gmail.com> wrote:
>>
>> Experimental hack, not expected to be merged.
>>
>> Without this, the http://www.cplusplus.com/reference/string/string/append/
>> example fails to build with -std=c++11 and it's not clear why (it's as if we
>> build a version of libstdc++ which supports only the old ABI but with headers
>> which try to use the new ABI when compiled with -std=c++11 ?). As a workaround,
>> force libstdc++ to provide, and default to using, the old ABI in all cases.
>>
>> See also:
>>
>>  https://gcc.gnu.org/onlinedocs/libstdc++/manual/configure.html
>>  https://mail.gnome.org/archives/gtkmm-list/2015-June/msg00026.html
>>  https://wiki.debian.org/GCC5
>>
>> Signed-off-by: Andre McCurdy <armccurdy at gmail.com>
>> ---
>> meta/recipes-devtools/gcc/gcc-runtime.inc | 13 +++++++++++++
>> 1 file changed, 13 insertions(+)
>>
>> diff --git a/meta/recipes-devtools/gcc/gcc-runtime.inc b/meta/recipes-devtools/gcc/gcc-runtime.inc
>> index f20d298..3a476cd 100644
>> --- a/meta/recipes-devtools/gcc/gcc-runtime.inc
>> +++ b/meta/recipes-devtools/gcc/gcc-runtime.inc
>> @@ -10,6 +10,19 @@ EXTRA_OECONF_PATHS = "\
>>
>> EXTRA_OECONF_append_linuxstdbase = " --enable-clocale=gnu"
>>
>> +# gcc-runtime.inc: force libstdc++ to always use gcc4 compatible ABI
>> +# Experimental hack. Without this, the http://www.cplusplus.com/reference/string/string/append/
>> +# example fails to build with -std=c++11 and it's not clear why (it's as if we
>> +# build a version of libstdc++ which supports only the old ABI but with headers
>> +# which try to use the new ABI when compiled with -std=c++11 ?). As a workaround,
>> +# force libstdc++ to provide, and default to using, the old ABI in all cases.
>> +# See also:
>> +# https://gcc.gnu.org/onlinedocs/libstdc++/manual/configure.html
>> +# https://mail.gnome.org/archives/gtkmm-list/2015-June/msg00026.html
>> +# https://wiki.debian.org/GCC5
>> +#
>> +EXTRA_OECONF_append = " --disable-libstdcxx-dual-abi --with-default-libstdcxx-abi=gcc4-compatible”
>
> This change while makes it work compatible to older libstdc++ ABI, we should make the defaults to be
> forward looking.

Yes, I agree. The problem is that currently our libstdc++ doesn't seem
to support the new ABI.

> I would rather keep --with-default-libstdcxx-abi=c++11 since gcc6 will switch to newer
> c++ std as default. If we revert like you suggest, we will be up for more work in gcc6 time.
>
> please define _GLIBCXX_USE_CXX11_ABI=0 for your app, where you see the problem.

My test case is the example app from:

  http://www.cplusplus.com/reference/string/string/append/

It fails when I try to compile to use the new ABI (ie by using
-stdc++11 or _GLIBCXX_USE_CXX11_ABI=1).

There is no legacy code involved.

>
>> RUNTIMETARGET = "libssp libstdc++-v3 libgomp libatomic \
>>     ${@bb.utils.contains_any('FORTRAN', [',fortran',',f77'], 'libquadmath', '', d)} \
>> "
>> --
>> 1.9.1
>>
>> --
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