CentOS - May 2016 - devtoolset-4

Hello,
my name is Jarek I am new here. I need some clarifications on how to
distribute an app developed with devtoolset-4 enabled.

 I am developing a distributed app in c++ I wanted to upgrade toolchain to
use new standard.
Is it true that when I compile on centos 6.x with devtoolset enabled then I
will be able to run this app on centos 7.x as well?

Do I have to  install devtoolset on all my machines that I want to run this
app? Or would it use built-in libstdc++ library, linking statically only
the missing parts?

This confuses me a bit.

Regards,
-Jarek

On May 19, 2016, at 3:30 AM, Jaros?aw Bober <jaroslaw.bober at gmail.com>
wrote:
> 
> Do I have to  install devtoolset on all my machines that I want to run this
> app?
Probably, yes.  That, or redistribute parts of it with your app, either by
cherrypicking files from the devtoolset RPM or statically linking to it.
> Or would it use built-in libstdc++ library, linking statically only
> the missing parts?
Are you asking if the new libstdc++ is statically linked into your app only for
the new functions but your app remains dynamically linked to the old one for the
parts of C++ that have remained unchanged, the answer is ?no?.  Your app is
linked to the new library, period.  You can use ldd(1) to prove this to
yourself.

Yes, this is a pain, which is why most people writing software for older CentOS
releases don?t upgrade their development tools.  There?s a lot to be said for
holding off on using new language features until they?re available in the stock
version of the tools for all OSes you need to deploy on.

I?d like to be using C++11 myself, but a feature-complete version of C++11
didn?t appear in g++ until 4.8, which first shipped in CentOS 7.  I just got
done backporting a feature to a 32-bit CentOS 5 box, so I?m probably not going
to be able to use C++11 for another 3-5 years.  Sad, but I still get the work
done with C++98.

Are you asking if the new libstdc++ is statically linked into your app only
for the new functions but your app remains dynamically linked to the old
one for the parts of C++ that have remained unchanged, the answer is ?no?.
Your app is linked to the new library, period.  You can use ldd(1) to prove
this to yourself.
I am not so sure.
That is what I thought, but then I compiled something with a compiler from
devtoolset (5.2.1) with --std=c++11 flag.

ldd gives me:
ldd a.out
linux-vdso.so.1 =>  (0x00007fff6e5ff000)
libstdc++.so.6 => /usr/lib64/libstdc++.so.6 (0x00000039d8400000)
libm.so.6 => /lib64/libm.so.6 (0x00000039ce800000)
libgcc_s.so.1 => /lib64/libgcc_s.so.1 (0x00000039d8000000)
libc.so.6 => /lib64/libc.so.6 (0x00000039ce000000)
/lib64/ld-linux-x86-64.so.2 (0x00000039cdc00000)

Which is stock libstdc++
Devtoolset version is located at:
/opt/rh/devtoolset-4/root/usr/lib/gcc/x86_64-redhat-linux/5.2.1/libstdc++.so
Additionally there is libstdc++_nonshared.a:
/opt/rh/devtoolset-4/root/usr/lib/gcc/x86_64-redhat-linux/5.2.1/libstdc++_nonshared.a

In the guide there is a matrix of compatibility:
https://access.redhat.com/documentation/en-US/Red_Hat_Developer_Toolset/4/html/User_Guide/sect-Red_Hat_Developer_Toolset-Compatibility.html
it says that If I compile with DTS on 6.6 thet it will run on 6.6 and
above, but it doesn't say if DTS has to be installed on that machine.
So this got me to thinking.
I definitelly will check that :) and I really believe that it can be this
way. Althought it sounds like black magic.

Regards,
-Jarek

2016-05-19 23:02 GMT+02:00 Warren Young <wyml at etr-usa.com>:
> On May 19, 2016, at 3:30 AM, Jaros?aw Bober <jaroslaw.bober at
gmail.com>
> wrote:
> >
> > Do I have to  install devtoolset on all my machines that I want to run
> this
> > app?
>
> Probably, yes.  That, or redistribute parts of it with your app, either by
> cherrypicking files from the devtoolset RPM or statically linking to it.
>
> > Or would it use built-in libstdc++ library, linking statically only
> > the missing parts?
>
> Are you asking if the new libstdc++ is statically linked into your app
> only for the new functions but your app remains dynamically linked to the
> old one for the parts of C++ that have remained unchanged, the answer is
> ?no?.  Your app is linked to the new library, period.  You can use ldd(1)
> to prove this to yourself.
>
> Yes, this is a pain, which is why most people writing software for older
> CentOS releases don?t upgrade their development tools.  There?s a lot to be
> said for holding off on using new language features until they?re available
> in the stock version of the tools for all OSes you need to deploy on.
>
> I?d like to be using C++11 myself, but a feature-complete version of C++11
> didn?t appear in g++ until 4.8, which first shipped in CentOS 7.  I just
> got done backporting a feature to a 32-bit CentOS 5 box, so I?m probably
> not going to be able to use C++11 for another 3-5 years.  Sad, but I still
> get the work done with C++98.
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