New to musl and C++ compiling

New to musl and C++ compiling

[Michele Portolan]

Hello,

I just installed MUSL because I have a C++ multithreaded application 
that uses threads heavily and I would like to make it independent from 
an OS. I was able to easily install and run MUSL for C targets, but when 
I try a simple C++ Hello world I get an error for the standard libs.

My file is the simplest possible (no multithreading to start with):

  #include <iostream>

  int main() {
           std::cout << "Hello, World" << std::endl;
           return 0;
}

Here is my output for standard and musl-based compilation.

portolan@noumea:~/musl/examples$ g++ -o test_cpp test_cpp.cpp
portolan@noumea:~/musl/examples$ ./test_cpp
Hello, World
portolan@noumea:~/musl/examples$ g++ -o test_cpp test_cpp.cpp -specs 
"/home/portolan/musl/install/lib/musl-gcc.specs"
test_cpp.cpp:1:11: fatal error: iostream: No such file or directory
   #include <iostream>
            ^~~~~~~~~~
compilation terminated.

I am probably missing something REALLY basic, at least I hope so!

Best regards,


Michele

Re: New to musl and C++ compiling

[Szabolcs Nagy]

* Michele Portolan <michele.portolan@grenoble-inp.fr> [2019-01-21 11:24:12 +0100]:
> Hello,
> 
> I just installed MUSL because I have a C++ multithreaded application that
> uses threads heavily and I would like to make it independent from an OS. I
> was able to easily install and run MUSL for C targets, but when I try a
> simple C++ Hello world I get an error for the standard libs.
> 
> My file is the simplest possible (no multithreading to start with):
> 
>  #include <iostream>
> 
>  int main() {
>           std::cout << "Hello, World" << std::endl;
>           return 0;
> }
> 
> Here is my output for standard and musl-based compilation.
> 
> portolan@noumea:~/musl/examples$ g++ -o test_cpp test_cpp.cpp
> portolan@noumea:~/musl/examples$ ./test_cpp
> Hello, World
> portolan@noumea:~/musl/examples$ g++ -o test_cpp test_cpp.cpp -specs
> "/home/portolan/musl/install/lib/musl-gcc.specs"

for c++ the recommended practice is to use a cross compiler that
is built for musl, instead of a glibc based native compiler with
a specs file or other wrapping mechanism, because c++ headers are
difficult to get right: in this case the specs file disabled all
c++ header paths, you need to add those back manually, see

g++ -v -E -xc++ - </dev/null

but there may be still issues
- the header ordering matters as libstdc++ uses include_next and
- some headers are installed based on the libc found at configure
  time of gcc, so the abi is slightly different depending on what
  libc you built your compiler for,
- e.g. with static linking (which you need if you want a portable
  executable) one issue is that libstdc++ has a broken way to
  detect multi-threadedness and all locks become nops (unless your
  binary has a definition for the 'pthread_cancel' symbol).
  if gcc is configured for *-musl* this is fixed.

in short: use a cross compiler targetting *-linux-musl, there are
prebuilt ones at http://musl.cc/
(note that you will have to build and install all your application
dependencies into a path where the cross compiler can find them)


> test_cpp.cpp:1:11: fatal error: iostream: No such file or directory
>   #include <iostream>
>            ^~~~~~~~~~
> compilation terminated.
> 
> I am probably missing something REALLY basic, at least I hope so!
> 
> Best regards,
> 
> 
> Michele

Re: New to musl and C++ compiling

[Szabolcs Nagy]

* Szabolcs Nagy <nsz@port70.net> [2019-01-21 12:53:13 +0100]:

> * Michele Portolan <michele.portolan@grenoble-inp.fr> [2019-01-21 11:24:12 +0100]:
> > Hello,
> > 
> > I just installed MUSL because I have a C++ multithreaded application that
> > uses threads heavily and I would like to make it independent from an OS. I
> > was able to easily install and run MUSL for C targets, but when I try a
> > simple C++ Hello world I get an error for the standard libs.
> > 
> > My file is the simplest possible (no multithreading to start with):
> > 
> >  #include <iostream>
> > 
> >  int main() {
> >           std::cout << "Hello, World" << std::endl;
> >           return 0;
> > }
> > 
> > Here is my output for standard and musl-based compilation.
> > 
> > portolan@noumea:~/musl/examples$ g++ -o test_cpp test_cpp.cpp
> > portolan@noumea:~/musl/examples$ ./test_cpp
> > Hello, World
> > portolan@noumea:~/musl/examples$ g++ -o test_cpp test_cpp.cpp -specs
> > "/home/portolan/musl/install/lib/musl-gcc.specs"
> 
> for c++ the recommended practice is to use a cross compiler that
> is built for musl, instead of a glibc based native compiler with
> a specs file or other wrapping mechanism, because c++ headers are
> difficult to get right: in this case the specs file disabled all
> c++ header paths, you need to add those back manually, see
> 
> g++ -v -E -xc++ - </dev/null
> 
> but there may be still issues
> - the header ordering matters as libstdc++ uses include_next and
> - some headers are installed based on the libc found at configure
>   time of gcc, so the abi is slightly different depending on what
>   libc you built your compiler for,
> - e.g. with static linking (which you need if you want a portable
>   executable) one issue is that libstdc++ has a broken way to
>   detect multi-threadedness and all locks become nops (unless your
>   binary has a definition for the 'pthread_cancel' symbol).
>   if gcc is configured for *-musl* this is fixed.
> 
> in short: use a cross compiler targetting *-linux-musl, there are
> prebuilt ones at http://musl.cc/
> (note that you will have to build and install all your application
> dependencies into a path where the cross compiler can find them)

oh and if you have many dependencies then the simplest way is of
course to use a musl based distro (alpine, void, adelie,..) then
you can use all the prebuilt packages and the native toolchain
with g++ -static and you get a portable executable.
(setting up a chroot or docker with whatever distro should not be
too much work).

> > test_cpp.cpp:1:11: fatal error: iostream: No such file or directory
> >   #include <iostream>
> >            ^~~~~~~~~~
> > compilation terminated.
> > 
> > I am probably missing something REALLY basic, at least I hope so!
> > 
> > Best regards,
> > 
> > 
> > Michele

Re: New to musl and C++ compiling

[Michele Portolan]

Thanks for the information.

You say "use a cross compiler that is built for musl" ... how do I do this?

Binaries are useful, but if I can also get the build process right it is 
more powerful, and easier to pass to students (I am an academic).

Thanks,


Michele

On 21/01/2019 13:02, Szabolcs Nagy wrote:
> * Szabolcs Nagy <nsz@port70.net> [2019-01-21 12:53:13 +0100]:
>
>> * Michele Portolan <michele.portolan@grenoble-inp.fr> [2019-01-21 11:24:12 +0100]:
>>> Hello,
>>>
>>> I just installed MUSL because I have a C++ multithreaded application that
>>> uses threads heavily and I would like to make it independent from an OS. I
>>> was able to easily install and run MUSL for C targets, but when I try a
>>> simple C++ Hello world I get an error for the standard libs.
>>>
>>> My file is the simplest possible (no multithreading to start with):
>>>
>>>   #include <iostream>
>>>
>>>   int main() {
>>>            std::cout << "Hello, World" << std::endl;
>>>            return 0;
>>> }
>>>
>>> Here is my output for standard and musl-based compilation.
>>>
>>> portolan@noumea:~/musl/examples$ g++ -o test_cpp test_cpp.cpp
>>> portolan@noumea:~/musl/examples$ ./test_cpp
>>> Hello, World
>>> portolan@noumea:~/musl/examples$ g++ -o test_cpp test_cpp.cpp -specs
>>> "/home/portolan/musl/install/lib/musl-gcc.specs"
>> for c++ the recommended practice is to use a cross compiler that
>> is built for musl, instead of a glibc based native compiler with
>> a specs file or other wrapping mechanism, because c++ headers are
>> difficult to get right: in this case the specs file disabled all
>> c++ header paths, you need to add those back manually, see
>>
>> g++ -v -E -xc++ - </dev/null
>>
>> but there may be still issues
>> - the header ordering matters as libstdc++ uses include_next and
>> - some headers are installed based on the libc found at configure
>>    time of gcc, so the abi is slightly different depending on what
>>    libc you built your compiler for,
>> - e.g. with static linking (which you need if you want a portable
>>    executable) one issue is that libstdc++ has a broken way to
>>    detect multi-threadedness and all locks become nops (unless your
>>    binary has a definition for the 'pthread_cancel' symbol).
>>    if gcc is configured for *-musl* this is fixed.
>>
>> in short: use a cross compiler targetting *-linux-musl, there are
>> prebuilt ones at http://musl.cc/
>> (note that you will have to build and install all your application
>> dependencies into a path where the cross compiler can find them)
> oh and if you have many dependencies then the simplest way is of
> course to use a musl based distro (alpine, void, adelie,..) then
> you can use all the prebuilt packages and the native toolchain
> with g++ -static and you get a portable executable.
> (setting up a chroot or docker with whatever distro should not be
> too much work).
>
>>> test_cpp.cpp:1:11: fatal error: iostream: No such file or directory
>>>    #include <iostream>
>>>             ^~~~~~~~~~
>>> compilation terminated.
>>>
>>> I am probably missing something REALLY basic, at least I hope so!
>>>
>>> Best regards,
>>>
>>>
>>> Michele

Re: New to musl and C++ compiling

[Szabolcs Nagy]

* Michele Portolan <michele.portolan@grenoble-inp.fr> [2019-01-21 14:13:07 +0100]:
> Thanks for the information.
> 
> You say "use a cross compiler that is built for musl" ... how do I do this?

build gcc for x86_64-linux-musl target, there are some subtleties,
so it may be easier to use an existing build script such as

https://github.com/richfelker/musl-cross-make

and then

make -j$(nproc) TARGET=x86_64-linux-musl install

and then use "output/bin/x86_64-linux-musl-g++ -static"

> 
> Binaries are useful, but if I can also get the build process right it is
> more powerful, and easier to pass to students (I am an academic).
> 
> Thanks,
> 
> 
> Michele
> 
> On 21/01/2019 13:02, Szabolcs Nagy wrote:
> > * Szabolcs Nagy <nsz@port70.net> [2019-01-21 12:53:13 +0100]:
> > 
> > > * Michele Portolan <michele.portolan@grenoble-inp.fr> [2019-01-21 11:24:12 +0100]:
> > > > Hello,
> > > > 
> > > > I just installed MUSL because I have a C++ multithreaded application that
> > > > uses threads heavily and I would like to make it independent from an OS. I
> > > > was able to easily install and run MUSL for C targets, but when I try a
> > > > simple C++ Hello world I get an error for the standard libs.
> > > > 
> > > > My file is the simplest possible (no multithreading to start with):
> > > > 
> > > >   #include <iostream>
> > > > 
> > > >   int main() {
> > > >            std::cout << "Hello, World" << std::endl;
> > > >            return 0;
> > > > }
> > > > 
> > > > Here is my output for standard and musl-based compilation.
> > > > 
> > > > portolan@noumea:~/musl/examples$ g++ -o test_cpp test_cpp.cpp
> > > > portolan@noumea:~/musl/examples$ ./test_cpp
> > > > Hello, World
> > > > portolan@noumea:~/musl/examples$ g++ -o test_cpp test_cpp.cpp -specs
> > > > "/home/portolan/musl/install/lib/musl-gcc.specs"
> > > for c++ the recommended practice is to use a cross compiler that
> > > is built for musl, instead of a glibc based native compiler with
> > > a specs file or other wrapping mechanism, because c++ headers are
> > > difficult to get right: in this case the specs file disabled all
> > > c++ header paths, you need to add those back manually, see
> > > 
> > > g++ -v -E -xc++ - </dev/null
> > > 
> > > but there may be still issues
> > > - the header ordering matters as libstdc++ uses include_next and
> > > - some headers are installed based on the libc found at configure
> > >    time of gcc, so the abi is slightly different depending on what
> > >    libc you built your compiler for,
> > > - e.g. with static linking (which you need if you want a portable
> > >    executable) one issue is that libstdc++ has a broken way to
> > >    detect multi-threadedness and all locks become nops (unless your
> > >    binary has a definition for the 'pthread_cancel' symbol).
> > >    if gcc is configured for *-musl* this is fixed.
> > > 
> > > in short: use a cross compiler targetting *-linux-musl, there are
> > > prebuilt ones at http://musl.cc/
> > > (note that you will have to build and install all your application
> > > dependencies into a path where the cross compiler can find them)
> > oh and if you have many dependencies then the simplest way is of
> > course to use a musl based distro (alpine, void, adelie,..) then
> > you can use all the prebuilt packages and the native toolchain
> > with g++ -static and you get a portable executable.
> > (setting up a chroot or docker with whatever distro should not be
> > too much work).
> > 
> > > > test_cpp.cpp:1:11: fatal error: iostream: No such file or directory
> > > >    #include <iostream>
> > > >             ^~~~~~~~~~
> > > > compilation terminated.
> > > > 
> > > > I am probably missing something REALLY basic, at least I hope so!
> > > > 
> > > > Best regards,
> > > > 
> > > > 
> > > > Michele