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Date: Mon, 21 Jan 2019 14:55:54 +0100
From: Szabolcs Nagy <nsz@...t70.net>
To: musl@...ts.openwall.com
Subject: Re: New to musl and C++ compiling
* Michele Portolan <michele.portolan@...noble-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$(nproc) TARGET=x86_64-linux-musl install
and then use "output/bin/x86_64-linux-musl-g++ -static"
>
> Binaries are useful, but if I can also get the build process right it is
> more powerful, and easier to pass to students (I am an academic).
>
> Thanks,
>
>
> Michele
>
> On 21/01/2019 13:02, Szabolcs Nagy wrote:
> > * Szabolcs Nagy <nsz@...t70.net> [2019-01-21 12:53:13 +0100]:
> >
> > > * Michele Portolan <michele.portolan@...noble-inp.fr> [2019-01-21 11:24:12 +0100]:
> > > > Hello,
> > > >
> > > > I just installed MUSL because I have a C++ multithreaded application that
> > > > uses threads heavily and I would like to make it independent from an OS. I
> > > > was able to easily install and run MUSL for C targets, but when I try a
> > > > simple C++ Hello world I get an error for the standard libs.
> > > >
> > > > My file is the simplest possible (no multithreading to start with):
> > > >
> > > > #include <iostream>
> > > >
> > > > int main() {
> > > > std::cout << "Hello, World" << std::endl;
> > > > return 0;
> > > > }
> > > >
> > > > Here is my output for standard and musl-based compilation.
> > > >
> > > > portolan@...mea:~/musl/examples$ g++ -o test_cpp test_cpp.cpp
> > > > portolan@...mea:~/musl/examples$ ./test_cpp
> > > > Hello, World
> > > > portolan@...mea:~/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
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