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Message-ID: <20190121120224.GS21289@port70.net>
Date: Mon, 21 Jan 2019 13:02:24 +0100
From: Szabolcs Nagy <nsz@...t70.net>
To: musl@...ts.openwall.com,
Michele Portolan <michele.portolan@...noble-inp.fr>
Subject: Re: New to musl and C++ compiling
* 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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