32 bit musl?

32 bit musl?

[John Mudd]

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I've been using musl on a 32-bit Linux to build 32-bit apps to run on 32
and 64-bit Linux machines. That works well.

I upgraded to a 64 bit development box. I've assumed I would just need to
use -m32 option and I could still build 32 bit apps on my 64 bit machine. I
tried it but it tries to mix 32 & 64 bit code. I guess I was naive.

It looks like I should build a cross compiler? I see several suggestions on
how to do this so I'm not confident this will work well. Or would it be
easier if I just installed a 32 bit Linux in a VM just for building 32 bit
apps with musl?

John

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Re: 32 bit musl?

[Rich Felker]

On Wed, Oct 05, 2016 at 06:20:55PM -0400, John Mudd wrote:
> I've been using musl on a 32-bit Linux to build 32-bit apps to run on 32
> and 64-bit Linux machines. That works well.
> 
> I upgraded to a 64 bit development box. I've assumed I would just need to
> use -m32 option and I could still build 32 bit apps on my 64 bit machine. I
> tried it but it tries to mix 32 & 64 bit code. I guess I was naive.
> 
> It looks like I should build a cross compiler? I see several suggestions on
> how to do this so I'm not confident this will work well. Or would it be
> easier if I just installed a 32 bit Linux in a VM just for building 32 bit
> apps with musl?

GCC's multilib (-m32) is built on the assumption that the same set of
headers can be used. This is generally an invalid assumption, not just
for libc but for third-party libraries whose headers might be in the
include paths too. In principle you could hack on the gcc spec files
to get it to use different include paths for different ABIs, but a
dedicated cross compiler is an easier approach.

Rich

Re: 32 bit musl?

[Shiz]

As Rich noted, a cross-compiler is the easy way out here - GCC multilib has a number of assumptions that break under musl and likely elsewhere.
Since you seem unsure how to compile one, I’d recommend musl-cross-make[1].
You only need to edit a single variable in config.mak and run 'make && make install' to get a working toolchain.

- Shiz

[1]: https://github.com/richfelker/musl-cross-make

> On 06 Oct 2016, at 00:20, John Mudd <johnbmudd@gmail.com> wrote:
> 
> I've been using musl on a 32-bit Linux to build 32-bit apps to run on 32 and 64-bit Linux machines. That works well.
> 
> I upgraded to a 64 bit development box. I've assumed I would just need to use -m32 option and I could still build 32 bit apps on my 64 bit machine. I tried it but it tries to mix 32 & 64 bit code. I guess I was naive.
> 
> It looks like I should build a cross compiler? I see several suggestions on how to do this so I'm not confident this will work well. Or would it be easier if I just installed a 32 bit Linux in a VM just for building 32 bit apps with musl?
> 
> John

Re: 32 bit musl?

[Rich Felker]

On Thu, Oct 06, 2016 at 02:24:43AM +0200, Shiz wrote:
> As Rich noted, a cross-compiler is the easy way out here - GCC multilib has a number of assumptions that break under musl and likely elsewhere.
> Since you seem unsure how to compile one, I’d recommend musl-cross-make[1].
> You only need to edit a single variable in config.mak and run 'make && make install' to get a working toolchain.

You can actually even skip editing/making config.mak with current
versions of mcm. I typically just do something like:

make TARGET=i686-linux-musl OUTPUT=[whatever] -j4 install

Rich


> [1]: https://github.com/richfelker/musl-cross-make
> 
> > On 06 Oct 2016, at 00:20, John Mudd <johnbmudd@gmail.com> wrote:
> > 
> > I've been using musl on a 32-bit Linux to build 32-bit apps to run
> > on 32 and 64-bit Linux machines. That works well.
> > 
> > I upgraded to a 64 bit development box. I've assumed I would just
> > need to use -m32 option and I could still build 32 bit apps on my
> > 64 bit machine. I tried it but it tries to mix 32 & 64 bit code. I
> > guess I was naive.
> > 
> > It looks like I should build a cross compiler? I see several
> > suggestions on how to do this so I'm not confident this will work
> > well. Or would it be easier if I just installed a 32 bit Linux in
> > a VM just for building 32 bit apps with musl?
> > 
> > John

Re: 32 bit musl?

[Jens Staal]

onsdag 5 oktober 2016 kl. 18:20:55 CEST skrev John Mudd:
> I upgraded to a 64 bit development box. I've assumed I would just need to
> use -m32 option and I could still build 32 bit apps on my 64 bit machine. I
> tried it but it tries to mix 32 & 64 bit code. I guess I was naive.

Slightly off-topic but out of curiosity: Would musl theoretically be possible 
to build/use on 16-bit "Linux" (ELKS) with ia16-gcc?

Re: 32 bit musl?

[Rich Felker]

On Thu, Oct 06, 2016 at 09:21:29AM +0200, Jens Staal wrote:
> onsdag 5 oktober 2016 kl. 18:20:55 CEST skrev John Mudd:
> > I upgraded to a 64 bit development box. I've assumed I would just need to
> > use -m32 option and I could still build 32 bit apps on my 64 bit machine. I
> > tried it but it tries to mix 32 & 64 bit code. I guess I was naive.
> 
> Slightly off-topic but out of curiosity: Would musl theoretically be possible 
> to build/use on 16-bit "Linux" (ELKS) with ia16-gcc?

No. There may be a number of individual components you could use on
such a system, but musl implements, and as a whole makes assumptions
that will necessarily be true on, a POSIX-conforming (and somewhat
Linux-flavored) system. In particular POSIX requires 32-bit int. Even
if you had a 16-bit x86 target with 32-bit int, you would need an arch
target for it matching the ABI and things like how TLS works (but I
wonder if anyone ever even figured out TLS on ELKS).

Rich

Re: 32 bit musl?

[John Mudd]

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Many thanks for the help, Shiz and Rich! I've built gcc from source before
but it's a chore. Rich's musl-cross-make was magical. Much better solution
than using a 32-bit VM.

All I need were these  steps. The first two should be obvious but they
tripped me up.
    Make sure gcc AND g++ are installed.
    unset CC
    unzip musl-cross-make-master.zip
    cd musl-cross-make-master
    make TARGET=i686-linux-musl OUTPUT=$(pwd).install -j6 install

So this builds 32-bit executables that use musl libs. It kills two birds
with one stone. That's great.

But it appears to expect musl libc to be installed in /lib for dynamically
linked executables. That's not an option for me. Is there a way I can
override this?

On Wed, Oct 5, 2016 at 6:20 PM, John Mudd <johnbmudd@gmail.com> wrote:

> ...
> It looks like I should build a cross compiler? I see several suggestions
> on how to do this so I'm not confident this will work well. Or would it be
> easier if I just installed a 32 bit Linux in a VM just for building 32 bit
> apps with musl?
>
> John
>

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Re: Re: 32 bit musl?

[Laurent Bercot]

>But it appears to expect musl libc to be installed in /lib for 
>dynamically linked executables. That's not an option for me. Is there a 
>way I can override this?

  You don't need to have the libc itself in /lib, you just need to have a
/lib/ld-musl-i386.so.1 symlink pointing to your 32-bit libc.so (i.e. 
only
the path to the dynamic linker is hardcoded).

  If you have additional 32-bit shared libraries, you can tell the
dynamic linker where to find them by listing their directories in the
/etc/ld-musl-i386.path file.

--
  Laurent

Re: 32 bit musl?

[John Mudd]

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On Sat, Oct 8, 2016 at 9:55 PM, John Mudd <johnbmudd@gmail.com> wrote:

> Rich's musl-cross-make builds 32-bit executables that use musl libs. It
> kills two birds with one stone. That's great.
>
> But it appears to expect musl libc to be installed in /lib for dynamically
> linked executables. That's not an option for me. Is there a way I can
> override this?
>
>
Thanks Laurent, I used symbolic link in /lib for testing on my development
machine. That works well. But I don't have reasonable access to root user
when I deploy for production.

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Re: Re: 32 bit musl?

[Szabolcs Nagy]

* John Mudd <johnbmudd@gmail.com> [2016-10-09 10:29:02 -0400]:
> On Sat, Oct 8, 2016 at 9:55 PM, John Mudd <johnbmudd@gmail.com> wrote:
> 
> > Rich's musl-cross-make builds 32-bit executables that use musl libs. It
> > kills two birds with one stone. That's great.
> >
> > But it appears to expect musl libc to be installed in /lib for dynamically
> > linked executables. That's not an option for me. Is there a way I can
> > override this?
> >
> >
> Thanks Laurent, I used symbolic link in /lib for testing on my development
> machine. That works well. But I don't have reasonable access to root user
> when I deploy for production.

deploy static linked binary or use explicit -Wl,-dynamic-linker

Re: Re: 32 bit musl?

[Bobby Bingham]

On Sun, Oct 09, 2016 at 04:44:44PM +0200, Szabolcs Nagy wrote:
> * John Mudd <johnbmudd@gmail.com> [2016-10-09 10:29:02 -0400]:
> > On Sat, Oct 8, 2016 at 9:55 PM, John Mudd <johnbmudd@gmail.com> wrote:
> > 
> > > Rich's musl-cross-make builds 32-bit executables that use musl libs. It
> > > kills two birds with one stone. That's great.
> > >
> > > But it appears to expect musl libc to be installed in /lib for dynamically
> > > linked executables. That's not an option for me. Is there a way I can
> > > override this?
> > >
> > >
> > Thanks Laurent, I used symbolic link in /lib for testing on my development
> > machine. That works well. But I don't have reasonable access to root user
> > when I deploy for production.
> 
> deploy static linked binary or use explicit -Wl,-dynamic-linker

Using -Wl,-dynamic-linker will result in binaries that will not run on
normal musl systems.

If you can deploy the musl libc alongside your program, you can invoke it
as `/path/to/libc.so /path/to/your/program`.  This can be done by a shell
script you also deploy.

Re: Re: 32 bit musl?

[Rich Felker]

On Sun, Oct 09, 2016 at 10:10:36AM -0500, Bobby Bingham wrote:
> On Sun, Oct 09, 2016 at 04:44:44PM +0200, Szabolcs Nagy wrote:
> > * John Mudd <johnbmudd@gmail.com> [2016-10-09 10:29:02 -0400]:
> > > On Sat, Oct 8, 2016 at 9:55 PM, John Mudd <johnbmudd@gmail.com> wrote:
> > > 
> > > > Rich's musl-cross-make builds 32-bit executables that use musl libs. It
> > > > kills two birds with one stone. That's great.
> > > >
> > > > But it appears to expect musl libc to be installed in /lib for dynamically
> > > > linked executables. That's not an option for me. Is there a way I can
> > > > override this?
> > > >
> > > >
> > > Thanks Laurent, I used symbolic link in /lib for testing on my development
> > > machine. That works well. But I don't have reasonable access to root user
> > > when I deploy for production.
> > 
> > deploy static linked binary or use explicit -Wl,-dynamic-linker
> 
> Using -Wl,-dynamic-linker will result in binaries that will not run on
> normal musl systems.

It will also result in binaries that require the end user to have them
(or at least the dynamic linker part) installed in exactly the same
absolute path that you came up with when building them.

> If you can deploy the musl libc alongside your program, you can invoke it
> as `/path/to/libc.so /path/to/your/program`.  This can be done by a shell
> script you also deploy.

Indeed, this is the recommended approach for shipping dynamic-linked
binaries to be run on non-musl-based systems.

Rich