Re: o32 != n32

James Cowgill <[email protected]> Thu, 07 May 2015 11:21:15 +0100
Newsgroups	gmane.linux.debian.ports.mips
Message-ID	<[email protected]>
On Thu, 2015-05-07 at 12:01 +0200, Mathieu Malaterre wrote:
> On Thu, May 7, 2015 at 11:41 AM, James Cowgill <[email protected]> wrote:
> > On Thu, 2015-05-07 at 11:25 +0200, Mathieu Malaterre wrote:
> >> On Thu, May 7, 2015 at 10:57 AM, James Cowgill <[email protected]> wrote:
> >> > On Thu, 2015-05-07 at 09:27 +0200, Mathieu Malaterre wrote:
> >> >> Hello MIPS gurus,
> >> >>
> >> >> Could someone please let me know if this is possible to have a
> >> >> dual-ABI system (eg: n32 & o32) on MIPS. On my x86-64 system I can run
> >> >> a multi-arch system (x86 & x86-64), thanks to the recent multi-arch
> >> >> effort.
> >> >>
> >> >> Is it possible on MIPS ? Does it make sense ?
> >> >
> >> > If you have a 64-bit kernel then that should completely work (all Debian
> >> > kernels except for 4kc are 64-bit).
> >> >
> >> > If you then install gcc-multilib you should be able to pass -mabi=n32 to
> >> > gcc to get n32 binaries (or -mabi=64 for n64 binaries). I haven't done a
> >> > huge amount of testing with it, but you should also be able to add the
> >> > mips64el debian repo which contains everything recompiled with n64. Then
> >> > you should be able to do proper multiarch.
> >> >
> >> > See: http://mipsdebian.imgtec.com/
> >>
> >> I haven't received my Creator CI20 board yet, but I still fail to
> >> understand how that's possible. On my x86-64 there is a *single* ABI,
> >> and thus I can have a single `/usr/lib/x86_64-linux-gnu/libpthread.so`
> >> installed from libc6-dev:amd64 which wont conflict with
> >> `/usr/lib/i386-linux-gnu/libpthread.so` installed from libc6-dev:i386.
> >
> > The processor in the CI20 is 32-bit only so you won't be able to do any
> > of this on that unfortunately.
> >
> > If you use mipsel / mips64el multiarch, the setup use on amd64 is
> > identical on mips. Multilib places libraries in /lib32 or /lib64 just
> > link it does on x86.
> >
> >> I may sound dumb, but I fail to understand how multi-abi can be
> >> handled when directories are setup to handle (single) per-arch object
> >> files.
> >
> > The directories *are* setup to handle multiple ABIs. 'i386-linux-gnu' is
> > the ABI used on i386 and it is completely different to the
> > 'x86_64-linux-gnu' ABI (you can't link amd64 and i386 objects together).
> 
> My original post was about mixing n32 and o32. So if I try to
> summarize your post (little endian ABI only):
> 
> - debian `mipsel` refers to ABI `o32`
> - debian `mips64el` refers to ABI `o64`
> (https://gcc.gnu.org/projects/mipso64-abi.html)

mips64el uses n64, not o64.

> Debian has not been working officially on any of the n32 or n64 ABIs.

Well it's not in the main archive yet, but there are a number of people
working on it.

> Now let me rephrase my original question into:
> 
> Since Debian `mipsel` is using the old o32 ABI, would it make sense to
> use n32 ABI on Creator CI20 ?

n32 will not work on the CI20 because it only has a 32-bit processor.
n32 is a 64-bit ABI with 32-bit pointers (very similar to x32).

> As per your comment, I will not be able to use (=link to) the o32
> `libc` provided by the default debian `mipsel` package when building
> an n32 application (gcc -mabi=n32). In which case the location
> `/usr/lib/mipsel-linux-gnu/` will be reserved for object files with
> o32 ABI, while something like `/usr/lib/mipsel-n32-linux-gnu/` may be
> used for n32 ABI.

Yes that's correct. Bear in mind that there isn't a n32 debian port so
you'll have to compile any libraries you use (except glibc) yourself.

James
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