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Re: o32 != n32

On Thu, May 7, 2015 at 11:41 AM, James Cowgill <james410@cowgill.org.uk> wrote:
> On Thu, 2015-05-07 at 11:25 +0200, Mathieu Malaterre wrote:
>> On Thu, May 7, 2015 at 10:57 AM, James Cowgill <james410@cowgill.org.uk> 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`

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

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 ?

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.

Thanks again for your time and clarification !

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