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Re: o32 != n32

On Thu, May 7, 2015 at 6:01 PM, Mathieu Malaterre <malat@debian.org> wrote:
> 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`
> (https://gcc.gnu.org/projects/mipso64-abi.html)
> 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 ?

O32 is like i386,
N32 is like x32
N64 is like x86-64 aka amd64.

N32 and N64 ask for 64bit CPU, while CI20 uses a 32bit only CPU,
so you cannot use N32 and N64 on it.

> 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.

`/usr/lib/mipsel-n32-linux-gnu/` -> /usr/lib/mips64el-linux-gnuabin32

We also have
    /usr/lib/mips64el-linux-gnuabi64 for N64.

> Thanks again for your time and clarification !
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YunQiang Su

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