[Buildroot] [PATCH v2] Disable o32 ABI for MIPS64 architectures

[Joshua Kinard <kumba@gentoo.org>]

On 03/26/2014 13:17, Arnout Vandecappelle wrote:
> 
>  Hi Joshua,
> 
> On 26/03/14 15:19, Markos Chandras wrote:
>> On 03/26/2014 12:14 AM, Joshua Kinard wrote:
>>> On 03/25/2014 16:02, Arnout Vandecappelle wrote:
> [snip]
>>>> Support for MIPS o32 ABI on MIPS-64 targets has been removed. Building
>>>> o32 ELF files for MIPS64 is an exotic configuration that nobody should be
>>>> using. If o32 is required, then is better if it's built for MIPS 32-bit
>>>> cores so only 32-bit instructions will be used leading to a more
>>>> efficient o32 usage.
>>>
>>> Just to point out, I wouldn't call this "exotic" -- o32 on mips64 kernels
>>> (MIPS-IV ISA) is what I run on my SGI O2 under Gentoo.  That said, I do
>>> have
>>> a somewhat-working n32 chroot on the same box.  Additionally, isn't o32
> 
>  So the mips64 n32 userspace created by buildroot doesn't work
> completely, just somewhat?

No, "somewhat" means I haven't powered that machine up in a while and
updated it.  It boots into an o32 install I've had since 2005 (and am loathe
to replace just yet, at least as long as the disks stay alive), and I chroot
into a separate n32 root.  It's got an old 350MHz RM7000 CPU (PMC-Sierra),
so updating can take a long time for just the o32 root (gcc is ~17hrs these
days.  Used to be ~2.5hrs in the gcc-3.4.x days).  Once that's updated, I
then update the n32 root.  Almost had that done until a recent snow storm
knocked my power out, and I never resumed the update.


>> We are talking about using 64-bit instructions in *userland* while
>> maintaining the o32 ABI semantics. Well, this is definitely an exotic
>> configuration. We are not talking about 64-bit kernels + o32 userland.
>> An o32 userland usually comes from mips32 and you usually have only
>> 32-bit instructions there.
> 
>  Joshua, if you agree with this reasoning, could you ack Vicente's patch?

Let me get clarification on what "MIPS64" Vincent was referring to first.
It's easy to mix that up.  I was assuming he meant o32 userland + mips64
kernel, which I know still works, even though it is very inefficient (using
just half of your available CPU registers).  If he's referring to the ISA of
MIPS64 (or as I read it, mips64r1/mips64r2), then yeah, it's not a problem
at all.  Though I am not an authority on MIPS' capabilities outside of the
SGI hardware lineup, as that's all that I have available to play with.


-- 
Joshua Kinard
Gentoo/MIPS
kumba at gentoo.org
4096R/D25D95E3 2011-03-28

"The past tempts us, the present confuses us, the future frightens us.  And
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