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Message-ID: <20200602014227.GM31009@gate.crashing.org>
Date: Mon, 1 Jun 2020 20:42:27 -0500
From: Segher Boessenkool <segher@...nel.crashing.org>
To: Joseph Myers <joseph@...esourcery.com>
Cc: Will Springer <skirmisher@...tonmail.com>, libc-alpha@...rceware.org,
eery@...erfox.es, daniel@...aforge.org, musl@...ts.openwall.com,
binutils@...rceware.org, libc-dev@...ts.llvm.org,
linuxppc-dev@...ts.ozlabs.org
Subject: Re: ppc64le and 32-bit LE userland compatibility
Hi Joseph,
On Mon, Jun 01, 2020 at 09:28:25PM +0000, Joseph Myers wrote:
> On Fri, 29 May 2020, Will Springer via Binutils wrote:
>
> > Hey all, a couple of us over in #talos-workstation on freenode have been
> > working on an effort to bring up a Linux PowerPC userland that runs in 32-bit
> > little-endian mode, aka ppcle. As far as we can tell, no ABI has ever been
> > designated for this (unless you count the patchset from a decade ago [1]), so
> > it's pretty much uncharted territory as far as Linux is concerned. We want to
> > sync up with libc and the relevant kernel folks to establish the best path
> > forward.
>
> As a general comment on the glibc side of things, if this is considered
> like a new port, and it probably is, the same principles that apply to new
> ports apply here.
>
> There's a general discussion at
> <https://sourceware.org/glibc/wiki/NewPorts>, although much of that is
> only applicable when adding new CPU architecture support. More specific
> points include that new 32-bit ports should default to 64-bit time and
> file offsets from the start, with no support for 32-bit time or offsets
> (meaning that if you want to use this with some kind of library call
> translation, the library call translation will need to deal with
> corresponding type size conversions).
Either that, or use the same as BE 32-bit PowerPC Linux, I'd say (it
won't make things worse, and if it is easier?) But preferably the
newer, better, thing of course :-)
> And a new port should not be added
> that uses the IBM long double format. You can use IEEE binary128 long
> double, possibly with an ABI similar to that used on powerpc64le, or can
> use long double = double, but should not support IBM long double, and
> preferably should only have one long double format rather than using the
> glibc support for building with different options resulting in functions
> for different long double formats being called.
You cannot use IEEE QP float ("binary128") here, but more on that in a
later post.
(I so very much agree about the problems having more than one long
double format -- on the other hand, you'll just share it with BE, and
with the existing powerpcle-linux (sup)port).
Segher
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