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 ), 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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