Date: Mon, 1 Jun 2020 17:36:40 -0400 From: Rich Felker <dalias@...c.org> To: Joseph Myers <joseph@...esourcery.com> Cc: Will Springer <skirmisher@...tonmail.com>, linuxppc-dev@...ts.ozlabs.org, libc-alpha@...rceware.org, eery@...erfox.es, daniel@...aforge.org, musl@...ts.openwall.com, binutils@...rceware.org, libc-dev@...ts.llvm.org Subject: Re: Re: ppc64le and 32-bit LE userland compatibility 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). 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. Thanks, these are great points, and the same applies for musl I think. We always have 64-bit off_t anyway, but new ports should have 64-bit time_t to begin with rather than defining _REDIR_TIME64. It's a little bit complicated by the fact that powerpcle would be a "subarch" for powerpc, and we don't yet have any like that where the subarchs' time64 statuses differ, but it doesn't look like that should be hard to do. The arch-specific alltypes.h.in already has access to endianness knowledge. src/ldso/powerpc/dlsym_time64.S would also need added preprocessor conditionals. Exemption from this would be open to discussion if there are existing non-upstream users of powerpcle musl that otherwise complies with ABI policy except for time64, but I'm not aware of any that aren't experimental. Rich
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