Date: Mon, 12 Aug 2019 14:01:19 -0400 From: Rich Felker <dalias@...c.org> To: Paul Eggert <eggert@...ucla.edu> Cc: libc-alpha@...rceware.org, musl@...ts.openwall.com Subject: Re: Re: time64 abi choices for glibc and musl On Sun, Aug 11, 2019 at 09:55:14PM -0400, Rich Felker wrote: > On Sun, Aug 11, 2019 at 05:31:48PM -0700, Paul Eggert wrote: > > Rich Felker wrote: > > >this is a best-effort > > >thing anyway, and can't inherently be expected to work, but the choice > > >that makes things easy on the libc implementation side is *also* the > > >choice that makes this work best. > > > > It doesn't entirely simplify libc, as it enlarges struct stat and > > (more importantly) makes struct stat tricky. This is a judgment > > call, but I would say we're better off in the long run with a > > simpler struct stat that ordinary programmers will understand > > easily, even if this complicates nftw implementation during the > > transition. > > The various archs already have random junk padding in struct stat. Apologies; I was under a longstanding mistaken impression that glibc used the kernel stat64 types, and had per-arch bits headers to provide them, but apparently it doesn't and always uses its own fixed, fairly clean layout (sadly without reserved space for expansion), though. So indeed it would be a little bit of an uglification to add time64-on-32-bit-arch members here. I still think the benefits to minimizing breakage of applications (and avoiding the need for duplicate [n]ftw implementations and symbol redirects, which nobody has proposed doing yet, likely because nobody even realized they would have been needed) are worth it, but my assessment was wrong. This also means whatever glibc decides to do about struct stat is irrelevant to musl's glibc-ABI-compat goals; what I assumed was working now is in fact broken, but doesn't matter because the __xstat shims can fix it up if desired. Rich
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