linux-kernel - Re: Can we drop upstream Linux x32 support?

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Message-ID: <20181214165535.GZ23599@brightrain.aerifal.cx>
Date:   Fri, 14 Dec 2018 11:55:35 -0500
From:   Rich Felker <dalias@...c.org>
To:     Florian Weimer <fweimer@...hat.com>
Cc:     Bernd Petrovitsch <bernd@...rovitsch.priv.at>,
        John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
        Andy Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>,
        Mike Frysinger <vapier@...too.org>,
        "H. J. Lu" <hjl.tools@...il.com>, x32@...ldd.debian.org,
        Arnd Bergmann <arnd@...db.de>,
        Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: Can we drop upstream Linux x32 support?

On Fri, Dec 14, 2018 at 05:38:33PM +0100, Florian Weimer wrote:
> * Rich Felker:
> 
> > This is all useless (and wrong since tv_nsec is required to have type
> > long as part of C and POSIX, regardless of ILP32-vs-LP64; that's a bug
> > in glibc's x32).
> 
> We should be able to fix standards if they prove unworkable in practice.
> In my opinion, if standards require complex solutions where an obvious
> and simple solution exists, then standards are wrong.

The requirement doesn't mandate complex solutions. There's nothing
complex about tv_nsec being long. long is the smallest type that C
guarantees to be large enough to store the range of values, which is
forever fixed and can't grow (because the definition of "nano" prefix
is fixed :). The type has been long ever since the structure was
introduced, and its being long means that there's lots of (correct!)
code using %ld (e.g. ".%.9ld" to format results as a decimal without
using floating point approximations) to print it. There might also be
code taking pointers to it to pass to functions, etc.

The only reason a "complex" need arises is that Linux did something
horribly wrong here, ignoring the specified type, when introducing an
obscure subarch that almost nobody uses. This kind of mistake is
becoming a theme in Linux (see also: msghdr). Application authors
should not have to pay the price for fixing this by retrofitting yet
another silly type like "snseconds_t" or something into programs to
accommodate the mistakes of x32.

Rich