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

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Message-ID: <c8987b31-ed79-acef-a300-31ebf2c29d2e@petrovitsch.priv.at>
Date:   Fri, 14 Dec 2018 15:13:10 +0100
From:   Bernd Petrovitsch <bernd@...rovitsch.priv.at>
To:     Rich Felker <dalias@...c.org>,
        John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
Cc:     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>,
        Florian Weimer <fweimer@...hat.com>,
        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 13/12/2018 17:02, Rich Felker wrote:
> On Tue, Dec 11, 2018 at 11:29:14AM +0100, John Paul Adrian Glaubitz wrote:
>> I can't say anything about the syscall interface. However, what I do know
>> is that the weird combination of a 32-bit userland with a 64-bit kernel
>> interface is sometimes causing issues. For example, application code usually
>> expects things like time_t to be 32-bit on a 32-bit system. However, this

IMHO this just historically grown (as in "it has been forever that way"
- it sounds way better in Viennese dialect though;-).

>> isn't the case for x32 which is why code fails to build.
> 
> I don't see any basis for this claim about expecting time_t to be
> 32-bit. I've encountered some programs that "implicitly assume" this
> by virtue of assuming they can cast time_t to long to print it, or
> similar. IIRC this was an issue in busybox at one point; I'm not sure
> if it's been fixed. But any software that runs on non-Linux unices has
> long been corrected. If not, 2038 is sufficiently close that catching
> and correcting any such remaining bugs is more useful than covering
> them up and making the broken code work as expected.

Yup, unconditionally providing 64bit
time_t/timespec/timeval/...-equivalents with libc and syscall support
also for 32bit architectures (and deprecating all 32bit versions) should
be the way to go.

FWIW I have
----  snip  ----
#if defined __x86_64__
# if defined __ILP32__		// x32
#  define PRI_time_t	"lld"	// for time_t
#  define PRI_nsec_t	"lld"	// for tv_nsec in struct timespec
# else				// x86_64
#  define PRI_time_t	"ld"	// for time_t
#  define PRI_nsec_t	"ld"	// for tv_nsec in struct timespec
# endif
#else				// i[3-6]68
# define PRI_time_t	"ld"	// for time_t
# define PRI_nsec_t	"ld"	// for tv_nsec in struct timespec
#endif
----  snip  ----
in my userspace code for printf() and friends - I don't know how libc's
react to such a patch (and I don't care for the name of the macros as
long it's obviously clear for which type they are).
I assume/fear we won't get additional modifiers into the relevant
standards for libc types (as they are far more like pid_t, uid_t etc.).
And casting to u/intmaxptr_t to get a defined printf()-modifier doesn't
look appealing to me to "solve" such issues.

MfG,
	Bernd
-- 
"I dislike type abstraction if it has no real reason. And saving
on typing is not a good reason - if your typing speed is the main
issue when you're coding, you're doing something seriously wrong."
    - Linus Torvalds

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