linux-kernel - Re: [PATCH v6 13/17] arm64:ilp32: add sys_ilp32.c and a separate table (in entry.S) to use it

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Message-ID: <4814795.z9jdqoW8IP@wuerfel>
Date:	Mon, 16 Nov 2015 12:00:17 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Joseph Myers <joseph@...esourcery.com>
Cc:	Chris Metcalf <cmetcalf@...hip.com>,
	linux-arm-kernel@...ts.infradead.org, bamvor.zhangjian@...wei.com,
	Andrew Pinski <pinskia@...il.com>,
	"Kapoor, Prasun" <Prasun.Kapoor@...iumnetworks.com>,
	Andreas Schwab <schwab@...e.de>,
	Nathan Lynch <Nathan_Lynch@...tor.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Alexander Graf <agraf@...e.de>,
	Alexey Klimov <klimov.linux@...il.com>, broonie@...nel.org,
	Yury Norov <ynorov@...iumnetworks.com>,
	Andrew Pinski <apinski@...ium.com>,
	David Daney <ddaney.cavm@...il.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Jan Dakinevich <jan.dakinevich@...il.com>,
	Philipp Tomsich <philipp.tomsich@...obroma-systems.com>,
	Andrey Konovalov <andrey.konovalov@...aro.org>,
	christoph.muellner@...obroma-systems.com,
	Mike Frysinger <vapier@...too.org>,
	Paul Eggert <eggert@...ucla.edu>, Rich Felker <dalias@...c.org>
Subject: Re: [PATCH v6 13/17] arm64:ilp32: add sys_ilp32.c and a separate table (in entry.S) to use it

On Monday 16 November 2015 10:16:35 Joseph Myers wrote:
> On Sun, 15 Nov 2015, Chris Metcalf wrote:
> 
> > I've added Rich, Paul, Joseph, and Mike to the cc's as they are probably 
> > a good subset of libc-alpha to help comment on these issues.  My sense 
> > is that right now, it wouldn't be possible to add a 32-bit architecture 
> > with a non-32-bit default for _FILE_OFFSET_BITS.  And, obviously, this 
> > is why, when I added the tilegx32 APIs to glibc in 2011, I needed to 
> > provide _FILE_OFFSET_BITS=32 support.
> 
> x32 uses 64-bit off_t only.  That's not a problem; the problems are 
> tv_nsec not of type long, a bug we should avoid for all new ports (padding 
> on tv_nsec is fine; treating that padding as a significant high part of a 
> 64-bit value on input to glibc / kernel interfaces isn't), and maybe some 
> other types being 64-bit unnecessarily, although as far as I know the 
> suggested issues there 
> <https://sourceware.org/bugzilla/show_bug.cgi?id=16438> are all 
> theoretical.

Let's not get into the tv_nsec discussion today, that is not thankfully
not relevant for arm64 any more at this point. The system call ABI for
arm64/ilp32 is now the same as for any other 32-bit architecture using
the generic ABI, the question we're trying to solve here is only whether it
is ok for new 32-bit glibc ports to only offer a 64-bit off_t as the kernel
currently does (using __kernel_loff_t) or if we still need to support the
_FILE_OFFSET_BITS=32 case.

If I got you right, we can use 64-bit off_t now, so we just need someone
to figure out how to make that the default in glibc for new architectures
while keeping the existing 32-bit architectures unchanged.

	Arnd
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