linux-kernel - Re: [PATCH v4 00/24] ILP32 for ARM64

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Date:	Mon, 04 May 2015 12:29:52 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	"Dr. Philipp Tomsich" <philipp.tomsich@...obroma-systems.com>,
	Andreas Kraschitzer <andreas.kraschitzer@...obroma-systems.com>,
	"Pinski, Andrew" <Andrew.Pinski@...iumnetworks.com>,
	Catalin Marinas <catalin.marinas@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"agraf@...e.de" <agraf@...e.de>,
	Andrew Pinski <apinski@...ium.com>,
	Andreas Schwab <schwab@...e.de>,
	Kumar Sankaran <ksankaran@....com>,
	Benedikt Huber <benedikt.huber@...obroma-systems.com>,
	Christoph Muellner <christoph.muellner@...obroma-systems.com>
Subject: Re: [PATCH v4 00/24] ILP32 for ARM64

On Saturday 18 April 2015 21:24:19 Arnd Bergmann wrote:
> Given Catalin's comments from yesterday, I think we can just fix the
> definitions of 'struct stat64' for asm-generic to make it have the same
> layout as the 64-bit version of 'struct stat', and use that for aarch64-ilp32.
> 
> Similarly for the four sysvipc headers, we can have a modified version of
> the asm-generic ones in arch/arm64/uapi/asm, which will use the same layout
> for ilp32 and lp64 without having to set __kernel_ulong_t to 64-bit.

To pick up that earlier thread, I now have a prototype implementation for
converting all 32-bit architectures to use 64-bit time_t.

For 'struct stat', I ended up introducing a new structure on arm32 that
matches the layout of arm64 (and I did the same for all other 32-bit
architectures that have a 64-bit counterpart). This means we can share
the same system calls between arm64-lp64, arm64-ilp32 and arm32 with
64-bit time_t and arm64-aarch32 emulation for 32-bit time_t, while
using the existing compat handling for the original 'struct stat'
emulation in both arm32 and arm64-aarch32.

However, for ipc, the situation is different: I found a way to use
extra padding fields in semid64_ds/shmid64_ds/msqid64_ds, so the
ipc system calls will still use normal 32-bit data structures
on arm32 and arm64-aarch64, but you cannot use them arm64-ilp32,
and will have to #ifdef the three header files there to choose between
the two implementations.

	Arnd
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