linux-kernel - Re: [PATCH 11/27] [AARCH64] Syscalls for ILP32 are passed always via 64bit values.

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Message-ID: <20160622154951.GD6521@e104818-lin.cambridge.arm.com>
Date:	Wed, 22 Jun 2016 16:49:52 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Yury Norov <ynorov@...iumnetworks.com>
Cc:	libc-alpha@...rceware.org, linux-kernel@...r.kernel.org,
	arnd@...db.de, marcus.shawcroft@....com, philb@....org,
	davem@...emloft.net, szabolcs.nagy@....com,
	maxim.kuvyrkov@...aro.org, joseph@...esourcery.com,
	pinskia@...il.com, Andrew Pinski <apinski@...ium.com>
Subject: Re: [PATCH 11/27] [AARCH64] Syscalls for ILP32 are passed always via
 64bit values.

On Tue, Jun 21, 2016 at 08:06:55AM +0300, Yury Norov wrote:
> This patch adds support for ILP32 syscalls, sign and zero extending
> where needed.  Unlike LP64, pointers are 32bit and need to be zero
> extended rather than the standard sign extend that the code would do.
> We take advatage of ssize_t being long rather than int for ILP32,
> to get this correct.

Unless I misunderstand what this patch does, I thought we agreed that
32-bit arguments are passed as 32-bit values and it is the kernel's
responsibility to zero or sign-extend the upper half (IOW, assume
garbage just like the PCS ABI).

We are still debating whether 64-bit values are passed in one or two
registers but this doesn't change the situation of 32-bit values like
pointers.

-- 
Catalin