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Re: [PATCH 01/23] all: syscall wrappers: add documentation
- From: David Miller <davem at davemloft dot net>
- To: ynorov at caviumnetworks dot com
- Cc: arnd at arndb dot de, catalin dot marinas at arm dot com, linux-arm-kernel at lists dot infradead dot org, linux-kernel at vger dot kernel dot org, linux-doc at vger dot kernel dot org, linux-arch at vger dot kernel dot org, linux-s390 at vger dot kernel dot org, libc-alpha at sourceware dot org, schwidefsky at de dot ibm dot com, heiko dot carstens at de dot ibm dot com, pinskia at gmail dot com, broonie at kernel dot org, joseph at codesourcery dot com, christoph dot muellner at theobroma-systems dot com, bamvor dot zhangjian at huawei dot com, szabolcs dot nagy at arm dot com, klimov dot linux at gmail dot com, Nathan_Lynch at mentor dot com, agraf at suse dot de, Prasun dot Kapoor at caviumnetworks dot com, kilobyte at angband dot pl, geert at linux-m68k dot org, philipp dot tomsich at theobroma-systems dot com
- Date: Wed, 25 May 2016 12:30:17 -0700 (PDT)
- Subject: Re: [PATCH 01/23] all: syscall wrappers: add documentation
- Authentication-results: sourceware.org; auth=none
- References: <1464048292-30136-1-git-send-email-ynorov at caviumnetworks dot com> <1464048292-30136-2-git-send-email-ynorov at caviumnetworks dot com>
From: Yury Norov <ynorov@caviumnetworks.com>
Date: Tue, 24 May 2016 03:04:30 +0300
> +To clear that top halves, automatic wrappers are introduced. They clear all
> +required registers before passing control to regular syscall handler.
Why have one of these for every single compat system call, rather than
simply clearing the top half of all of these registers unconditionally
in the 32-bit system call trap before the system call is invoked?
That's what we do on sparc64.
And with that, you only need wrappers for the case where there needs
to be proper sign extention of a 32-bit signed argument.