This is the mail archive of the
mailing list for the glibc project.
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 13:21:45 -0700 (PDT)
- Subject: Re: [PATCH 01/23] all: syscall wrappers: add documentation
- Authentication-results: sourceware.org; auth=none
- References: <1464048292-30136-2-git-send-email-ynorov at caviumnetworks dot com> <20160525 dot 123017 dot 1597296248000772613 dot davem at davemloft dot net> <20160525200327 dot GA22395 at yury-N73SV>
From: Yury Norov <firstname.lastname@example.org>
Date: Wed, 25 May 2016 23:03:27 +0300
> On Wed, May 25, 2016 at 12:30:17PM -0700, David Miller wrote:
>> From: Yury Norov <email@example.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.
> It was discussed as one of possible solutions. The downside of it is
> that we cannot pass 64-bit types (like off_t) in single register.
Wrappers can be added for the cases where you'd like to do that.
> The other downside is that we clear top halves for every single
> syscall, and it looks excessive. So, from spark64 and s390 approaches
> we choosed second.
It's like 4 cpu cycles even on crappy sparc64 cpus which only dual
And that's a pretty low cost for the benefits if you ask me.