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Re: [PATCH 01/23] all: syscall wrappers: add documentation
- From: David Miller <davem at davemloft dot net>
- To: catalin dot marinas at arm dot com
- Cc: arnd at arndb dot de, ynorov at caviumnetworks 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: Thu, 26 May 2016 12:43:44 -0700 (PDT)
- Subject: Re: [PATCH 01/23] all: syscall wrappers: add documentation
- Authentication-results: sourceware.org; auth=none
- References: <6407614 dot fdv5XFSBue at wuerfel> <20160525 dot 142821 dot 1719403997976778673 dot davem at davemloft dot net> <20160526142057 dot GA7456 at e104818-lin dot cambridge dot arm dot com>
From: Catalin Marinas <catalin.marinas@arm.com>
Date: Thu, 26 May 2016 15:20:58 +0100
> We can solve (a) by adding more __SC_WRAP annotations in the generic
> unistd.h.
...
I really think it's much more robust to clear the tops of the registers
by default. Then you won't be auditing constantly and adding more and
more wrappers.
You can't even quantify the performance gains for me in any precise
way. Whatever you gain by avoiding the 64-bit
decompostion/reconstitution for those few system calls with 64-bit
registers, you are losing by calling the wrappers for more common
system calls, more often.
"it's more natural to pass 64-bit values in a register" is not a clear
justification for this change.
This looks way over engineered to me.