linux-kernel - Re: [C/R ARM][PATCH 1/3] ARM: Rudimentary syscall interfaces

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Message-ID: <20100324020342.GB5704@count0.beaverton.ibm.com>
Date:	Tue, 23 Mar 2010 19:03:42 -0700
From:	Matt Helsley <matthltc@...ibm.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Christoffer Dall <christofferdall@...istofferdall.dk>,
	Roland McGrath <roland@...hat.com>,
	containers <containers@...ts.linux-foundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [C/R ARM][PATCH 1/3] ARM: Rudimentary syscall interfaces

On Tue, Mar 23, 2010 at 08:53:42PM +0000, Russell King - ARM Linux wrote:
> On Sun, Mar 21, 2010 at 09:06:03PM -0400, Christoffer Dall wrote:
> > This small commit introduces a global state of system calls for ARM
> > making it possible for a debugger or checkpointing to gain information
> > about another process' state with respect to system calls.
> 
> I don't particularly like the idea that we always store the syscall
> number to memory for every system call, whether the stored version is
> used or not.
> 
> Since ARM caches are generally not write allocate, this means mostly
> write-only variables can have a higher than expected expense.
> 
> Is there not some thread flag which can be checked to see if we need to
> store the syscall number?

Perhaps before we freeze the task we can save the syscall number on ARM.
The patches suggest that the signal delivery path -- which the freezer
utilizes -- has the syscall number already.

Should work since the threads must be frozen first anyway.

Cheers,
	-Matt Helsley
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