linux-kernel - Re: [RFC] ARM: kernel: irq: Simplify allocation of stack frame

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <5252E113.3080301@ti.com>
Date:	Mon, 7 Oct 2013 11:28:03 -0500
From:	Joel Fernandes <joelf@...com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, <linux-omap@...r.kernel.org>,
	Nicolas Pitre <nico@...aro.org>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	Jonathan Austin <jonathan.austin@....com>,
	André Hentschel 
	<nerv@...ncrow.de>
Subject: Re: [RFC] ARM: kernel: irq: Simplify allocation of stack frame

On 10/06/2013 05:41 PM, Russell King - ARM Linux wrote:
> On Sun, Oct 06, 2013 at 05:30:47PM -0500, Joel Fernandes wrote:
>> On receiving IRQ exception in SVC mode, all the SVC mode registers are saved
>> onto the stack very early on.
>>
>> The stack frame allocation code for IRQ entry during SVC mode (svc_entry) is
>> hard to read as 4-less is allocated initially only to be allocated later
>> implicity using the mov r3, [sp, #-4]! instruction. We make code easier to read
>> by allocating the 4 bytes on the stack frame in the beginning itself and remove
>> all instances where 4 bytes is adjusted.
> 
> You omit to say that this results in saving one additional register
> unnecessarily in the stmia.  We could use a stmib there instead which
> would avoid that issue while keeping the rest of the change.
> 

Hi Russel,

BTW I used ETM to check the number of cycles used to store the extra register
with and without this patch and with both cases it takes 7 cycles.

My platform uses Cortex-A8 (AM335x SoC).

Thanks,

-Joel
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/