From mboxrd@z Thu Jan 1 00:00:00 1970 From: gilles.chanteperdrix@xenomai.org (Gilles Chanteperdrix) Date: Fri, 13 Jul 2012 21:51:15 +0200 Subject: Loading handle_arch_irq with a PC relative load In-Reply-To: References: <50007197.8030403@xenomai.org> Message-ID: <50007C33.4000105@xenomai.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 07/13/2012 09:40 PM, Nicolas Pitre wrote: > On Fri, 13 Jul 2012, Gilles Chanteperdrix wrote: > >> >> I do not know if it is really useful, but it seems it would be possible >> to reduce the number of memory accesses to just one in the irq_handler >> macro in the case where CONFIG_MULTI_IRQ_HANDLER is enabled, by using a >> PC relative load, with something like the following patch: > > To be strict with ccode sections, you can't do this. The > handle_arch_irq symbol identifies a variable and with your patch you're > moving it from the .data section to the .text section. The .text > section is meant to be read only, and this is even more true when using > a XIP kernel where .text is in ROM, or if we could make the access > protection of the kernel ro. I understand that but, XIP kernel aside, the handle_arch_irq variable is set only once very early during the boot process, so, almost read-only. Is not Linux using self-modifying code in some cases anyway (booting an SMP kernel on an UP processor for instance). -- Gilles.