Loading handle_arch_irq with a PC relative load

[gilles.chanteperdrix@xenomai.org (Gilles Chanteperdrix)]

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.