linux-kernel - Re: [PATCH RFC] ARM: option for loading modules into vmalloc area

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Date:	Wed, 19 Nov 2014 14:40:49 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	Konstantin Khlebnikov <k.khlebnikov@...sung.com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Andrey Ryabinin <a.ryabinin@...sung.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] ARM: option for loading modules into vmalloc area

On Tuesday 18 November 2014 21:13:56 Konstantin Khlebnikov wrote:
> On 2014-11-18 20:34, Russell King - ARM Linux wrote:
> > On Tue, Nov 18, 2014 at 08:21:46PM +0400, Konstantin Khlebnikov wrote:
> >> Usually modules are loaded into small area prior to the kernel
> >> text because they are linked with the kernel using short calls.
> >> Compile-time instrumentation like GCOV or KASAN bloats code a lot,
> >> and as a result huge modules no longer fit into reserved area.
> >>
> >> This patch adds option CONFIG_MODULES_USE_VMALLOC which lifts
> >> limitation on amount of loaded modules. It links modules using
> >> long-calls (option -mlong-calls) and loads them into vmalloc area.
> >>
> >> In few places exported symbols are called from inline assembly.
> >> This patch adds macro for such call sites: __asmbl and __asmbl_clobber.
> >> Call turns into single 'bl' or sequence 'movw; movt; blx' depending on
> >> context and state of config option.
> >>
> >> Unfortunately this option isn't compatible with CONFIG_FUNCTION_TRACER.
> >> Compiler emits short calls to profiling function despite of -mlong-calls.
> >> This is a bug in GCC, but ftrace anyway needs an update to handle this.
> > It also isn't compatible with the older architectures which don't have
> > "blx".
> 
> Ok, I'll add "depends on CPU_V6 || CPU_V7" I don't think that it is 
> necessary for older cpus.

Why not just use a different branch instruction for the older CPUs?

	Arnd
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