Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755520AbaKSOyl (ORCPT ); Wed, 19 Nov 2014 09:54:41 -0500 Received: from mail-lb0-f178.google.com ([209.85.217.178]:37270 "EHLO mail-lb0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754536AbaKSOyk (ORCPT ); Wed, 19 Nov 2014 09:54:40 -0500 MIME-Version: 1.0 In-Reply-To: <2041617.Kxhx5O4MMr@wuerfel> References: <20141118172146.3784.81151.stgit@buzz> <20141118173413.GB4042@n2100.arm.linux.org.uk> <546B8C64.3010904@samsung.com> <2041617.Kxhx5O4MMr@wuerfel> Date: Wed, 19 Nov 2014 15:54:38 +0100 Message-ID: Subject: Re: [PATCH RFC] ARM: option for loading modules into vmalloc area From: Ard Biesheuvel To: Arnd Bergmann Cc: "linux-arm-kernel@lists.infradead.org" , Andrey Ryabinin , Konstantin Khlebnikov , Russell King - ARM Linux , "linux-kernel@vger.kernel.org" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 19 November 2014 14:40, Arnd Bergmann wrote: > 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? > ARMv6 doesn't support movw/movt so this will only work on v7. What about doing 'mov lr, pc; ldr pc,=symbol' instead? You clearly don't care about performance in this case, so the performance hit (due to the dcache access and interfering with the return stack predictors) should be tolerable. The only thing to be careful about is thumb2 kernels: you would need to set the thumb bit in lr manually but only if the call is made /from/ thumb. You would probably be better off just depending on !THUMB2_KERNEL. -- Ard. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/