Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756556AbaKSQCq (ORCPT ); Wed, 19 Nov 2014 11:02:46 -0500 Received: from mail-lb0-f180.google.com ([209.85.217.180]:48320 "EHLO mail-lb0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756140AbaKSQCm (ORCPT ); Wed, 19 Nov 2014 11:02:42 -0500 MIME-Version: 1.0 In-Reply-To: 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 17:02:40 +0100 Message-ID: Subject: Re: [PATCH RFC] ARM: option for loading modules into vmalloc area From: Ard Biesheuvel To: Konstantin Khlebnikov Cc: Arnd Bergmann , Andrey Ryabinin , Konstantin Khlebnikov , Russell King - ARM Linux , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.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 16:52, Konstantin Khlebnikov wrote: > On Wed, Nov 19, 2014 at 5:54 PM, Ard Biesheuvel > wrote: >> 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. > > Do you mean ldr pc, =symbol ? > > In this case I get this error: > > /tmp/ccAHtONU.s: Assembler messages: > /tmp/ccAHtONU.s:220: Error: invalid literal constant: pool needs to be closer > > Probably constant pool doesn't work well in inline assembly. > > > Something like this seems work: > > add lr, pc, #4 > ldr pc, [pc, #-4] > .long symbol > You can add a '.ltorg' instruction which tells the assembler to dump the literal pool, but you still need to jump over it, i.e., adr lr, 0f ldr pc, =symbol .ltorg 0: -- 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/