Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932278AbaKSPwm (ORCPT ); Wed, 19 Nov 2014 10:52:42 -0500 Received: from mail-wi0-f182.google.com ([209.85.212.182]:38003 "EHLO mail-wi0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932240AbaKSPwk (ORCPT ); Wed, 19 Nov 2014 10:52:40 -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 19:52:39 +0400 Message-ID: Subject: Re: [PATCH RFC] ARM: option for loading modules into vmalloc area From: Konstantin Khlebnikov To: Ard Biesheuvel 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 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 > Ard. > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel -- 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/