Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756032AbaKSQ5U (ORCPT ); Wed, 19 Nov 2014 11:57:20 -0500 Received: from mail-qg0-f45.google.com ([209.85.192.45]:49156 "EHLO mail-qg0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755187AbaKSQ5T (ORCPT ); Wed, 19 Nov 2014 11:57:19 -0500 Date: Wed, 19 Nov 2014 11:57:15 -0500 (EST) From: Nicolas Pitre To: Russell King - ARM Linux cc: Ard Biesheuvel , Konstantin Khlebnikov , Arnd Bergmann , Andrey Ryabinin , Konstantin Khlebnikov , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" Subject: Re: [PATCH RFC] ARM: option for loading modules into vmalloc area In-Reply-To: <20141119164902.GK4042@n2100.arm.linux.org.uk> Message-ID: References: <20141118172146.3784.81151.stgit@buzz> <20141118173413.GB4042@n2100.arm.linux.org.uk> <546B8C64.3010904@samsung.com> <2041617.Kxhx5O4MMr@wuerfel> <20141119160747.GH4042@n2100.arm.linux.org.uk> <20141119164902.GK4042@n2100.arm.linux.org.uk> User-Agent: Alpine 2.11 (LFD 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 19 Nov 2014, Russell King - ARM Linux wrote: > On Wed, Nov 19, 2014 at 11:37:47AM -0500, Nicolas Pitre wrote: > > On Wed, 19 Nov 2014, Russell King - ARM Linux wrote: > > > Which is not a good idea either, because the compiler needs to know how > > > far away its own manually generated literal pool is from the instructions > > > which reference it. The .ltorg statement can end up emitting any number > > > of literals at that point, which makes it indeterminant how many words > > > are contained within the asm() statement. > > > > > > Yes, it isn't desirable to waste an entire data cache line per indirect > > > call like the original quote above, but I don't see a practical > > > alternative. > > > > Modules could be built without far calls by default, and then the module > > linker would only have to redirect those calls whose destination is too > > far away to a dynamically created trampoline table. > > > > If I remember correctly you even posted some patches to that effect a > > couple years ago. Maybe those could be salvaged? > > I don't think I ever did, because its pretty much impossible to do as I > explained in a follow up to this thread. > > We _used_ to do this with the userspace insmod methods, but since we got > this kernel-side linker, it's been pretty much impossible to do without > rewriting the module code. That's not going to happen on account of one > quirky architecture which Linus doesn't particularly like. Still... We could try adding a hook in the generic module linker code for a pre-relocation pass. Maybe only ARM would use it, but if the need to load big modules is real then I imagine Linus could be amenable to a compromise. Nicolas -- 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/