From mboxrd@z Thu Jan 1 00:00:00 1970 From: nicolas.pitre@linaro.org (Nicolas Pitre) Date: Wed, 19 Nov 2014 11:57:15 -0500 (EST) Subject: [PATCH RFC] ARM: option for loading modules into vmalloc area In-Reply-To: <20141119164902.GK4042@n2100.arm.linux.org.uk> 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> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.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