On Wed, 19 Nov 2014, Ard Biesheuvel wrote: > On 19 November 2014 18:12, Nicolas Pitre <nicolas.pi...@linaro.org> wrote: > > On Wed, 19 Nov 2014, Russell King - ARM Linux wrote: > > > >> On Wed, Nov 19, 2014 at 11:57:15AM -0500, Nicolas Pitre wrote: > >> > On Wed, 19 Nov 2014, Russell King - ARM Linux wrote: > >> > > 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. > >> > >> So, how big a table would you allocate for the trampolines, based upon > >> not knowing anything about the module being loaded? 4K? 8K? 64K? > > > > The idea of a pre-relocation pass is to determine that. That could be > > something similar to calling apply_relocate() twice: once to determine > > the number of trampoline entries, and a second time to perform the > > actual relocation. > > > > Well, the veneers shouldn't take more than 3 words each, right? > > ldr ip, [pc] > bx ip > .long symbol
You could possibly do: ldr pc, [pc, #-4] .long symbol Or, as RMK suggested a while ago: .rep 8 ldr pc, [pc, #(32 - 8)] .endr .long sym1, sym2, sym3, sym4, sym5, sym6, sym7, sym8 The later is much nicer on the i and d caches. > and you would need at most one veneer per unique external symbol > referenced by one or more R_ARM_CALL relocations. Is there no way to > just add that to the static mem footprint as padding, and let the > loader populate it as needed at module relocation time? That's the actual question: how much padding do you need? Everything converge to that very problem. We need to determine it without too much impact on the generic module loader code. Nicolas -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
