On 19 November 2014 17:37, Nicolas Pitre <nicolas.pi...@linaro.org> wrote: > On Wed, 19 Nov 2014, Russell King - ARM Linux wrote: > >> On Wed, Nov 19, 2014 at 05:02:40PM +0100, Ard Biesheuvel wrote: >> > On 19 November 2014 16:52, Konstantin Khlebnikov <koc...@gmail.com> wrote: >> > > 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: >> >> 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 would largely recommend a solution where the link process could deal > with it automatically and as needed rather than sprinkling yet more > manually maintained macros into assembly code. >
Yes, that would be preferable. I played around with 'bl symbol@PLT' instead of plain 'bl symbol' but unfortunately, our .ko's are not proper ELF shared libraries, so that doesn't work. But essentially, we just need a (eager) PLT. -- Ard. -- 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/