Messages in this thread | | | Date | Wed, 19 Nov 2014 11:37:47 -0500 (EST) | From | Nicolas Pitre <> | Subject | Re: [PATCH RFC] ARM: option for loading modules into vmalloc area |
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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 <koct9i@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.
Nicolas
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