Messages in this thread | | | Date | Wed, 19 Nov 2014 19:52:39 +0400 | Subject | Re: [PATCH RFC] ARM: option for loading modules into vmalloc area | From | Konstantin Khlebnikov <> |
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On Wed, Nov 19, 2014 at 5:54 PM, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote: > On 19 November 2014 14:40, Arnd Bergmann <arnd@arndb.de> wrote: >> On Tuesday 18 November 2014 21:13:56 Konstantin Khlebnikov wrote: >>> On 2014-11-18 20:34, Russell King - ARM Linux wrote: >>> > On Tue, Nov 18, 2014 at 08:21:46PM +0400, Konstantin Khlebnikov wrote: >>> >> Usually modules are loaded into small area prior to the kernel >>> >> text because they are linked with the kernel using short calls. >>> >> Compile-time instrumentation like GCOV or KASAN bloats code a lot, >>> >> and as a result huge modules no longer fit into reserved area. >>> >> >>> >> This patch adds option CONFIG_MODULES_USE_VMALLOC which lifts >>> >> limitation on amount of loaded modules. It links modules using >>> >> long-calls (option -mlong-calls) and loads them into vmalloc area. >>> >> >>> >> In few places exported symbols are called from inline assembly. >>> >> This patch adds macro for such call sites: __asmbl and __asmbl_clobber. >>> >> Call turns into single 'bl' or sequence 'movw; movt; blx' depending on >>> >> context and state of config option. >>> >> >>> >> Unfortunately this option isn't compatible with CONFIG_FUNCTION_TRACER. >>> >> Compiler emits short calls to profiling function despite of -mlong-calls. >>> >> This is a bug in GCC, but ftrace anyway needs an update to handle this. >>> > It also isn't compatible with the older architectures which don't have >>> > "blx". >>> >>> Ok, I'll add "depends on CPU_V6 || CPU_V7" I don't think that it is >>> necessary for older cpus. >> >> Why not just use a different branch instruction for the older CPUs? >> > > ARMv6 doesn't support movw/movt so this will only work on v7. > > What about doing 'mov lr, pc; ldr pc,=symbol' instead? You clearly > don't care about performance in this case, so the performance hit (due > to the dcache access and interfering with the return stack predictors) > should be tolerable. The only thing to be careful about is thumb2 > kernels: you would need to set the thumb bit in lr manually but only > if the call is made /from/ thumb. You would probably be better off > just depending on !THUMB2_KERNEL.
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
> Ard. > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
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