Re: [PATCH RFC] ARM: option for loading modules into vmalloc area
From: Russell King - ARM Linux
Date: Tue Nov 18 2014 - 12:41:56 EST
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
> diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
> index 9d2cdda..9e0c4f4 100644
> --- a/arch/arm/mm/mmu.c
> +++ b/arch/arm/mm/mmu.c
> @@ -1161,16 +1161,15 @@ void __init sanity_check_meminfo(void)
> static inline void prepare_page_table(void)
> - unsigned long addr;
> + unsigned long addr = 0;
> phys_addr_t end;
> * Clear out all the mappings below the kernel image.
> - for (addr = 0; addr < MODULES_VADDR; addr += PMD_SIZE)
> - pmd_clear(pmd_off_k(addr));
> #ifdef CONFIG_XIP_KERNEL
> + for ( ; addr < MODULES_VADDR; addr += PMD_SIZE)
> + pmd_clear(pmd_off_k(addr));
> /* The XIP kernel is mapped in the module area -- skip over it */
> addr = ((unsigned long)_etext + PMD_SIZE - 1) & PMD_MASK;
This seems to be an unrelated change. In any case, it looks wrong to
me. Please describe what you are trying to achieve here.
FTTC broadband for 0.8mile line: currently at 9.5Mbps down 400kbps up
according to speedtest.net.
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