linux-kernel - Re: [PATCH v3] arm64: add ARM64-specific support for flatmem

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Date:   Tue, 10 Jul 2018 14:55:41 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Nikunj Kela <nkela@...co.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        xe-kernel@...ernal.cisco.com,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v3] arm64: add ARM64-specific support for flatmem

On Fri, Jul 6, 2018 at 7:47 PM, Nikunj Kela <nkela@...co.com> wrote:
> Flatmem is useful in reducing kernel memory usage.
> One usecase is in kdump kernel. We are able to save
> ~14M by moving to flatmem scheme.
>
> Cc: xe-kernel@...ernal.cisco.com
> Cc: Nikunj Kela <nkela@...co.com>
> Signed-off-by: Nikunj Kela <nkela@...co.com>
> ---
>  arch/arm64/Kconfig | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 42c090c..f5b4c49 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -775,6 +775,9 @@ config ARCH_SPARSEMEM_DEFAULT
>  config ARCH_SELECT_MEMORY_MODEL
>         def_bool ARCH_SPARSEMEM_ENABLE
>
> +config ARCH_FLATMEM_ENABLE
> +       def_bool y
> +
>  config HAVE_ARCH_PFN_VALID
>         def_bool ARCH_HAS_HOLES_MEMORYMODEL || !SPARSEMEM
>

I'm getting hundreds of errors in randconfig builds with this:


+ /home/arnd/cross/x86_64/gcc-8.1.0-nolibc/aarch64-linux/bin/aarch64-linux-ld
-EB -maarch64elfb --no-undefined -X -pie -shared -Bsymbolic
--no-apply-dynamic-relocs --build-id -o .tmp_vmlinux1 -T
./arch/arm64/kernel/vmlinux.lds --whole-archive built-in.a
--no-whole-archive --start-group arch/arm64/lib/lib.a lib/lib.a
--end-group
init/do_mounts.o: In function `mount_block_root':
do_mounts.c:(.init.text+0x1e8): undefined reference to `mem_map'
/home/arnd/cross/x86_64/gcc-8.1.0-nolibc/aarch64-linux/bin/aarch64-linux-ld:
init/do_mounts.o: relocation R_AARCH64_ADR_PREL_PG_HI21 against symbol
`mem_map' which may bind externally can not be used when making a
shared object; recompile with -fPIC
do_mounts.c:(.init.text+0x1e8): dangerous relocation: unsupported relocation
do_mounts.c:(.init.text+0x1f4): undefined reference to `mem_map'
arch/arm64/kernel/vdso.o: In function `vdso_init':
vdso.c:(.init.text+0xb4): undefined reference to `mem_map'
/home/arnd/cross/x86_64/gcc-8.1.0-nolibc/aarch64-linux/bin/aarch64-linux-ld:
arch/arm64/kernel/vdso.o: relocation R_AARCH64_ADR_PREL_PG_HI21
against symbol `mem_map' which may bind externally can not be used
when making a shared object; recompile with -fPIC
vdso.c:(.init.text+0xb4): dangerous relocation: unsupported relocation
vdso.c:(.init.text+0xbc): undefined reference to `mem_map'
vdso.c:(.init.text+0xec): undefined reference to `mem_map'
arch/arm64/kernel/insn.o:insn.c:(.text+0x2ec): more undefined
references to `mem_map' follow
/home/arnd/cross/x86_64/gcc-8.1.0-nolibc/aarch64-linux/bin/aarch64-linux-ld:
arch/arm64/kernel/insn.o: relocation R_AARCH64_ADR_PREL_PG_HI21
against symbol `mem_map' which may bind externally can not be used
when making a shared object; recompile with -fPIC

The problem seems to be that CONFIG_NUMA is enabled in my
build, so mem_map[] is not defined anywhere.

     Arnd