linux-kernel - Re: [PATCH 4.9 62/88] x86/boot/compressed: Dont declare __force_order in kaslr

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Date:   Tue, 10 Mar 2020 15:33:57 +0100 (CET)
From:   Thomas Voegtle <tv@...96.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        "H.J. Lu" <hjl.tools@...il.com>, Borislav Petkov <bp@...e.de>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 4.9 62/88] x86/boot/compressed: Dont declare __force_order
 in kaslr_64.c

On Tue, 10 Mar 2020, Greg Kroah-Hartman wrote:

> From: H.J. Lu <hjl.tools@...il.com>
>
> [ Upstream commit df6d4f9db79c1a5d6f48b59db35ccd1e9ff9adfc ]
>
> GCC 10 changed the default to -fno-common, which leads to
>
>    LD      arch/x86/boot/compressed/vmlinux
>  ld: arch/x86/boot/compressed/pgtable_64.o:(.bss+0x0): multiple definition of `__force_order'; \
>    arch/x86/boot/compressed/kaslr_64.o:(.bss+0x0): first defined here
>  make[2]: *** [arch/x86/boot/compressed/Makefile:119: arch/x86/boot/compressed/vmlinux] Error 1
>
> Since __force_order is already provided in pgtable_64.c, there is no
> need to declare __force_order in kaslr_64.c.
>
> Signed-off-by: H.J. Lu <hjl.tools@...il.com>
> Signed-off-by: Borislav Petkov <bp@...e.de>
> Link: https://lkml.kernel.org/r/20200124181811.4780-1-hjl.tools@gmail.com
> Signed-off-by: Sasha Levin <sashal@...nel.org>
> ---
> arch/x86/boot/compressed/pagetable.c | 3 ---
> 1 file changed, 3 deletions(-)
>
> diff --git a/arch/x86/boot/compressed/pagetable.c b/arch/x86/boot/compressed/pagetable.c
> index 56589d0a804b1..2591f8f6d45f2 100644
> --- a/arch/x86/boot/compressed/pagetable.c
> +++ b/arch/x86/boot/compressed/pagetable.c
> @@ -25,9 +25,6 @@
> #define __PAGE_OFFSET __PAGE_OFFSET_BASE
> #include "../../mm/ident_map.c"
>
> -/* Used by pgtable.h asm code to force instruction serialization. */
> -unsigned long __force_order;
> -
> /* Used to track our page table allocation area. */
> struct alloc_pgt_data {
> 	unsigned char *pgt_buf;
>


This ends up for me in:

arch/x86/boot/compressed/pagetable.o: In function 
`initialize_identity_maps':
pagetable.c:(.text+0x309): undefined reference to `__force_order'
arch/x86/boot/compressed/pagetable.o: In function 
`finalize_identity_maps':
pagetable.c:(.text+0x41a): undefined reference to `__force_order'


pgtable_64.c doesn't exist in v4.9 for x86.

So I guess it's not correct to remove __force_order from pagetable.c?


    Thomas