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SubjectRe: [PATCH 17/20] x86_64: Remove CONFIG_PHYSICAL_START
Hi Vivek,

Sorry for not commenting on an earlier version.

On 11/18/06, Vivek Goyal <vgoyal@in.ibm.com> wrote:
> I am about to add relocatable kernel support which has essentially
> no cost so there is no point in retaining CONFIG_PHYSICAL_START
> and retaining CONFIG_PHYSICAL_START makes implementation of and
> testing of a relocatable kernel more difficult.
>
> Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
> Signed-off-by: Vivek Goyal <vgoyal@in.ibm.com>
> ---
>
> arch/x86_64/Kconfig | 19 -------------------
> arch/x86_64/boot/compressed/head.S | 6 +++---
> arch/x86_64/boot/compressed/misc.c | 6 +++---
> arch/x86_64/defconfig | 1 -
> arch/x86_64/kernel/vmlinux.lds.S | 2 +-
> arch/x86_64/mm/fault.c | 4 ++--
> include/asm-x86_64/page.h | 2 --
> 7 files changed, 9 insertions(+), 31 deletions(-)

[snip]

> diff -puN arch/x86_64/mm/fault.c~x86_64-Remove-CONFIG_PHYSICAL_START arch/x86_64/mm/fault.c
> --- linux-2.6.19-rc6-reloc/arch/x86_64/mm/fault.c~x86_64-Remove-CONFIG_PHYSICAL_START 2006-11-17 00:12:50.000000000 -0500
> +++ linux-2.6.19-rc6-reloc-root/arch/x86_64/mm/fault.c 2006-11-17 00:12:50.000000000 -0500
> @@ -644,9 +644,9 @@ void vmalloc_sync_all(void)
> start = address + PGDIR_SIZE;
> }
> /* Check that there is no need to do the same for the modules area. */
> - BUILD_BUG_ON(!(MODULES_VADDR > __START_KERNEL));
> + BUILD_BUG_ON(!(MODULES_VADDR > __START_KERNEL_map));
> BUILD_BUG_ON(!(((MODULES_END - 1) & PGDIR_MASK) ==
> - (__START_KERNEL & PGDIR_MASK)));
> + (__START_KERNEL_map & PGDIR_MASK)));
> }

This code looks either like a bugfix or a bug. If it's a fix then
maybe it should be broken out and submitted separately for the
rc-kernels?

> diff -puN include/asm-x86_64/page.h~x86_64-Remove-CONFIG_PHYSICAL_START include/asm-x86_64/page.h
> --- linux-2.6.19-rc6-reloc/include/asm-x86_64/page.h~x86_64-Remove-CONFIG_PHYSICAL_START 2006-11-17 00:12:50.000000000 -0500
> +++ linux-2.6.19-rc6-reloc-root/include/asm-x86_64/page.h 2006-11-17 00:12:50.000000000 -0500
> @@ -75,8 +75,6 @@ typedef struct { unsigned long pgprot; }
>
> #endif /* !__ASSEMBLY__ */
>
> -#define __PHYSICAL_START _AC(CONFIG_PHYSICAL_START,UL)
> -#define __START_KERNEL (__START_KERNEL_map + __PHYSICAL_START)
> #define __START_KERNEL_map _AC(0xffffffff80000000,UL)
> #define __PAGE_OFFSET _AC(0xffff810000000000,UL)

I understand that you want to remove the Kconfig option
CONFIG_PHYSICAL_START and that is fine with me. I don't however like
the idea of replacing __PHYSICAL_START and __START_KERNEL with
hardcoded values. Is there any special reason behind this?

The code in page.h already has constants for __START_KERNEL_map and
__PAGE_OFFSET (thank god) and none of them are adjustable via Kconfig.
Why not change as little as possible and keep __PHYSICAL_START and
__START_KERNEL in page.h and the places that use them but remove
references to CONFIG_PHYSICAL_START in Kconfig, defconfig, and page.h?

/ magnus
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