Re: [PATCH -tip] x86: trampoline_64.S - use predefined constants with simplification

Alexander van Heukelum
2009-01-28T22:06:28Z

On Wed, 28 Jan 2009 23:21:25 +0300, "Cyrill Gorcunov"
<gorcunov@gmail.com> said:
> Impact: cleanup
>
> We may use macros from processor-flags.h instead
> of hardcoding bits. Actually it's not direct mapping
> of old instructions with new ones -- BTS does change
> CF flag while MOV does not. But i didn't find any
> dependency on CF in this code.
>
> Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
> ---
>
> Please review

Looks good.

Acked-by: Alexander van Heukelum <heukelum@fastmail.fm>

> arch/x86/kernel/trampoline_64.S | 19 +++++++++----------
> 1 file changed, 9 insertions(+), 10 deletions(-)
>
> Index: linux-2.6.git/arch/x86/kernel/trampoline_64.S
> ===================================================================
> --- linux-2.6.git.orig/arch/x86/kernel/trampoline_64.S
> +++ linux-2.6.git/arch/x86/kernel/trampoline_64.S
> @@ -29,6 +29,7 @@
> #include <asm/page.h>
> #include <asm/msr.h>
> #include <asm/segment.h>
> +#include <asm/processor-flags.h>
>
> .section .rodata, "a", @progbits
>
> @@ -37,7 +38,7 @@
> ENTRY(trampoline_data)
> r_base = .
> cli # We should be safe anyway
> - wbinvd
> + wbinvd
> mov %cs, %ax # Code and data in the same place
> mov %ax, %ds
> mov %ax, %es
> @@ -73,9 +74,8 @@ r_base = .
> lidtl tidt - r_base # load idt with 0, 0
> lgdtl tgdt - r_base # load gdt with whatever is appropriate
>
> - xor %ax, %ax
> - inc %ax # protected mode (PE) bit
> - lmsw %ax # into protected mode
> + mov $X86_CR0_PE, %ax # protected mode (PE) bit
> + lmsw %ax # into protected mode
>
> # flush prefetch and jump to startup_32
> ljmpl *(startup_32_vector - r_base)
> @@ -86,9 +86,8 @@ startup_32:
> movl $__KERNEL_DS, %eax # Initialize the %ds segment register
> movl %eax, %ds
>
> - xorl %eax, %eax
> - btsl $5, %eax # Enable PAE mode
> - movl %eax, %cr4
> + movl $X86_CR4_PAE, %eax
> + movl %eax, %cr4 # Enable PAE mode
>
> # Setup trampoline 4 level pagetables
> leal (trampoline_level4_pgt - r_base)(%esi), %eax
> @@ -99,9 +98,9 @@ startup_32:
> xorl %edx, %edx
> wrmsr
>
> - xorl %eax, %eax
> - btsl $31, %eax # Enable paging and in turn activate Long Mode
> - btsl $0, %eax # Enable protected mode
> + # Enable paging and in turn activate Long Mode
> + # Enable protected mode
> + movl $(X86_CR0_PG | X86_CR0_PE), %eax
> movl %eax, %cr0
>
> /*
--
Alexander van Heukelum
heukelum@fastmail.fm

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