linux-kernel - Re: [PATCH 2/4] x86/boot: replace __PHYSICAL_START with LOAD_PHYSICAL

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Date: Thu, 14 Mar 2024 03:23:20 +0000
From: Wei Yang <richard.weiyang@...il.com>
To: Ingo Molnar <mingo@...nel.org>
Cc: Wei Yang <richard.weiyang@...il.com>, tglx@...utronix.de,
	mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
	x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] x86/boot: replace __PHYSICAL_START with
 LOAD_PHYSICAL_ADDR

On Wed, Mar 13, 2024 at 11:29:33AM +0100, Ingo Molnar wrote:
>
>* Wei Yang <richard.weiyang@...il.com> wrote:
>
>> Both __PHYSICAL_START and LOAD_PHYSICAL_ADDR are defined to get aligned
>> CONFIG_PHYSICAL_START, so we can replace __PHYSICAL_START with
>> LOAD_PHYSICAL_ADDR. And then remove the definition of __PHYSICAL_START,
>> which is only used to define __START_KERNEL.
>> 
>> Since <asm/boot.h> includes <asm/pgtable_types.h>, which includes
>> <asm/page_types.h>, it is fine to move definition from <asm/boot.h> to
>> <asm/page_types.h>.
>> 
>> Signed-off-by: Wei Yang <richard.weiyang@...il.com>
>> ---
>>  arch/x86/include/asm/boot.h       | 5 -----
>>  arch/x86/include/asm/page_types.h | 8 +++++---
>>  2 files changed, 5 insertions(+), 8 deletions(-)
>> 
>> diff --git a/arch/x86/include/asm/boot.h b/arch/x86/include/asm/boot.h
>> index a38cc0afc90a..12cbc57d0128 100644
>> --- a/arch/x86/include/asm/boot.h
>> +++ b/arch/x86/include/asm/boot.h
>> @@ -6,11 +6,6 @@
>>  #include <asm/pgtable_types.h>
>>  #include <uapi/asm/boot.h>
>>  
>> -/* Physical address where kernel should be loaded. */
>> -#define LOAD_PHYSICAL_ADDR ((CONFIG_PHYSICAL_START \
>> -				+ (CONFIG_PHYSICAL_ALIGN - 1)) \
>> -				& ~(CONFIG_PHYSICAL_ALIGN - 1))
>> -
>>  /* Minimum kernel alignment, as a power of two */
>>  #ifdef CONFIG_X86_64
>>  # define MIN_KERNEL_ALIGN_LG2	PMD_SHIFT
>> diff --git a/arch/x86/include/asm/page_types.h b/arch/x86/include/asm/page_types.h
>> index 86bd4311daf8..acc1620fd121 100644
>> --- a/arch/x86/include/asm/page_types.h
>> +++ b/arch/x86/include/asm/page_types.h
>> @@ -31,10 +31,12 @@
>>  
>>  #define VM_DATA_DEFAULT_FLAGS	VM_DATA_FLAGS_TSK_EXEC
>>  
>> -#define __PHYSICAL_START	ALIGN(CONFIG_PHYSICAL_START, \
>> -				      CONFIG_PHYSICAL_ALIGN)
>> +/* Physical address where kernel should be loaded. */
>> +#define LOAD_PHYSICAL_ADDR ((CONFIG_PHYSICAL_START \
>> +				+ (CONFIG_PHYSICAL_ALIGN - 1)) \
>> +				& ~(CONFIG_PHYSICAL_ALIGN - 1))
>
>I agree with this simplification, but the ALIGN() expression is far easier 
>to read, so please keep that one instead of the open-coded version.
>

I just tried to define LOAD_PHYSICAL_ADDR by ALIGN, but face a compile error
on compressed/head_[32|64].o.

$ make arch/x86/boot/compressed/head_64.o
  CALL    scripts/checksyscalls.sh
  DESCEND objtool
  INSTALL libsubcmd_headers
  AS      arch/x86/boot/compressed/head_64.o
arch/x86/boot/compressed/head_64.S: Assembler messages:
arch/x86/boot/compressed/head_64.S:154: Error: junk (0x1000000,0x200000)' after expression
arch/x86/boot/compressed/head_64.S:154: Error: number of operands mismatch for 16' after expression
arch/x86/boot/compressed/head_64.S:157: Error: junk mov'
arch/x86/boot/compressed/head_64.S:330: Error: junk (0x1000000,0x200000)' after expression
arch/x86/boot/compressed/head_64.S:330: Error: number of operands mismatch for 16' after expression
arch/x86/boot/compressed/head_64.S:333: Error: junk movq'

If my understanding is correct, the reason is linkage.h defines ALIGN, which
is ".balign xxx". Maybe this is why original LOAD_PHYSICAL_ADDR doesn't use
ALIGN.

So is this ok to keep the open-coded definition?

>Thanks,
>
>	Ingo

-- 
Wei Yang
Help you, Help me