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Date: Fri, 15 Mar 2024 00:57:37 +0000
From: Wei Yang <richard.weiyang@gmail.com>
To: Ingo Molnar <mingo@kernel.org>
Cc: Wei Yang <richard.weiyang@gmail.com>, tglx@linutronix.de,
	mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com,
	x86@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/4] x86/boot: replace __PHYSICAL_START with
 LOAD_PHYSICAL_ADDR
Message-ID: <20240315005737.yxisrooskigl4zef@master>
Reply-To: Wei Yang <richard.weiyang@gmail.com>
References: <20240313075839.8321-1-richard.weiyang@gmail.com>
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 <20240314032320.iug2hvzyblychanu@master>
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On Thu, Mar 14, 2024 at 10:25:53AM +0100, Ingo Molnar wrote:
>
>* Wei Yang <richard.weiyang@gmail.com> wrote:
>
>> On Wed, Mar 13, 2024 at 11:29:33AM +0100, Ingo Molnar wrote:
>> >
>> >* Wei Yang <richard.weiyang@gmail.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@gmail.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.
>
>linkage.h defines __ALIGN, which is different from ALIGN().
>

linkage.h defines ALIGN to __ALIGN which is different from what we expect.

>Also, a number of .S files seem to be using some sort of ALIGN() method 
>within arch/x86/, according to:
>
>   git grep 'ALIGN(' -- 'arch/x86/*.S'

I tried below command by append '\<' to ALIGN 

    git grep '\<ALIGN(' -- 'arch/x86/*.S'

>
>> So is this ok to keep the open-coded definition?
>
>It would be nice to figure out why ALIGN() appears to be working in other 
>cases in .S files, while not in this case.
>

Here is grep result

arch/x86/boot/compressed/vmlinux.lds.S:	.data :	ALIGN(0x1000) {
arch/x86/boot/compressed/vmlinux.lds.S:		. = ALIGN(. + 4, 0x200);
arch/x86/boot/compressed/vmlinux.lds.S:	. = ALIGN(L1_CACHE_BYTES);
arch/x86/boot/compressed/vmlinux.lds.S:		. = ALIGN(8);	/* For convenience during zeroing */
arch/x86/boot/compressed/vmlinux.lds.S:       . = ALIGN(PAGE_SIZE);
arch/x86/boot/compressed/vmlinux.lds.S:	. = ALIGN(PAGE_SIZE);	/* keep ZO size page aligned */
arch/x86/kernel/vmlinux.lds.S:#define X86_ALIGN_RODATA_BEGIN	. = ALIGN(HPAGE_SIZE);
arch/x86/kernel/vmlinux.lds.S:		. = ALIGN(HPAGE_SIZE);				\
arch/x86/kernel/vmlinux.lds.S:#define ALIGN_ENTRY_TEXT_BEGIN	. = ALIGN(PMD_SIZE);
arch/x86/kernel/vmlinux.lds.S:#define ALIGN_ENTRY_TEXT_END	. = ALIGN(PMD_SIZE);
arch/x86/kernel/vmlinux.lds.S:	. = ALIGN(PMD_SIZE);					\
arch/x86/kernel/vmlinux.lds.S:	. = ALIGN(PAGE_SIZE);					\
arch/x86/kernel/vmlinux.lds.S:	. = ALIGN(PMD_SIZE);					\
arch/x86/kernel/vmlinux.lds.S:		. = ALIGN(PAGE_SIZE);				\
arch/x86/kernel/vmlinux.lds.S:	. = ALIGN(PAGE_SIZE);
arch/x86/kernel/vmlinux.lds.S:	. = ALIGN(PAGE_SIZE);
arch/x86/kernel/vmlinux.lds.S:	. = ALIGN(__vvar_page + PAGE_SIZE, PAGE_SIZE);
arch/x86/kernel/vmlinux.lds.S:	. = ALIGN(PAGE_SIZE);
arch/x86/kernel/vmlinux.lds.S:	. = ALIGN(8);
arch/x86/kernel/vmlinux.lds.S:	. = ALIGN(8);
arch/x86/kernel/vmlinux.lds.S:	. = ALIGN(8);
arch/x86/kernel/vmlinux.lds.S:	. = ALIGN(8);
arch/x86/kernel/vmlinux.lds.S:	. = ALIGN(8);
arch/x86/kernel/vmlinux.lds.S:	. = ALIGN(8);
arch/x86/kernel/vmlinux.lds.S:	. = ALIGN(8);
arch/x86/kernel/vmlinux.lds.S:	. = ALIGN(8);
arch/x86/kernel/vmlinux.lds.S:	. = ALIGN(PAGE_SIZE);
arch/x86/kernel/vmlinux.lds.S:	. = ALIGN(PAGE_SIZE);
arch/x86/kernel/vmlinux.lds.S:		. = ALIGN(PAGE_SIZE);
arch/x86/kernel/vmlinux.lds.S:	. = ALIGN(PAGE_SIZE);
arch/x86/kernel/vmlinux.lds.S:		. = ALIGN(PAGE_SIZE);
arch/x86/kernel/vmlinux.lds.S:		. = ALIGN(PAGE_SIZE);
arch/x86/kernel/vmlinux.lds.S:	. = ALIGN(PAGE_SIZE);
arch/x86/kernel/vmlinux.lds.S:	. = ALIGN(PAGE_SIZE);		/* keep VO_INIT_SIZE page aligned */
arch/x86/kernel/vmlinux.lds.S:	. = ALIGN(HPAGE_SIZE);
arch/x86/kernel/vmlinux.lds.S:		. = ALIGN(HPAGE_SIZE);
arch/x86/realmode/rm/realmode.lds.S:	. = ALIGN(4);
arch/x86/realmode/rm/realmode.lds.S:		. = ALIGN(16);
arch/x86/realmode/rm/realmode.lds.S:	. = ALIGN(PAGE_SIZE);
arch/x86/realmode/rm/realmode.lds.S:	. = ALIGN(PAGE_SIZE);
arch/x86/realmode/rm/realmode.lds.S:	. = ALIGN(128);
arch/x86/realmode/rm/realmode.lds.S:	. = ALIGN(4);
arch/x86/um/vdso/vdso-layout.lds.S:	. = ALIGN(0x100);

It looks all happens in link script, not assembly source code.

And other grep result with "ALIGN" are:

    SYM_CODE_START_NOALIGN
    SYM_CODE_START_LOCAL_NOALIGN
    SYM_FUNC_START_NOALIGN
    SYM_FUNC_START_LOCAL_NOALIGN
    SYM_INNER_LABEL_ALIGN

which are defined in linkage.h.

>Thanks,
>
>	Ingo

-- 
Wei Yang
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