Re: [PATCH v1 1/2] docs/LoongArch: Add boot image header

[Wu XiangCheng <wu.xiangcheng@linux.dev>]

+Cc: Yun Liu <liuyun@loongson.cn>

2022-11-21 (一) 20:16:30 +0800 Yanteng Si 曰：
> Describes the meaning and value of the image header field.
> 
> Suggested-by: Xiaotian Wu <wuxiaotian@loongson.cn>
> Signed-off-by: Yanteng Si <siyanteng@loongson.cn>
> ---
>  Documentation/loongarch/boot-image-header.rst | 76 +++++++++++++++++++
>  Documentation/loongarch/index.rst             |  1 +
>  2 files changed, 77 insertions(+)
>  create mode 100644 Documentation/loongarch/boot-image-header.rst
> 
> diff --git a/Documentation/loongarch/boot-image-header.rst b/Documentation/loongarch/boot-image-header.rst
> new file mode 100644
> index 000000000000..92a953a6f2e6
> --- /dev/null
> +++ b/Documentation/loongarch/boot-image-header.rst
> @@ -0,0 +1,76 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +====================================
> +Boot image header in LoongArch Linux
> +====================================
> +
> +:Author: Yanteng Si <siyanteng@loongson.cn>
> +:Date:   18 Nov 2022
> +
> +This document only describes the boot image header details for
> +LoongArch Linux.
> +
> +The following 64-byte header is present in decompressed Linux
> +kernel image::
> +
> +	u32	MZ_MAGIC		/* "MZ", MS-DOS header */
> +	u32	res0 = 0		/* reserved */
> +	u64	kernel_entry		/* Kernel entry point */
> +	u64	_end - _text		/* Kernel image effective size */
> +	u64	0			/* Kernel image load offset from start of RAM */
> +	u64	res1 = 0		/* reserved */
> +	u64	res2 = 0		/* reserved */
> +	u64	res3 = 0		/* reserved */
> +	u32	res4 = 0		/* reserved */
> +	u32	pe_header - _head	/* Offset to the PE header */
> +

Any code related need to be linked here?

> +
> +Header notes
> +============
> +
> +Currently, LoongArch has removed the "magic" field.
> +
> +According to the EFI specification, the PE/COFF image file header is
> +required at the beginning of the kernel image; the LoongArch kernel
> +supports the EFI stub, so the first two bytes of the kernel image header
> +are "MZ" magic characters, and 0x3c should point to the rest of the
> +PE/COFF file header, between which The kernel entry point, image
> +effectivesize, and image load offset layout are as follows::
> +
> +          +-----------------------------------------------+
> +    0x0:  |  0  |  1  |  2  |  3  |  4  |  5  |  6  |  7  |
> +          +-----------------------------------------------+
> +    0x8:  | MZ_MAGIC              |          res0         |
> +          +-----------------------------------------------+
> +    0x10: |                 kernel_entry                  |
> +          +-----------------------------------------------+
> +    0x18: |                  _end - _text                 |
> +          +-----------------------------------------------+
> +    0x20: |                       0                       |
> +          +-----------------------------------------------+
> +    0x28: |                      res1                     |
> +          +-----------------------------------------------+
> +    0x30: |                      res2                     |
> +          +-----------------------------------------------+
> +    0x38: |                      res3                     |
> +          +-----------------------------------------------+
> +    0x40: |          res14        |       PE header       |
> +          +-----------------------------------------------+
> +

emmm, this figure...

So MZ_MAGIC start from 0x08 ?

Or

            0     1     2     3     4     5     6     7   
         +-----------------------+-----------------------+
    0x00 |        MZ_MAGIC       |          res0         |
         +-----------------------+-----------------------+
    0x08 |                 kernel_entry                  |
         +-----------------------------------------------+
    0x10 |                  _end - _text                 |
         +-----------------------------------------------+
    0x18 |                       0                       |
         +-----------------------------------------------+
    0x20 |                      res1                     |
         +-----------------------------------------------+
    0x28 |                      res2                     |
         +-----------------------------------------------+
    0x30 |                      res3                     |
         +-----------------------+-----------------------+
    0x38 |          res14        |       PE header       |
         +-----------------------+-----------------------+

If the figure is too difficult to draw, a simple table can also be used
to instead.

Offset	Name	Size	Note
...

> +
> +All bit fields are in little endian:
> +
> +    - MZ: Effective length of 2 bytes;
> +
> +    - kernel entry point: leaving 6 bytes blank in front, starting
> +      from 0x8, with a effective length of 8 bytes;
> +
> +    - kernel image effective size: Immediately following the kernel
> +      entry point, with a effective length of 8 bytes, this field is
> +      required for the bootloader;
> +
> +    - kernel image load offset: Immediately following the kernel
> +      image effective size, with a effective length of 8 bytes;
> +
> +    - Offset to the PE header: leaving 28 bytes blank in front,
> +      starting from 0x3c, with a effective length of 4 bytes.
> diff --git a/Documentation/loongarch/index.rst b/Documentation/loongarch/index.rst
> index aaba648db907..97419821adf9 100644
> --- a/Documentation/loongarch/index.rst
> +++ b/Documentation/loongarch/index.rst
> @@ -10,6 +10,7 @@ LoongArch Architecture
>  
>     introduction
>     irq-chip-model
> +   boot-image-header
>  
>     features
>  
> -- 
> 2.31.1
> 

-- 
Wu XiangCheng	0x32684A40BCA7AEA7