kernel header解析

一、kernel header定义： 

======aarch64 kernel header========
u32 code0;          /* Executable code */
u32 code1;          /* Executable code */
u64 text_offset;        /* Image load offset, little endian */
u64 image_size;     /* Effective Image size, little endian */
u64 flags;          /* kernel flags, little endian */
u64 res2    = 0;        /* reserved */
u64 res3    = 0;        /* reserved */
u64 res4    = 0;        /* reserved */
u32 magic   = 0x644d5241;   /* Magic number, little endian, "ARM\x64" */
u32 res5;           /* reserved (used for PE COFF offset) */
====================================

//TEXT_OFFSET是kernel镜像在内存中的偏移量。

注意事项： 

Header notes:

• As of v3.17, all fields are little endian unless stated otherwise.

• code0/code1 are responsible for branching to stext.

• when booting through EFI, code0/code1 are initially skipped. res5 is an offset to the PE header and the PE header has the EFI entry point (efi_stub_entry). When the stub has done its work, it jumps to code0 to resume the normal boot process.

• Prior to v3.17, the endianness of text_offset was not specified. In these cases image_size is zero and text_offset is 0x80000 in the endianness of the kernel. Where image_size is non-zero image_size is little-endian and must be respected. Where image_size is zero, text_offset can be assumed to be 0x80000.

• The flags field (introduced in v3.17) is a little-endian 64-bit field composed as follows:

  Bit 0	Kernel endianness. 1 if BE, 0 if LE.
  Bit 1-2	Kernel Page size. 0 - Unspecified. 1 - 4K 2 - 16K 3 - 64K
  Bit 3	Kernel physical placement 0 2MB aligned base should be as close as possible to the base of DRAM, since memory below it is not accessible via the linear mapping 1 2MB aligned base may be anywhere in physical memory
  Bits 4-63	Reserved.

 参考：https://github.com/torvalds/linux/blob/ff1176468d368232b684f75e82563369208bc371/Documentation/arm64/booting.rst