UEFI（2）：PPI和HOB列表（PEI-＞DXE）

前置步调：

• 准备UEFI实验环境教程：搭建edk2编译环境
  
• UEFI官方技术参考手册
  

HOB（Hand-Off Block）是一个通用的布局体类型：MdePkg/Include/Pi/PiHob.h

1. ///
2. /// Describes the format and size of the data inside the HOB.
3. /// All HOBs must contain this generic HOB header.
4. ///
5. typedef struct {
6.   ///
7.   /// Identifies the HOB data structure type.
8.   ///
9.   UINT16    HobType;
10.   ///
11.   /// The length in bytes of the HOB.
12.   ///
13.   UINT16    HobLength;
14.   ///
15.   /// This field must always be set to zero.
16.   ///
17.   UINT32    Reserved;
18. } EFI_HOB_GENERIC_HEADER;

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EFI_HOB_GENERIC_HEADER是所有HOB布局的通用头部，它包罗了HOB的类型、长度以及指向下一个HOB的指针
除了通用头部，具体的HOB数据布局根据HobType的差别会有差别的定义
EFI_HOB_HANDOFF_INFO_TABLE
用于描述HOB列表的起始信息，通常是第一个HOB，用于传递PEI到DXE的过渡信息：MdePkg/Include/Pi/PiHob.h

1. ///
2. /// Contains general state information used by the HOB producer phase.
3. /// This HOB must be the first one in the HOB list.
4. ///
5. typedef struct {
6.   ///
7.   /// The HOB generic header. Header.HobType = EFI_HOB_TYPE_HANDOFF.
8.   ///
9.   EFI_HOB_GENERIC_HEADER    Header;
10.   ///
11.   /// The version number pertaining to the PHIT HOB definition.
12.   /// This value is four bytes in length to provide an 8-byte aligned entry
13.   /// when it is combined with the 4-byte BootMode.
14.   ///
15.   UINT32                    Version;
16.   ///
17.   /// The system boot mode as determined during the HOB producer phase.
18.   ///
19.   EFI_BOOT_MODE             BootMode;
20.   ///
21.   /// The highest address location of memory that is allocated for use by the HOB producer
22.   /// phase. This address must be 4-KB aligned to meet page restrictions of UEFI.
23.   ///
24.   EFI_PHYSICAL_ADDRESS      EfiMemoryTop;
25.   ///
26.   /// The lowest address location of memory that is allocated for use by the HOB producer phase.
27.   ///
28.   EFI_PHYSICAL_ADDRESS      EfiMemoryBottom;
29.   ///
30.   /// The highest address location of free memory that is currently available
31.   /// for use by the HOB producer phase.
32.   ///
33.   EFI_PHYSICAL_ADDRESS      EfiFreeMemoryTop;
34.   ///
35.   /// The lowest address location of free memory that is available for use by the HOB producer phase.
36.   ///
37.   EFI_PHYSICAL_ADDRESS      EfiFreeMemoryBottom;
38.   ///
39.   /// The end of the HOB list.
40.   ///
41.   EFI_PHYSICAL_ADDRESS      EfiEndOfHobList;
42. } EFI_HOB_HANDOFF_INFO_TABLE;

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EFI_HOB_MEMORY_ALLOCATION
描述内存分配环境的HOB，用于报告已分配的内存范围：MdePkg/Include/Pi/PiHob.h

1. ///
2. /// Describes all memory ranges used during the HOB producer
3. /// phase that exist outside the HOB list. This HOB type
4. /// describes how memory is used, not the physical attributes of memory.
5. ///
6. typedef struct {
7.   ///
8.   /// The HOB generic header. Header.HobType = EFI_HOB_TYPE_MEMORY_ALLOCATION.
9.   ///
10.   EFI_HOB_GENERIC_HEADER              Header;
11.   ///
12.   /// An instance of the EFI_HOB_MEMORY_ALLOCATION_HEADER that describes the
13.   /// various attributes of the logical memory allocation.
14.   ///
15.   EFI_HOB_MEMORY_ALLOCATION_HEADER    AllocDescriptor;
16.   //
17.   // Additional data pertaining to the "Name" Guid memory
18.   // may go here.
19.   //
20. } EFI_HOB_MEMORY_ALLOCATION;

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EFI_HOB_GUID_TYPE
这是一个通用的HOB类型，用于存储自定义数据。它由GUID标识并携带特定数据

1. ///
2. /// Allows writers of executable content in the HOB producer phase to
3. /// maintain and manage HOBs with specific GUID.
4. ///
5. typedef struct {
6.   ///
7.   /// The HOB generic header. Header.HobType = EFI_HOB_TYPE_GUID_EXTENSION.
8.   ///
9.   EFI_HOB_GENERIC_HEADER    Header;
10.   ///
11.   /// A GUID that defines the contents of this HOB.
12.   ///
13.   EFI_GUID                  Name;
14.   //
15.   // Guid specific data goes here
16.   //
17. } EFI_HOB_GUID_TYPE;

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  每个HOB元素通过EFI_HOB_GENERIC_HEADER中的HobLength字段举行计算，找到下一个HOB的位置，停止HOB为EFI_HOB_TYPE_END_OF_HOB_LIST类型

1. //
2. // HobType of EFI_HOB_GENERIC_HEADER.
3. //
4. #define EFI_HOB_TYPE_HANDOFF              0x0001
5. #define EFI_HOB_TYPE_MEMORY_ALLOCATION    0x0002
6. #define EFI_HOB_TYPE_RESOURCE_DESCRIPTOR  0x0003
7. #define EFI_HOB_TYPE_GUID_EXTENSION       0x0004
8. #define EFI_HOB_TYPE_FV                   0x0005
9. #define EFI_HOB_TYPE_CPU                  0x0006
10. #define EFI_HOB_TYPE_MEMORY_POOL          0x0007
11. #define EFI_HOB_TYPE_FV2                  0x0009
12. #define EFI_HOB_TYPE_LOAD_PEIM_UNUSED     0x000A
13. #define EFI_HOB_TYPE_UEFI_CAPSULE         0x000B
14. #define EFI_HOB_TYPE_FV3                  0x000C
15. #define EFI_HOB_TYPE_UNUSED               0xFFFE
16. #define EFI_HOB_TYPE_END_OF_HOB_LIST      0xFFFF

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在MdeModulePkg/Core/Dxe/DxeMain/DxeMain.c中有一段代码：

1. /**
2.   Main entry point to DXE Core.
4.   @param  HobStart               Pointer to the beginning of the HOB List from PEI.
6.   @return This function should never return.
8. **/
9. VOID
10. EFIAPI
11. DxeMain (
12.   IN  VOID  *HobStart // 由PEI阶段传递的HOB(Handoff Block)列表开始地址
13.   )
14. {
15.   EFI_STATUS                    Status;
16.   EFI_PHYSICAL_ADDRESS          MemoryBaseAddress;
17.   UINT64                        MemoryLength;
18.   PE_COFF_LOADER_IMAGE_CONTEXT  ImageContext;
19.   UINTN                         Index;
20.   EFI_HOB_GUID_TYPE             *GuidHob;
21.   EFI_VECTOR_HANDOFF_INFO       *VectorInfoList;
22.   EFI_VECTOR_HANDOFF_INFO       *VectorInfo;
23.   VOID                          *EntryPoint;
25.   //
26.   // Setup the default exception handlers
27.   //
28.   VectorInfoList = NULL;
29.   GuidHob        = GetNextGuidHob (&gEfiVectorHandoffInfoPpiGuid, HobStart);
30. //
31. }

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此处的gEfiVectorHandoffInfoPpiGuid位置：MdePkg/MdePkg.dec

1. [Ppis]
2.   ## Include/Ppi/VectorHandoffInfo.h
3.   gEfiVectorHandoffInfoPpiGuid       = { 0x3cd652b4, 0x6d33, 0x4dce, { 0x89, 0xdb, 0x83, 0xdf, 0x97, 0x66, 0xfc, 0xca }}

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由此可知，gEfiVectorHandoffInfoPpiGuid为PPI GUID，PPI接口头文件路径：Include/Ppi/VectorHandoffInfo.h
在MdePkg/Include/Ppi/VectorHandoffInfo.h举行访问该PPI GUID

1. extern EFI_GUID  gEfiVectorHandoffInfoPpiGuid;

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在其中检察该PPI接口：MdePkg/Include/Ppi/VectorHandoffInfo.h

1. ///
2. /// EFI_VECTOR_HANDOFF_INFO entries that describes the interrupt and/or
3. /// exception vectors in use in the PEI Phase.
4. ///
5. typedef struct {
6.   //
7.   // The interrupt or exception vector that is in use and must be preserved.
8.   //
9.   UINT32      VectorNumber;
10.   //
11.   // A bitmask that describes the attributes of the interrupt or exception vector.
12.   //
13.   UINT32      Attribute;
14.   //
15.   // The GUID identifies the party who created the entry. For the
16.   // EFI_VECTOR_HANDOFF_DO_NOT_HOOK case, this establishes the single owner.
17.   //
18.   EFI_GUID    Owner;
19. } EFI_VECTOR_HANDOFF_INFO;
21. ///
22. /// Provides a description of the interrupt and/or exception vectors that
23. /// were established in the SEC Phase and need to persist into PEI and DXE.
24. ///
25. typedef struct _EFI_PEI_VECTOR_HANDOFF_INFO_PPI {
26.   //
27.   // Pointer to an array of interrupt and /or exception vectors.
28.   //
29.   EFI_VECTOR_HANDOFF_INFO    *Info;
30. } EFI_PEI_VECTOR_HANDOFF_INFO_PPI;

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EFI_PEI_VECTOR_HANDOFF_INFO_PPI的作用为：将向量表信息从PEI阶段传递到DXE阶段，用于在差别固件阶段之间传递与中断向量干系的信息

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