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authorKonstantin Aladyshev <aladyshev22@gmail.com>2021-06-19 21:03:52 +0300
committerKonstantin Aladyshev <aladyshev22@gmail.com>2021-06-19 21:07:18 +0300
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Rename lesson numbers to XX notation
With XX notation lessons would be placed in a folder from first to last.
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-Let's print GUID for all the protocols that are exist in our `IMAGE_HANDLE`.
-
-First understand what `EFI_GUID` internally means in the edk2 codebase:
-
-https://github.com/tianocore/edk2/blob/master/MdePkg/Include/Uefi/UefiBaseType.h
-```
-///
-/// 128-bit buffer containing a unique identifier value.
-///
-typedef GUID EFI_GUID;
-```
-`GUID` structure is defined in https://github.com/tianocore/edk2/blob/master/MdePkg/Include/Base.h :
-```
-///
-/// 128 bit buffer containing a unique identifier value.
-/// Unless otherwise specified, aligned on a 64 bit boundary.
-///
-typedef struct {
- UINT32 Data1;
- UINT16 Data2;
- UINT16 Data3;
- UINT8 Data4[8];
-} GUID;
-```
-Fortunately we don't have to manually print all these fields by hand. `Print` function has a format option `%g` to print GUIDs, so we could simply print GUIDs with a code like this:
-```
-Print("GUID=%g\n", myGUID);
-```
-More information about `Print` formating options can be found at https://github.com/tianocore/edk2/blob/master/MdePkg/Include/Library/PrintLib.h
-
-
-We want to print `EFI_GUID` field from the `PROTOCOL_ENTRY` structure which are referred from the `PROTOCOL_INTERFACE` structures. So we need to define both of these structures in our file for the same reason we've defined `IHANDLE` earlier.
-
-```
-typedef struct {
- UINTN Signature;
- /// Link Entry inserted to mProtocolDatabase
- LIST_ENTRY AllEntries;
- /// ID of the protocol
- EFI_GUID ProtocolID;
- /// All protocol interfaces
- LIST_ENTRY Protocols;
- /// Registerd notification handlers
- LIST_ENTRY Notify;
-} PROTOCOL_ENTRY;
-
-typedef struct {
- UINTN Signature;
- /// Link on IHANDLE.Protocols
- LIST_ENTRY Link;
- /// Back pointer
- IHANDLE *Handle;
- /// Link on PROTOCOL_ENTRY.Protocols
- LIST_ENTRY ByProtocol;
- /// The protocol ID
- PROTOCOL_ENTRY *Protocol;
- /// The interface value
- VOID *Interface;
- /// OPEN_PROTOCOL_DATA list
- LIST_ENTRY OpenList;
- UINTN OpenListCount;
-
-} PROTOCOL_INTERFACE;
-```
-
-`PROTOCOL_INTERFACE` structures that are connected to any HANDLE are interlinked with each other with a help of a `LIST_ENTRY Link` field that connects them to a double linked list.
-
-As you may remember `LIST_ENTRY` is defined like this:
-```
-///
-/// LIST_ENTRY structure definition.
-///
-typedef struct _LIST_ENTRY LIST_ENTRY;
-
-///
-/// _LIST_ENTRY structure definition.
-///
-struct _LIST_ENTRY {
- LIST_ENTRY *ForwardLink;
- LIST_ENTRY *BackLink;
-};
-```
-Each of these fields inside these structure points to another `LIST_ENTRY` structure that is placed in another `PROTOCOL_INTERFACE`.
-
-So this connection looks like this:
-
-```
-typedef struct { typedef struct {
- UINTN Signature; UINTN Signature;
- struct LIST_ENTRY { |---------> struct LIST_ENTRY {
- LIST_ENTRY *ForwardLink; -----------------| LIST_ENTRY *ForwardLink;
- LIST_ENTRY *BackLink; LIST_ENTRY *BackLink;
- } Link; } Link;
- IHANDLE *Handle; IHANDLE *Handle;
- LIST_ENTRY ByProtocol; LIST_ENTRY ByProtocol;
- PROTOCOL_ENTRY *Protocol; PROTOCOL_ENTRY *Protocol;
- VOID *Interface; VOID *Interface;
- LIST_ENTRY OpenList; LIST_ENTRY OpenList;
- UINTN OpenListCount; UINTN OpenListCount;
-} PROTOCOL_INTERFACE; } PROTOCOL_INTERFACE;
-```
-
-But in reality we want a pointer not to `Link` field of another `PROTOCOL_INTERFACE` structure, we want a pointer to another `PROTCOL_INTERFACE` structure inself.
-
-Therefore one more thing that we would need is a couple of macros:
-```
-#define offsetof(a,b) ((INTN)(&(((a*)(0))->b)))
-
-#define container_of(ptr, type, member) ({ \
- const typeof( ((type *)0)->member ) *__mptr = (ptr); \
- (type *)( (char *)__mptr - offsetof(type,member) );})
-```
-These macros can be familiar to you if you've investigated linux kernel programming. This is where I got them from anyway.
-
-`contianer_of` macro helps to get a pointer to a structure if you have a pointer to one of its fields.
-
-If you want to understand how it works internally in C language I suggest you to look at the https://stackoverflow.com/questions/15832301/understanding-container-of-macro-in-the-linux-kernel
-
-With all of this information final code for our `UefiMain` function would look like this:
-```
-EFI_STATUS
-EFIAPI
-UefiMain (
- IN EFI_HANDLE ImageHandle,
- IN EFI_SYSTEM_TABLE *SystemTable
- )
-{
- IHANDLE* MyHandle = ImageHandle;
- Print(L"Signature: %c %c %c %c\n", (MyHandle->Signature >> 0) & 0xff,
- (MyHandle->Signature >> 8) & 0xff,
- (MyHandle->Signature >> 16) & 0xff,
- (MyHandle->Signature >> 24) & 0xff);
-
- Print(L"Back Protocol Interface Link: %p\n", MyHandle->Protocols.BackLink);
- Print(L"Forward Protocol Interface Link: %p\n", MyHandle->Protocols.ForwardLink);
-
- LIST_ENTRY *FirstLink = MyHandle->Protocols.ForwardLink;
- LIST_ENTRY *CurrentLink = FirstLink;
- do {
- PROTOCOL_INTERFACE* MyProtocolInterface = container_of(CurrentLink, PROTOCOL_INTERFACE, Link);
-
- Print(L"\n");
- Print(L"Current Link: %p\n", CurrentLink);
- Print(L"Signature: %c %c %c %c\n", (MyProtocolInterface->Signature >> 0) & 0xff,
- (MyProtocolInterface->Signature >> 8) & 0xff,
- (MyProtocolInterface->Signature >> 16) & 0xff,
- (MyProtocolInterface->Signature >> 24) & 0xff);
-
- Print(L"Back Link: %p\n", MyProtocolInterface->Link.BackLink);
- Print(L"Forward Link: %p\n", MyProtocolInterface->Link.ForwardLink);
- Print(L"GUID=%g\n", MyProtocolInterface->Protocol->ProtocolID);
- CurrentLink = MyProtocolInterface->Link.ForwardLink;
- } while (CurrentLink != FirstLink);
-
- return EFI_SUCCESS;
-}
-```
-
-If we compile and run our app in OVMF (I hope at this time I don't need to repeat how to do it):
-```
-FS0:\> ImageHandle.efi
-h n d l
-Back Protocol Interface Link: 68D4320
-Forward Protocol Interface Link: 6891520
-
-Current Link: 6891520
-p i f c
-Back Link: 6891430
-Forward Link: 6891B20
-GUID=752F3136-4E16-4FDC-A22A-E5F46812F4CA
-
-Current Link: 6891B20
-p i f c
-Back Link: 6891520
-Forward Link: 68D4320
-GUID=BC62157E-3E33-4FEC-9920-2D3B36D750DF
-
-Current Link: 68D4320
-p i f c
-Back Link: 6891B20
-Forward Link: 6891430
-GUID=5B1B31A1-9562-11D2-8E3F-00A0C969723B
-
-Current Link: 6891430
- ? ? ?
-Back Link: 68D4320
-Forward Link: 6891520
-GUID=00000000-0000-0000-0000-000000000000
-```
-
-Let's find first GUID by executing grep on the edk2 source:
-```
-$ grep -i 752F3136 -r ./ --exclude-dir=Build
-./MdePkg/Include/Protocol/ShellParameters.h: 0x752f3136, 0x4e16, 0x4fdc, { 0xa2, 0x2a, 0xe5, 0xf4, 0x68, 0x12, 0xf4, 0xca } \
-./MdePkg/MdePkg.dec: gEfiShellParametersProtocolGuid = { 0x752f3136, 0x4e16, 0x4fdc, {0xa2, 0x2a, 0xe5, 0xf4, 0x68, 0x12, 0xf4, 0xca }}
-```
-
-https://github.com/tianocore/edk2/blob/master/MdePkg/Include/Protocol/ShellParameters.h
-```
-#define EFI_SHELL_PARAMETERS_PROTOCOL_GUID \
- { \
- 0x752f3136, 0x4e16, 0x4fdc, { 0xa2, 0x2a, 0xe5, 0xf4, 0x68, 0x12, 0xf4, 0xca } \
- }
-```
-You can also see in in a https://github.com/tianocore/edk2/blob/master/MdePkg/MdePkg.dec file:
-```
- ## Include/Protocol/ShellParameters.h
- gEfiShellParametersProtocolGuid = { 0x752f3136, 0x4e16, 0x4fdc, {0xa2, 0x2a, 0xe5, 0xf4, 0x68, 0x12, 0xf4, 0xca }}
-```
-
-The next two GUIDs you can find in UEFI the specification.
-
-`EFI_LOADED_IMAGE_DEVICE_PATH_PROTOCOL` - When installed, the Loaded Image Device Path Protocol specifies the device path that was used when a PE/COFF image was loaded through the EFI Boot Service LoadImage().
-
-```
-#define EFI_LOADED_IMAGE_DEVICE_PATH_PROTOCOL_GUID \
-{0xbc62157e,0x3e33,0x4fec,\
- {0x99,0x20,0x2d,0x3b,0x36,0xd7,0x50,0xdf}}
-```
-
-`EFI_LOADED_IMAGE_PROTOCOL` - Can be used on any image handle to obtain information about the loaded image.
-```
-#define EFI_LOADED_IMAGE_PROTOCOL_GUID\
- {0x5B1B31A1,0x9562,0x11d2,\
- {0x8E,0x3F,0x00,0xA0,0xC9,0x69,0x72,0x3B}}
-```
-
-The last `PROTOCOL_INTERFACE` structure doesn't have a valid "p i f c" signature (in my case it is 0x20 0x0E 0xED 0x06), so we don't need to look at its GUID.
-