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diff --git a/Lessons/Lesson_14/README.md b/Lessons/Lesson_14/README.md new file mode 100644 index 0000000..abf8f44 --- /dev/null +++ b/Lessons/Lesson_14/README.md @@ -0,0 +1,427 @@ +In this lesson we'll try to print all the runtime variables available in our system. + +To do it, we need to use `GetNextVariableName()` API function from EFI Runtime Services: +``` +GetNextVariableName() + +Summary: +Enumerates the current variable names. + +Prototype: +typedef +EFI_STATUS +GetNextVariableName ( + IN OUT UINTN *VariableNameSize, + IN OUT CHAR16 *VariableName, + IN OUT EFI_GUID *VendorGuid + ); + +Parameters: +VariableNameSize The size of the VariableName buffer. The size must be large + enough to fit input string supplied in VariableName buffer. +VariableName On input, supplies the last VariableName that was returned by + GetNextVariableName(). On output, returns the Nullterminated string + of the current variable. +VendorGuid On input, supplies the last VendorGuid that was returned by + GetNextVariableName(). On output, returns the VendorGuid + of the current variable. + +Description +GetNextVariableName() is called multiple times to retrieve the VariableName and VendorGuid of all +variables currently available in the system. On each call to GetNextVariableName() the previous +results are passed into the interface, and on output the interface returns the next variable name data. +When the entire variable list has been returned, the error EFI_NOT_FOUND is returned. + +Note that if EFI_BUFFER_TOO_SMALL is returned, the VariableName buffer was too small for the next +variable. When such an error occurs, the VariableNameSize is updated to reflect the size of buffer +needed. In all cases when calling GetNextVariableName() the VariableNameSize must not exceed the +actual buffer size that was allocated for VariableName. The VariableNameSize must not be smaller the size +of the variable name string passed to GetNextVariableName() on input in the VariableName buffer. + +To start the search, a Null-terminated string is passed in VariableName; that is, VariableName is a pointer +to a Null character. This is always done on the initial call to GetNextVariableName(). When +VariableName is a pointer to a Null character, VendorGuid is ignored. + + +Status Codes Returned: +EFI_SUCCESS The function completed successfully. +EFI_NOT_FOUND The next variable was not found. +EFI_BUFFER_TOO_SMALL The VariableNameSize is too small for the result. + VariableNameSize has been updated with the size needed to complete the request. +... +``` + + +Earlier we've included `#include <Library/UefiBootServicesTableLib.h>` in our file to get `gST`/`gBS` +To get shortcut for the EFI Runtime Services Table we need to add similar include: +``` +#include <Library/UefiRuntimeServicesTableLib.h> +``` +You can look at this file (https://github.com/tianocore/edk2/blob/master/MdePkg/Library/UefiRuntimeServicesTableLib/UefiRuntimeServicesTableLib.c), but it simply adds `extern EFI_RUNTIME_SERVICES *gRT;` which is filled as `gRT = SystemTable->RuntimeServices;` in a library constructor call https://github.com/tianocore/edk2/blob/master/MdePkg/Library/UefiRuntimeServicesTableLib/UefiRuntimeServicesTableLib.c + +As spec says to start a search we need to create a string with 1 character that equals Null (=0). +To create such a string we will use `AllocateZeroPool` function. +``` +UINTN VariableNameSize = sizeof (CHAR16); +CHAR16* VariableName = AllocateZeroPool(sizeof(CHAR16)); +``` + +`AllocateZeroPool` is not a UEFI spec function but simply is a helper from the edk2 MemoryAllocationLib (https://github.com/tianocore/edk2/blob/master/MdePkg/Library/PeiMemoryAllocationLib/MemoryAllocationLib.c): +``` +/ ** + Allocates and zeros a buffer of type EfiBootServicesData. + ... + @param AllocationSize The number of bytes to allocate and zero. + + @return A pointer to the allocated buffer or NULL if allocation fails. +**/ + +VOID * +EFIAPI +AllocateZeroPool ( + IN UINTN AllocationSize + ) +``` + +This string is obviously wouldn't be enough to store variable names, so we definitely would get `EFI_BUFFER_TOO_SMALL` at least on the first call. +In this case we need to reallocate our buffer. We could do it with the help of `ReallocatePool` function. + +`RealocatePool` is another helper function from the edk2 MemoryAllocationLib (https://github.com/tianocore/edk2/blob/master/MdePkg/Library/PeiMemoryAllocationLib/MemoryAllocationLib.c): +``` +/** + Reallocates a buffer of type EfiBootServicesData. + ... + @param OldSize The size, in bytes, of OldBuffer. + @param NewSize The size, in bytes, of the buffer to reallocate. + @param OldBuffer The buffer to copy to the allocated buffer. This is an optional + parameter that may be NULL. + @return A pointer to the allocated buffer or NULL if allocation fails. +**/ + +VOID * +EFIAPI +ReallocatePool ( + IN UINTN OldSize, + IN UINTN NewSize, + IN VOID *OldBuffer OPTIONAL + ) +``` + +Let's create `ListVariables` app and try to print first variable: +``` +#include <Library/UefiBootServicesTableLib.h> +#include <Library/UefiLib.h> + +#include <Library/MemoryAllocationLib.h> +#include <Library/UefiRuntimeServicesTableLib.h> + +INTN EFIAPI ShellAppMain(IN UINTN Argc, IN CHAR16 **Argv) +{ + EFI_GUID VendorGuid; + UINTN VariableNameSize = sizeof (CHAR16); + CHAR16* VariableName = AllocateZeroPool(sizeof(CHAR16)); + if (VariableName == NULL) { + Print(L"Error on AllocateZeroPool call\n"); + return EFI_OUT_OF_RESOURCES; + } + + UINTN VariableNameSizeOld = VariableNameSize; + EFI_STATUS Status = gRT->GetNextVariableName(&VariableNameSize, VariableName, &VendorGuid); + if (Status == EFI_BUFFER_TOO_SMALL) { + VariableName = ReallocatePool(VariableNameSizeOld, VariableNameSize, VariableName); + if (VariableName == NULL) { + return EFI_OUT_OF_RESOURCES; + } + Status = gRT->GetNextVariableName(&VariableNameSize, VariableName, &VendorGuid); + if (Status == EFI_SUCCESS) { + Print(L"%g: %s\n", VendorGuid, VariableName); + } else { + Print(L"Error on 'gRT->GetNextVariableName' call: %s\n", Status); + return Status; + } + } else { + Print(L"Error on 'gRT->GetNextVariableName' call: %s\n", Status); + return Status; + } + FreePool(VariableName); + return EFI_SUCCESS; +} +``` + +If we try to execute it under OVMF we would get: +``` +FS0:\> ListVariables.efi +8BE4DF61-93CA-11D2-AA0D-00E098032B8C: OsIndicationsSupported +``` + +Now we need to create a loop to print all the available variables. +``` +#include <Library/UefiBootServicesTableLib.h> +#include <Library/UefiLib.h> + +#include <Library/MemoryAllocationLib.h> +#include <Library/UefiRuntimeServicesTableLib.h> + +INTN EFIAPI ShellAppMain(IN UINTN Argc, IN CHAR16 **Argv) +{ + EFI_GUID VendorGuid; + UINTN VariableNameSize = sizeof (CHAR16); + CHAR16* VariableName = AllocateZeroPool(sizeof(CHAR16)); + if (VariableName == NULL) { + rint(L"Error on AllocateZeroPool call\n"); + return EFI_OUT_OF_RESOURCES; + } + + while (TRUE) + { + UINTN VariableNameSizeOld = VariableNameSize; + EFI_STATUS Status = gRT->GetNextVariableName(&VariableNameSize, VariableName, &VendorGuid); + if (Status == EFI_SUCCESS) { + Print(L"%g: %s\n", VendorGuid, VariableName); + } else if (Status == EFI_BUFFER_TOO_SMALL) { + VariableName = ReallocatePool(VariableNameSizeOld, VariableNameSize, VariableName); + if (VariableName == NULL) { + Print(L"Error on ReallocatePool call\n"); + return EFI_OUT_OF_RESOURCES; + } + Status = gRT->GetNextVariableName(&VariableNameSize, VariableName, &VendorGuid); + if (Status == EFI_SUCCESS) { + Print(L"%g: %s\n", VendorGuid, VariableName); + } else { + Print(L"Error on 'gRT->GetNextVariableName' call: %s\n", Status); + return Status; + } + } else if (Status == EFI_NOT_FOUND) { + FreePool(VariableName); + return EFI_SUCCESS; + } else { + Print(L"Error on 'gRT->GetNextVariableName' call: %s\n", Status); + return Status; + } + } + return EFI_SUCCESS; +} +``` + +Inside `while(TRUE)` loop we continiously run `gRT->GetNextVariableName` function and look for its returned `EFI_STATUS` code: +- `EFI_SUCCESS` means variable is successfully acquired, so we simply print it, +- `EFI_BUFFER_TOO_SMALL` means we need to grow our array with the `RealocatePool` API and call `gRT->GetNextVariableName` again, +- `EFI_NOT_FOUND` means we've parsed all variables and need to stop, +- on another status we simply return with error. + + +If we now run our program under OVMF we would get something like this: +``` +FS0:\> ListVariables.efi +8BE4DF61-93CA-11D2-AA0D-00E098032B8C: OsIndicationsSupported +8BE4DF61-93CA-11D2-AA0D-00E098032B8C: BootOptionSupport +8BE4DF61-93CA-11D2-AA0D-00E098032B8C: LangCodes +8BE4DF61-93CA-11D2-AA0D-00E098032B8C: PlatformLangCodes +8BE4DF61-93CA-11D2-AA0D-00E098032B8C: PlatformRecovery0000 +8BE4DF61-93CA-11D2-AA0D-00E098032B8C: ConOutDev +8BE4DF61-93CA-11D2-AA0D-00E098032B8C: ErrOutDev +8BE4DF61-93CA-11D2-AA0D-00E098032B8C: ConInDev +8BE4DF61-93CA-11D2-AA0D-00E098032B8C: BootCurrent +158DEF5A-F656-419C-B027-7A3192C079D2: path +158DEF5A-F656-419C-B027-7A3192C079D2: nonesting +0053D9D6-2659-4599-A26B-EF4536E631A9: cat +0053D9D6-2659-4599-A26B-EF4536E631A9: cd.. +0053D9D6-2659-4599-A26B-EF4536E631A9: cd\ +0053D9D6-2659-4599-A26B-EF4536E631A9: copy +0053D9D6-2659-4599-A26B-EF4536E631A9: del +0053D9D6-2659-4599-A26B-EF4536E631A9: dir +0053D9D6-2659-4599-A26B-EF4536E631A9: md +0053D9D6-2659-4599-A26B-EF4536E631A9: mem +0053D9D6-2659-4599-A26B-EF4536E631A9: mount +0053D9D6-2659-4599-A26B-EF4536E631A9: move +0053D9D6-2659-4599-A26B-EF4536E631A9: ren +158DEF5A-F656-419C-B027-7A3192C079D2: profiles +158DEF5A-F656-419C-B027-7A3192C079D2: uefishellsupport +158DEF5A-F656-419C-B027-7A3192C079D2: uefishellversion +158DEF5A-F656-419C-B027-7A3192C079D2: uefiversion +158DEF5A-F656-419C-B027-7A3192C079D2: cwd +158DEF5A-F656-419C-B027-7A3192C079D2: debuglasterror +158DEF5A-F656-419C-B027-7A3192C079D2: lasterror +59324945-EC44-4C0D-B1CD-9DB139DF070C: Attempt 1 +59324945-EC44-4C0D-B1CD-9DB139DF070C: Attempt 2 +59324945-EC44-4C0D-B1CD-9DB139DF070C: Attempt 3 +59324945-EC44-4C0D-B1CD-9DB139DF070C: Attempt 4 +59324945-EC44-4C0D-B1CD-9DB139DF070C: Attempt 5 +59324945-EC44-4C0D-B1CD-9DB139DF070C: Attempt 6 +59324945-EC44-4C0D-B1CD-9DB139DF070C: Attempt 7 +4B47D616-A8D6-4552-9D44-CCAD2E0F4CF9: InitialAttemptOrder +59324945-EC44-4C0D-B1CD-9DB139DF070C: Attempt 8 +8BE4DF61-93CA-11D2-AA0D-00E098032B8C: Boot0000 +8BE4DF61-93CA-11D2-AA0D-00E098032B8C: Timeout +8BE4DF61-93CA-11D2-AA0D-00E098032B8C: PlatformLang +8BE4DF61-93CA-11D2-AA0D-00E098032B8C: Lang +04B37FE8-F6AE-480B-BDD5-37D98C5E89AA: VarErrorFlag +8BE4DF61-93CA-11D2-AA0D-00E098032B8C: Key0000 +8BE4DF61-93CA-11D2-AA0D-00E098032B8C: Key0001 +8BE4DF61-93CA-11D2-AA0D-00E098032B8C: Boot0001 +8BE4DF61-93CA-11D2-AA0D-00E098032B8C: Boot0002 +8BE4DF61-93CA-11D2-AA0D-00E098032B8C: Boot0003 +4C19049F-4137-4DD3-9C10-8B97A83FFDFA: MemoryTypeInformation +5B446ED1-E30B-4FAA-871A-3654ECA36080: 525400123456 +8BE4DF61-93CA-11D2-AA0D-00E098032B8C: BootOrder +8BE4DF61-93CA-11D2-AA0D-00E098032B8C: Boot0004 +EB704011-1402-11D3-8E77-00A0C969723B: MTC +8BE4DF61-93CA-11D2-AA0D-00E098032B8C: ConOut +8BE4DF61-93CA-11D2-AA0D-00E098032B8C: ConIn +8BE4DF61-93CA-11D2-AA0D-00E098032B8C: ErrOut +``` + +The most important group is `8BE4DF61-93CA-11D2-AA0D-00E098032B8C`. It stands for `EFI_GLOBAL_VARIABLE` and is defined in UEFI spec. In edk2 you can find it under https://github.com/tianocore/edk2/blob/master/MdePkg/Include/Guid/GlobalVariable.h: +``` +#define EFI_GLOBAL_VARIABLE \ + { \ + 0x8BE4DF61, 0x93CA, 0x11d2, {0xAA, 0x0D, 0x00, 0xE0, 0x98, 0x03, 0x2B, 0x8C } \ + } + +extern EFI_GUID gEfiGlobalVariableGuid; +``` +Options such as `Boot####` are defined by UEFI specification, therefore they have this predefined GUID = `EFI_GLOBAL_VARIABLE`. If you'll ever want to have your own options, you shouldn't use `EFI_GLOBAL_VARIABLE` for them, but instead create your own to eliminate a possibility of variable name conflicts. + + +To look where GUID is defined in a edk2 codebase you could use something like this: +``` +$ grep -i 4B37FE8 -r ./ --exclude-dir=Build +``` + +To sort variables by GUID you can simply save output of our program and perform `sort` on it in Linux shell: +``` +$ cat guids.txt | sort +``` + + +All the variables grouped by GUID with links to files with GUID definition: + +`8BE4DF61-93CA-11D2-AA0D-00E098032B8C` - `gEfiGlobalVariableGuid` + +https://github.com/tianocore/edk2/blob/master/MdePkg/Include/Guid/GlobalVariable.h + +https://github.com/tianocore/edk2/blob/master/MdePkg/MdePkg.dec +``` +Boot0000 +Boot0001 +Boot0002 +Boot0003 +Boot0004 +BootCurrent +BootOptionSupport +BootOrder +ConIn +ConInDev +ConOut +ConOutDev +ErrOut +ErrOutDev +Key0000 +Key0001 +Lang +LangCodes +OsIndicationsSupported +PlatformLang +PlatformLangCodes +PlatformRecovery0000 +Timeout +``` + +`04B37FE8-F6AE-480B-BDD5-37D98C5E89AA` - `gEdkiiVarErrorFlagGuid` + +https://github.com/tianocore/edk2/blob/master/MdeModulePkg/Include/Guid/VarErrorFlag.h + +https://github.com/tianocore/edk2/blob/master/MdeModulePkg/MdeModulePkg.dec +``` +VarErrorFlag +``` + +`4C19049F-4137-4DD3-9C10-8B97A83FFDFA` - `gEfiMemoryTypeInformationGuid` + +https://github.com/tianocore/edk2/blob/master/MdeModulePkg/Include/Guid/MemoryTypeInformation.h + +https://github.com/tianocore/edk2/blob/master/MdeModulePkg/MdeModulePkg.dec +``` +MemoryTypeInformation +``` + +`5B446ED1-E30B-4FAA-871A-3654ECA36080` - `gEfiIp4Config2ProtocolGuid` + +https://github.com/tianocore/edk2/blob/master/MdePkg/Include/Protocol/Ip4Config2.h + +https://github.com/tianocore/edk2/blob/master/MdePkg/MdePkg.dec +``` +525400123456 +``` + + +`EB704011-1402-11D3-8E77-00A0C969723B` - `gMtcVendorGuid` + +https://github.com/tianocore/edk2/blob/master/MdeModulePkg/Include/Guid/MtcVendor.h + +https://github.com/tianocore/edk2/blob/master/MdeModulePkg/MdeModulePkg.dec +``` +MTC +``` + +`59324945-EC44-4C0D-B1CD-9DB139DF070C` - `gEfiIScsiInitiatorNameProtocolGuid` + +https://github.com/tianocore/edk2/blob/master/MdePkg/Include/Protocol/IScsiInitiatorName.h + +https://github.com/tianocore/edk2/blob/master/MdePkg/MdePkg.dec +``` +Attempt 1 +Attempt 2 +Attempt 3 +Attempt 4 +Attempt 5 +Attempt 6 +Attempt 7 +Attempt 8 +``` + +`158DEF5A-F656-419C-B027-7A3192C079D2` - `gShellVariableGuid` + +https://github.com/tianocore/edk2/blob/master/ShellPkg/Include/Guid/ShellVariableGuid.h + +https://github.com/tianocore/edk2/blob/master/ShellPkg/ShellPkg.dec +``` +cwd +debuglasterror +lasterror +nonesting +path +profiles +uefishellsupport +uefishellversion +uefiversion +``` + +`4B47D616-A8D6-4552-9D44-CCAD2E0F4CF9` - `gIScsiConfigGuid` + +https://github.com/tianocore/edk2/blob/master/NetworkPkg/Include/Guid/IScsiConfigHii.h + +https://github.com/tianocore/edk2/blob/master/NetworkPkg/NetworkPkg.dec +``` +InitialAttemptOrder +``` + +`0053D9D6-2659-4599-A26B-EF4536E631A9` - `gShellAliasGuid` + +https://github.com/tianocore/edk2/blob/master/ShellPkg/Include/Guid/ShellAliasGuid.h + +https://github.com/tianocore/edk2/blob/master/ShellPkg/ShellPkg.dec +``` +cat +cd.. +cd\ +copy +del +dir +md +mem +mount +move +ren +``` + |