HOW TO: Disassembling the HII Database (Part 4)

The HII Database is the portion of the UEFI Specification that manages the user-interface resources, like forms, fonts, images and strings. The tool we've been developing parses the contents of the database and displays it. Up to this point, we've broken down the data into the constituent package lists, and then broken down package lists into packages, and then started looking at how form packages are encoded.

Form Set 

Form packages are encoded as a series of variable-length data structures, called opcodes. The previous article shows how the opcodes are parsed, and then a function for when the opcode is first encountered, and then another function for when the opcode's scope is completed.

EFI_IFR_FORM_SET

The top level objects in a forms package are all form sets. The form set describes a collection of forms, variable stores and default stores, associated with a GUID, prompt text, help text, an image and an animation.

typedef struct _EFI_IFR_FORM_SET {
  EFI_IFR_OP_HEADER        Header;
  EFI_GUID                 Guid;
  EFI_STRING_ID            FormSetTitle;
  EFI_STRING_ID            Help;
  UINT8                    Flags;
//EFI_GUID                 ClassGuid[];
} EFI_IFR_FORM_SET;

The Header  the standard IFR opcode header. The Guid uniquely identifies the form set. The title of the form set (FormSetTitle) and there is also help text (Help). There can be up to three class GUIDs, which provide a way to classify the form sets. These GUIDs (along with Guid) can be used in the SendForm() function call to specify which types of form sets will appear in the user-interface.

UefiHiiParseFormFormSetOp()

The top level objects in a forms package are all form sets. Form sets are collections of forms associated with a GUID.

EFI_STATUS
UefiHiiParseFormFormSetOp (
  IN CONST EFI_IFR_OP_HEADER *Op,
  IN OUT UEFI_HII_FORM_PKG_STATE *S
  )
{
  UINT8 ClassGuidCount;
  EFI_GUID *ClassGuid;
  EFI_STATUS s;
  EFI_IFR_FORM_SET *FormSetOp;
  SYS_STRA Guid;
  UINT32 i;

  FormSetOp = (EFI_IFR_FORM_SET *) Op;

  if (!UefiHiiOpIsValid (Op, S)) {
    return EFI_INVALID_PARAMETER;
  }
  if (S->FormSetP != NULL) {
    SYSINFO ("FORM_SET: Cannot be inside a FORM_SET opcode.\n");
    return EFI_INVALID_PARAMETER;
  }

  ClassGuid = (EFI_GUID *)(FormSetOp + 1);
  ClassGuidCount = FormSetOp->Flags & 0x03; // isolate class GUID count.
  if (ClassGuidCount * sizeof (EFI_GUID) + sizeof (EFI_IFR_FORM_SET) >
      Op->Length) {
    ...
    return EFI_INVALID_PARAMETER;
  }

  ...dump out debug information...

  S->FormSetP = SysNew (UefiHiiFormSetP);
  if (S->FormSetP == NULL) {
    s = EFI_OUT_OF_RESOURCES;
    goto exit;
  }

  memcpy (&S->FormSetP->Id, &FormSetOp->Guid, sizeof (EFI_GUID));
  S->FormSetP->Title = FormSetOp->FormSetTitle;
  S->FormSetP->Help = FormSetOp->Help;
  S->FormSetP->ClassIdCount = ClassGuidCount;
  memcpy (S->FormSetP->ClassIds, ClassGuid, ClassGuidCount * sizeof (EFI_GUID));

  if (!SysListAddTail (&S->FormPkgP->FormSets, S->FormSetP)) {
    SysDelete (S->FormSetP);
    S->FormSetP = NULL;
    s = EFI_OUT_OF_RESOURCES;
    goto exit;
  }

  s = EFI_SUCCESS;
exit:
  SysEmpty (&Guid);
  return s;
}

This function checks to make sure that we aren't already inside of a form set scope. Also, since this opcode can be variable sized (with 0-3 class GUIDs), we also need to make sure that the opcode has a valid size. Then the function creates a new Form Set container and then populates the members with data from the IFR FORM_SET opcode. The Form Package parsing state is updated with the pointer to the Form Set container. Finally, the Form Set container is added to the list maintained as a part of the Form Package container.

UEFI_HII_FORM_SET_P

The UEFI_HII_FORM_SET_P object acts as the Form Set container.

typedef struct _UEFI_HII_FORM_SET_P {
  SYS_OBJ Obj;

  EFI_GUID Id;
  int ClassIdCount;                     // number of entries in ClassIds
  EFI_GUID ClassIds[3];
  EFI_STRING_ID Title;
  EFI_STRING_ID Help;
  EFI_IMAGE_ID Image;
  EFI_ANIMATION_ID Animation;

  SYS_LIST_O Forms;                     // list of Form containers.
  SYS_LIST_O VarStores;                 // list of Variable Store containers.
  SYS_LIST_O DefaultStores;             // list of Default Store containers.
  SYS_MAP_U16P Questions;               // question id <-> Statement container
} UEFI_HII_FORM_SET_P;

typedef UEFI_HII_FORM_SET_P UefiHiiFormSetP;

Most of these members map directly to the IFR FORM_SET opcode, like the GUID (Id), the class GUIDs (ClassIds and ClassIdCount), the title text (Title) and the help text (Help). In addition, as we process the opcodes inside the Form Set scope, we will update the attributes of the Form Set container.  For example, the IFR IMAGE opcode will update the Image member.

There are four types of objects where the identifier is only unique within a form set: forms, variable stores, default stores and questions. Thus, there are three object lists (forms, variable stores, default stores) and one map (for questions). The questions are handled separately because, although the identifier is unique within the form set, they are also a part of the forms.

UefiHiiParseFormFormSetEndOp()

Now, when we reach the end of the Form Set scope, the function UefiHiiParseFormFormSetEndOp() is called.

EFI_STATUS
UefiHiiParseFormFormSetEndOp (
  IN CONST EFI_IFR_OP_HEADER *Op,
  IN OUT UEFI_HII_FORM_PKG_STATE *S
  )
{
  S->FormSetP = NULL;
  return EFI_SUCCESS;
}

Pretty simple, huh? Just update the Form Package parsing state to NULL, indicating that there is no active form set.

Variable Stores

Variable stores describe a virtual buffer used for configuration setting storage for one or more questions. There are three types of variable stores: buffer, EFI variable and name/value. Each of them has an identifier, a name and a GUID.

EFI_IFR_VARSTORE, EFI_IFR_VARSTORE_EFI and EFI_IFR_VARSTORE_NAME_VALUE

There are actually three separate opcodes, one for each type of variable store.

typedef struct {
  EFI_IFR_OP_HEADER Header;
 
  EFI_GUID Guid;
  EFI_VARSTORE_ID VarStoreId;
  UINT16 Size;
//UINT8 Name[];
} EFI_IFR_VARSTORE;

For the buffer variable store, there is a variable store identifier (VarStoreId) associated with a GUID (Guid) and name (Name). In addition, buffer variable stores have to specify the size, in bytes (Size).

typedef struct _EFI_IFR_VARSTORE_NAME_VALUE {
  EFI_IFR_OP_HEADER Header;
  EFI_VARSTORE_ID VarStoreId;
  EFI_GUID Guid;
} EFI_IFR_VARSTORE_NAME_VALUE;

For the name/value variable store, there is a variable store identifier (VarStoreId) associated with a GUID (Guid). There is also a name, but that is provided by the question header rather than being embedded in the variable store opcode.

typedef struct _EFI_IFR_VARSTORE_EFI {
  EFI_IFR_OP_HEADER Header;

  EFI_VARSTORE_ID VarStoreId;
  EFI_GUID Guid;
  UINT32 Attributes
  UINT16 Size;
//UINT8 Name[];
} EFI_IFR_VARSTORE_EFI;

For the EFI variable store, there is a variable store identifier (VarStoreId) associated with a GUID (Guid) and name (Name). In addition, EFI variable stores have to specify the size, in bytes (Size) and the variable attributes (Attributes).

UefiHiiParseFormVarStoreOp()

The Variable Store container is used for all types of variable stores. For buffer variable stores, here is the function:

EFI_STATUS
UefiHiiParseFormVarStoreOp (
  IN EFI_IFR_OP_HEADER *Op,
  IN OUT UEFI_HII_FORM_PKG_STATE *S
  )
{
  EFI_STATUS s;
  EFI_IFR_VARSTORE *VarStoreOp;
  UEFI_HII_VAR_STORE_P *VarStoreP;
  SYS_LIST_POS pos;
  SYS_STRA Guid;
  UINT32 i;

  SysStrAInit (&Guid);
  VarStoreOp = (EFI_IFR_VARSTORE *) Op;

  if (!UefiHiiOpIsValid (Op, S) ||
      !UefiHiiOpInFormSet (Op, S) ||
      !UefiHiiOpNotInForm (Op, S)) {
    return EFI_INVALID_PARAMETER;
  }

  for (i = sizeof (EFI_IFR_VARSTORE); i < Op->Length; i++) {
    if (((UINT8 *)Op)[i] == 0x00) {
      break;
    }
  }
  if (i == Op->Length) {
    return EFI_INVALID_PARAMETER;
  }
  if (VarStoreOp->Size == 0) {
    return EFI_INVALID_PARAMETER;
  }
  if (VarStoreOp->VarStoreId == 0) {
    return EFI_INVALID_PARAMETER;
  }

  ...dump out debug information...

  for (pos = NULL; SysListGetNext (&S->FormSetP->VarStores, &pos, &VarStoreP);) {
    if (!SysIsValid (VarStoreP)) {
      continue;
    }
    if (VarStoreP->Id == VarStoreOp->VarStoreId) {
      s = EFI_SUCCESS;
      goto exit;
    }
  }

  VarStoreP = SysNew (UefiHiiVarStoreP);
  if (VarStoreP == NULL) {
    s = EFI_OUT_OF_RESOURCES;
    goto exit;
  }

  VarStoreP->Type = Op->OpCode;
  VarStoreP->Id = VarStoreOp->VarStoreId;
  memcpy (&VarStoreP->Guid, &VarStoreOp->Guid, sizeof (EFI_GUID));
  VarStoreP->Size = VarStoreOp->Size;
  SysStrACopyAStr (&VarStoreP->Name, (char *)(VarStoreOp + 1));

  if (!SysListAddTail (&S->FormSetP->VarStores, VarStoreP)) {
    s = EFI_OUT_OF_RESOURCES;
    goto exit;
  }

  s = EFI_SUCCESS;
exit:
  SysStrAEmpty (&Guid);
  return s;
}

So this function checks to make sure that opcode is formatted correctly, including the size of the opcode. It also checks that there is only one variable store with the given variable store identifier in the form set. Then it creates the new Variable Store container from the IFR VARSTORE opcode and adds it to the current Form Set container.

UefiHiiParseFormVarStoreEfiOp()

Now let's look at the function for EFI variable stores.

EFI_STATUS
UefiHiiParseFormVarStoreEfiOp (
  IN EFI_IFR_OP_HEADER *Op,
  IN OUT UEFI_HII_FORM_PKG_STATE *S
  )
{
  EFI_STATUS s;
  EFI_IFR_VARSTORE_EFI *VarStoreOp;
  UEFI_HII_VAR_STORE_P *VarStoreP;
  SYS_LIST_POS pos;
  SYS_STRA Guid;
  UINT32 i;

  SysStrAInit (&Guid);
  VarStoreOp = (EFI_IFR_VARSTORE_EFI *) Op;

  if (!UefiHiiOpIsValid (Op, S) ||
      !UefiHiiOpInFormSet (Op, S)) {
    return EFI_INVALID_PARAMETER;
  }

  for (i = sizeof (EFI_IFR_VARSTORE_EFI); i < Op->Length; i++) {
    if (((UINT8 *)Op)[i] == 0x00) {
      break;
    }
  }
  if (i == Op->Length) {
    return EFI_INVALID_PARAMETER;
  }

  if (VarStoreOp->Size == 0) {
    return EFI_INVALID_PARAMETER;
  }
  if (VarStoreOp->VarStoreId == 0) {
    return EFI_INVALID_PARAMETER;
  }
  if (VarStoreOp->Attributes == 0) {
    return EFI_INVALID_PARAMETER;
  }

  ...dump debug information...

  for (pos = NULL; SysListGetNext (&S->FormSetP->VarStores, &pos, &VarStoreP);) {
    if (!SysIsValid (VarStoreP)) {
      continue;
    }
    if (VarStoreP->Id == VarStoreOp->VarStoreId) {
      s = EFI_SUCCESS;
      goto exit;
    }
  }

  VarStoreP = SysNew (UefiHiiVarStoreP);
  if (VarStoreP == NULL) {
    s = EFI_OUT_OF_RESOURCES;
    goto exit;
  }

  VarStoreP->Type = Op->OpCode;
  VarStoreP->Id = VarStoreOp->VarStoreId;
  memcpy (&VarStoreP->Guid, &VarStoreOp->Guid, sizeof (EFI_GUID));
  VarStoreP->Size = VarStoreOp->Size;
  VarStoreP->Attribs = VarStoreOp->Attributes;
  SysStrACopyAStr (&VarStoreP->Name, (char *)(VarStoreOp + 1));

  if (!SysListAddTail (&S->FormSetP->VarStores, VarStoreP)) {
    s = EFI_OUT_OF_RESOURCES;
    goto exit;
  }

  s = EFI_SUCCESS;
exit:
  SysStrAEmpty (&Guid);
  return s;
}

This is very similar to the buffer variable store, except that the type is set with the IFR VARSTORE_EFI opcode value.

UefiHiiParseFormVarStoreNameValueOp()

Now we try the same trick for name/value variable stores. Here is the function:

EFI_STATUS
UefiHiiParseFormVarStoreNameValueOp (
  IN EFI_IFR_OP_HEADER *Op,
  IN OUT UEFI_HII_FORM_PKG_STATE *S
  )
{
  EFI_STATUS s;
  EFI_IFR_VARSTORE_NAME_VALUE *VarStoreOp;
  UEFI_HII_VAR_STORE_P *VarStoreP;
  SYS_LIST_POS pos;
  SYS_STRA Guid;

  SysStrAInit (&Guid);
  VarStoreOp = (EFI_IFR_VARSTORE_NAME_VALUE *) Op;

  if (!UefiHiiOpIsValid (Op, S) ||
      !UefiHiiOpInFormSet (Op, S)) {
    return EFI_INVALID_PARAMETER;
  }

  if (VarStoreOp->VarStoreId == 0) {
    return EFI_INVALID_PARAMETER;
  }

  ...dump debug information...

  for (pos = NULL; SysListGetNext (&S->FormSetP->VarStores, &pos, &VarStoreP);) {
    if (!SysIsValid (VarStoreP)) {
      continue;
    }
    if (VarStoreP->Id == VarStoreOp->VarStoreId) {
      s = EFI_SUCCESS;
      goto exit;
    }
  }

  VarStoreP = SysNew (UefiHiiVarStoreP);
  if (VarStoreP == NULL) {
    s = EFI_OUT_OF_RESOURCES;
    goto exit;
  }

  VarStoreP->Type = Op->OpCode;
  VarStoreP->Id = VarStoreOp->VarStoreId;
  memcpy (&VarStoreP->Guid, &VarStoreOp->Guid, sizeof (EFI_GUID));

  if (!SysListAddTail (&S->FormSetP->VarStores, VarStoreP)) {
    s = EFI_OUT_OF_RESOURCES;
    goto exit;
  }

  s = EFI_SUCCESS;
exit:
  SysStrAEmpty (&Guid);
  return s;
}

Like the two previous functions, the opcode is checked for validity. Then a new Variable Store container is created from the IFR VARSTORE_NAME_VALUE opcode and added to the Form Set.

UEFI_HII_VAR_STORE_P

The Variable Store container structure (UEFI_HII_VAR_STORE_P) describes a variable store.

typedef struct _UEFI_HII_VAR_STORE_P {
  SYS_OBJ Obj;

  UINT8 Type;                     // VARSTORE, VARSTORE_EFI, VARSTORE_NAME_VALUE
  EFI_VARSTORE_ID Id;    
  EFI_GUID Guid;                  // variable store GUID
  SYS_STRA Name;
  UINT16 Size;                    // for VARSTORE
  UINT32 Attribs;                 // for VARSTORE_EFI
} UEFI_HII_VAR_STORE_P;

typedef UEFI_HII_VAR_STORE_P UefiHiiVarStoreP;

The Type describes the type of Variable Store: buffer (VARSTORE), EFI variable (VARSTORE_EFI) and name/value (VARSTORE_NAME_VALUE). The variable stores all have at least a variable store identifier (Id) and a GUID (Guid). The name (Name) and size (Size) is used for buffer and EFI variable stores. The attributes (Attribs) are only used for EFI variable stores.  

Conclusion

So far, we've looked at how to parse the form sets and the associated variable stores. Next time we'll look at forms and default stores. As you can see, each major IFR object type has its own container.