[PATCH v1 12/30] DynamicTablesPkg: AML stream interface

["Sami Mujawar" <sami.mujawar@arm.com>]

Dynamic AML involves parsing/packing of AML opcode and
data into AML byte streams. The AML stream interface
provides safe buffer management as well as supports
forward and reverse streams. It provides functions to
create, read, write, clone and compare AML streams.

Co-authored-by: Pierre Gondois <pierre.gondois@arm.com>
Signed-off-by: Sami Mujawar <sami.mujawar@arm.com>
---
 DynamicTablesPkg/Library/Common/AmlLib/Stream/AmlStream.c | 665 ++++++++++++++++++++
 DynamicTablesPkg/Library/Common/AmlLib/Stream/AmlStream.h | 451 +++++++++++++
 2 files changed, 1116 insertions(+)

diff --git a/DynamicTablesPkg/Library/Common/AmlLib/Stream/AmlStream.c b/DynamicTablesPkg/Library/Common/AmlLib/Stream/AmlStream.c
new file mode 100644
index 0000000000000000000000000000000000000000..419e796e50cbe29e62234916c6e39c2c625a2951
--- /dev/null
+++ b/DynamicTablesPkg/Library/Common/AmlLib/Stream/AmlStream.c
@@ -0,0 +1,665 @@
+/** @file
+  AML Stream.
+
+  Copyright (c) 2019 - 2020, Arm Limited. All rights reserved.<BR>
+
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+**/
+
+#include <Stream/AmlStream.h>
+
+/** Initialize a stream.
+
+  @param  [in, out] Stream          Pointer to the stream to initialize.
+  @param  [in]      Buffer          Buffer to initialize Stream with.
+                                    Point to the beginning of the Buffer.
+  @param  [in]      MaxBufferSize   Maximum size of Buffer.
+  @param  [in]      Direction       Direction Stream is progressing
+                                    (forward, backward).
+
+  @retval EFI_SUCCESS             The function completed successfully.
+  @retval EFI_INVALID_PARAMETER   Invalid parameter.
+**/
+EFI_STATUS
+EFIAPI
+AmlStreamInit (
+  IN  OUT AML_STREAM              * Stream,
+  IN      UINT8                   * Buffer,
+  IN      UINT32                    MaxBufferSize,
+  IN      EAML_STREAM_DIRECTION     Direction
+  )
+{
+  if ((Stream == NULL)                            ||
+      (Buffer == NULL)                            ||
+      (MaxBufferSize == 0)                        ||
+      ((Direction != EAmlStreamDirectionForward)  &&
+       (Direction != EAmlStreamDirectionBackward))) {
+    ASSERT (0);
+    return EFI_INVALID_PARAMETER;
+  }
+
+  Stream->Buffer = Buffer;
+  Stream->MaxBufferSize = MaxBufferSize;
+  Stream->Index = 0;
+  Stream->Direction = Direction;
+
+  return EFI_SUCCESS;
+}
+
+/** Clone a stream.
+
+  Cloning a stream means copying all the values of the input Stream
+  in the ClonedStream.
+
+  @param  [in]  Stream          Pointer to the stream to clone.
+  @param  [in]  ClonedStream    Pointer to the stream to initialize.
+
+  @retval EFI_SUCCESS             The function completed successfully.
+  @retval EFI_INVALID_PARAMETER   Invalid parameter.
+**/
+EFI_STATUS
+EFIAPI
+AmlStreamClone (
+  IN  CONST AML_STREAM    * Stream,
+  OUT        AML_STREAM   * ClonedStream
+  )
+{
+  if (!IS_STREAM (Stream)   ||
+      (ClonedStream == NULL)) {
+    ASSERT (0);
+    return EFI_INVALID_PARAMETER;
+  }
+
+  ClonedStream->Buffer = Stream->Buffer;
+  ClonedStream->MaxBufferSize = Stream->MaxBufferSize;
+  ClonedStream->Index = Stream->Index;
+  ClonedStream->Direction = Stream->Direction;
+
+  return EFI_SUCCESS;
+}
+
+/** Initialize a sub-stream from a stream.
+
+  A sub-stream is a stream initialized at the current position of the input
+  stream:
+    - the Buffer field points to the current position of the input stream;
+    - the Index field is set to 0;
+    - the MaxBufferSize field is set to the remaining size of the input stream;
+    - the direction is conserved;
+
+  E.g.: For a forward stream:
+                   +----------------+----------------+
+                   |ABCD.........XYZ|   Free Space   |
+                   +----------------+----------------+
+                   ^                ^                ^
+  Stream:        Buffer          CurrPos         EndOfBuff
+  Sub-stream:                Buffer/CurrPos      EndOfBuff
+
+  @param  [in]  Stream      Pointer to the stream from which a sub-stream is
+                            created.
+  @param  [in]  SubStream   Pointer to the stream to initialize.
+
+  @retval EFI_SUCCESS             The function completed successfully.
+  @retval EFI_INVALID_PARAMETER   Invalid parameter.
+**/
+EFI_STATUS
+EFIAPI
+AmlStreamInitSubStream (
+  IN  CONST AML_STREAM  * Stream,
+  OUT       AML_STREAM  * SubStream
+  )
+{
+  if (!IS_STREAM (Stream) ||
+      (SubStream == NULL)) {
+    ASSERT (0);
+    return EFI_INVALID_PARAMETER;
+  }
+
+  if (IS_STREAM_FORWARD (Stream)) {
+    SubStream->Buffer = AmlStreamGetCurrPos (Stream);
+  } else if (IS_STREAM_BACKWARD (Stream)) {
+    SubStream->Buffer = Stream->Buffer;
+  } else {
+    ASSERT (0);
+    return EFI_INVALID_PARAMETER;
+  }
+
+  SubStream->MaxBufferSize = AmlStreamGetFreeSpace (Stream);
+  SubStream->Index = 0;
+  SubStream->Direction = Stream->Direction;
+
+  return EFI_SUCCESS;
+}
+
+/** Get the buffer of a stream.
+
+  @param  [in]  Stream    Pointer to a stream.
+
+  @return The stream's Buffer.
+          NULL otherwise.
+**/
+UINT8 *
+EFIAPI
+AmlStreamGetBuffer (
+  IN  CONST AML_STREAM  * Stream
+  )
+{
+  if (!IS_STREAM (Stream)) {
+    ASSERT (0);
+    return NULL;
+  }
+  return Stream->Buffer;
+}
+
+/** Get the size of Stream's Buffer.
+
+  @param  [in]  Stream    Pointer to a stream.
+
+  @return The Size of Stream's Buffer.
+          Return 0 if Stream is invalid.
+**/
+UINT32
+EFIAPI
+AmlStreamGetMaxBufferSize (
+  IN  CONST AML_STREAM  * Stream
+  )
+{
+  if (!IS_STREAM (Stream)) {
+    ASSERT (0);
+    return 0;
+  }
+  return Stream->MaxBufferSize;
+}
+
+/** Reduce the maximal size of Stream's Buffer (MaxBufferSize field).
+
+  @param  [in]  Stream    Pointer to a stream.
+  @param  [in]  Diff      Value to subtract to the Stream's MaxBufferSize.
+                          0 < x < MaxBufferSize - Index.
+
+  @retval EFI_SUCCESS             The function completed successfully.
+  @retval EFI_INVALID_PARAMETER   Invalid parameter.
+**/
+EFI_STATUS
+EFIAPI
+AmlStreamReduceMaxBufferSize (
+  IN  AML_STREAM  * Stream,
+  IN  UINT32        Diff
+  )
+{
+  if (!IS_STREAM (Stream)       ||
+      (Diff == 0)               ||
+      ((Stream->MaxBufferSize - Diff) <= Stream->Index)) {
+    ASSERT (0);
+    return EFI_INVALID_PARAMETER;
+  }
+
+  Stream->MaxBufferSize -= Diff;
+  return EFI_SUCCESS;
+}
+
+/** Get Stream's Index.
+
+  Stream's Index is incremented when writing data, reading data,
+  or moving the position in the Stream.
+  It can be seen as an index:
+   - starting at the beginning of Stream's Buffer if the stream goes forward;
+   - starting at the end of Stream's Buffer if the stream goes backward.
+
+  @param  [in]  Stream    Pointer to a stream.
+
+  @return Stream's Index.
+          Return 0 if Stream is invalid.
+**/
+UINT32
+EFIAPI
+AmlStreamGetIndex (
+  IN  CONST AML_STREAM  * Stream
+  )
+{
+  if (!IS_STREAM (Stream)) {
+    ASSERT (0);
+    return 0;
+  }
+  return Stream->Index;
+}
+
+/** Get Stream's Direction.
+
+  @param  [in]  Stream    Pointer to a stream.
+
+  @return Stream's Direction.
+          Return EAmlStreamDirectionUnknown if Stream is invalid.
+**/
+EAML_STREAM_DIRECTION
+EFIAPI
+AmlStreamGetDirection (
+  IN  CONST AML_STREAM  * Stream
+  )
+{
+  if (!IS_STREAM (Stream)) {
+    ASSERT (0);
+    return EAmlStreamDirectionInvalid;
+  }
+  return Stream->Direction;
+}
+
+/** Return a pointer to the current position in the stream.
+
+  @param  [in]  Stream    Pointer to a stream.
+
+  @return The current position in the stream.
+          Return NULL if error.
+**/
+UINT8 *
+EFIAPI
+AmlStreamGetCurrPos (
+  IN  CONST AML_STREAM  * Stream
+  )
+{
+  if (!IS_STREAM (Stream)) {
+    ASSERT (0);
+    return NULL;
+  }
+
+  if (IS_STREAM_FORWARD (Stream)) {
+    return Stream->Buffer + Stream->Index;
+  } else if (IS_STREAM_BACKWARD (Stream)) {
+    return Stream->Buffer + (Stream->MaxBufferSize - 1) - Stream->Index;
+  } else {
+    ASSERT (0);
+    return NULL;
+  }
+}
+
+/** Get the space available in the stream.
+
+  @param  [in]  Stream    Pointer to a stream.
+
+  @return Remaining space available in the stream.
+          Zero in case of error or if the stream is at its end.
+**/
+UINT32
+EFIAPI
+AmlStreamGetFreeSpace (
+  IN  CONST AML_STREAM  * Stream
+  )
+{
+  if (!IS_STREAM (Stream)) {
+    ASSERT (0);
+    return 0;
+  }
+
+  if (Stream->Index > Stream->MaxBufferSize) {
+    ASSERT (0);
+    return 0;
+  }
+
+  return Stream->MaxBufferSize - Stream->Index;
+}
+
+/** Move Stream by Offset bytes.
+
+  The stream current position is moved according to the stream direction
+  (forward, backward).
+
+  @param  [in]  Stream  Pointer to a stream.
+                        The stream must not be at its end.
+  @param  [in]  Offset  Offset to move the stream of.
+
+  @retval EFI_SUCCESS             The function completed successfully.
+  @retval EFI_INVALID_PARAMETER   Invalid parameter.
+  @retval EFI_BUFFER_TOO_SMALL    No space left in the buffer.
+**/
+EFI_STATUS
+EFIAPI
+AmlStreamProgress (
+  IN  AML_STREAM  * Stream,
+  IN  UINT32        Offset
+  )
+{
+  if (!IS_STREAM (Stream)         ||
+      IS_END_OF_STREAM  (Stream)  ||
+      (Offset == 0)) {
+    ASSERT (0);
+    return EFI_INVALID_PARAMETER;
+  }
+
+  if (AmlStreamGetFreeSpace (Stream) < Offset) {
+    ASSERT (0);
+    return EFI_BUFFER_TOO_SMALL;
+  }
+
+  Stream->Index += Offset;
+
+  return EFI_SUCCESS;
+}
+
+/** Rewind Stream of Offset bytes.
+
+  The stream current position is rewound according to the stream direction
+  (forward, backward). A stream going forward will be rewound backward.
+
+  @param  [in]  Stream  Pointer to a stream.
+  @param  [in]  Offset  Offset to rewind the stream of.
+
+  @retval EFI_SUCCESS             The function completed successfully.
+  @retval EFI_INVALID_PARAMETER   Invalid parameter.
+  @retval EFI_BUFFER_TOO_SMALL    No space left in the buffer.
+**/
+EFI_STATUS
+EFIAPI
+AmlStreamRewind (
+  IN  AML_STREAM  * Stream,
+  IN  UINT32        Offset
+  )
+{
+  if (!IS_STREAM (Stream) ||
+      (Offset == 0)) {
+    ASSERT (0);
+    return EFI_INVALID_PARAMETER;
+  }
+
+  if (AmlStreamGetIndex (Stream) < Offset) {
+    ASSERT (0);
+    return EFI_BUFFER_TOO_SMALL;
+  }
+
+  Stream->Index -= Offset;
+
+  return EFI_SUCCESS;
+}
+
+/** Reset the Stream (move the current position to the initial position).
+
+  @param  [in]  Stream  Pointer to a stream.
+
+  @retval EFI_SUCCESS             The function completed successfully.
+  @retval EFI_INVALID_PARAMETER   Invalid parameter.
+**/
+EFI_STATUS
+EFIAPI
+AmlStreamReset (
+  IN  AML_STREAM  * Stream
+  )
+{
+  if (!IS_STREAM (Stream)) {
+    ASSERT (0);
+    return EFI_INVALID_PARAMETER;
+  }
+
+  Stream->Index = 0;
+
+  return EFI_SUCCESS;
+}
+
+/** Peek one byte at Stream's current position.
+
+  Stream's position is not moved when peeking.
+
+  @param  [in]  Stream    Pointer to a stream.
+                          The stream must not be at its end.
+  @param  [out] OutByte   Pointer holding the byte value of
+                          the stream current position.
+
+  @retval EFI_SUCCESS           The function completed successfully.
+  @retval EFI_INVALID_PARAMETER Invalid parameter.
+  @retval EFI_BUFFER_TOO_SMALL  No space left in the buffer.
+**/
+EFI_STATUS
+EFIAPI
+AmlStreamPeekByte (
+  IN  AML_STREAM  * Stream,
+  OUT UINT8       * OutByte
+  )
+{
+  UINT8   * CurPos;
+
+  if (!IS_STREAM (Stream)       ||
+      IS_END_OF_STREAM (Stream) ||
+      (OutByte == NULL)) {
+    ASSERT (0);
+    return EFI_INVALID_PARAMETER;
+  }
+
+  CurPos = AmlStreamGetCurrPos (Stream);
+  if (CurPos == NULL) {
+    ASSERT (0);
+    return EFI_INVALID_PARAMETER;
+  }
+
+  *OutByte = *CurPos;
+  return EFI_SUCCESS;
+}
+
+/** Read one byte at Stream's current position.
+
+  The stream current position is moved when reading.
+
+  @param  [in]  Stream    Pointer to a stream.
+                          The stream must not be at its end.
+  @param  [out] OutByte   Pointer holding the byte value of
+                          the stream current position.
+
+  @retval EFI_SUCCESS           The function completed successfully.
+  @retval EFI_INVALID_PARAMETER Invalid parameter.
+  @retval EFI_BUFFER_TOO_SMALL  No space left in the buffer.
+**/
+EFI_STATUS
+EFIAPI
+AmlStreamReadByte (
+  IN  AML_STREAM  * Stream,
+  OUT UINT8       * OutByte
+  )
+{
+  EFI_STATUS    Status;
+
+  if (!IS_STREAM (Stream)       ||
+      IS_END_OF_STREAM (Stream) ||
+      (OutByte == NULL)) {
+    ASSERT (0);
+    return EFI_INVALID_PARAMETER;
+  }
+
+  // Stream is checked in the function call.
+  Status = AmlStreamPeekByte (Stream, OutByte);
+  if (EFI_ERROR (Status)) {
+    ASSERT (0);
+    return Status;
+  }
+
+  Status = AmlStreamProgress (Stream, 1);
+  ASSERT_EFI_ERROR (Status);
+  return Status;
+}
+
+/** Write Size bytes in the stream.
+
+  If the stream goes backward (toward lower addresses), the bytes written
+  to the stream are not reverted.
+  In the example below, writing "Hello" to the stream will not revert
+  the string. The end of the stream buffer will contain "Hello world!".
+  Stream buffer:
+     +---------------+-----+-----+-----+-----+-----+-----+---- +------+
+     |         ..... | ' ' | 'w' | 'o' | 'r' | 'l' | 'd' | '!' | '\0' |
+     +---------------+-----+-----+-----+-----+-----+-----+---- +------+
+                        ^
+                 Current position.
+
+  @param  [in]  Stream  Pointer to a stream.
+                        The stream must not be at its end.
+  @param  [in]  Buffer  Pointer to the data to write.
+  @param  [in]  Size    Number of bytes to write.
+
+  @retval EFI_SUCCESS             The function completed successfully.
+  @retval EFI_INVALID_PARAMETER   Invalid parameter.
+  @retval EFI_BUFFER_TOO_SMALL    No space left in the buffer.
+**/
+EFI_STATUS
+EFIAPI
+AmlStreamWrite (
+  IN        AML_STREAM  * Stream,
+  IN  CONST UINT8       * Buffer,
+  IN        UINT32        Size
+  )
+{
+  UINT8   * CurrPos;
+
+  if (!IS_STREAM (Stream)       ||
+      IS_END_OF_STREAM (Stream) ||
+      (Buffer == NULL)          ||
+      (Size == 0)) {
+    ASSERT (0);
+    return EFI_INVALID_PARAMETER;
+  }
+
+  if (AmlStreamGetFreeSpace (Stream) < Size) {
+    ASSERT (0);
+    return EFI_BUFFER_TOO_SMALL;
+  }
+
+  CurrPos = AmlStreamGetCurrPos (Stream);
+
+  // If the Stream goes backward, prepare some space to copy the data.
+  if (IS_STREAM_BACKWARD (Stream)) {
+    CurrPos -= Size;
+  }
+
+  CopyMem (CurrPos, Buffer, Size);
+  Stream->Index += Size;
+
+  return EFI_SUCCESS;
+}
+
+/** Compare Size bytes between Stream1 and Stream2 from their
+    respective current position.
+
+  Stream1 and Stream2 must go in the same direction.
+  Stream1 and Stream2 are left unchanged.
+
+  @param  [in]  Stream1   First stream to compare.
+                          The stream must not be at its end.
+  @param  [in]  Stream2   Second stream to compare.
+                          The stream must not be at its end.
+  @param  [in]  Size      Number of bytes to compare.
+                          Must be lower than the minimum remaining space of
+                          Stream1 and Stream2.
+                          Must be non-zero.
+
+  @retval TRUE  If Stream1 and Stream2 have Size bytes equal,
+                from their respective current position.
+                The function completed successfully.
+  @retval FALSE Otherwise.
+**/
+BOOLEAN
+EFIAPI
+AmlStreamCmp (
+  IN  CONST AML_STREAM    * Stream1,
+  IN  CONST AML_STREAM    * Stream2,
+  IN        UINT32          Size
+  )
+{
+  UINT32          MinSize;
+  UINT8         * CurrPosStream1;
+  UINT8         * CurrPosStream2;
+
+  if (!IS_STREAM (Stream1)                        ||
+      IS_END_OF_STREAM (Stream1)                  ||
+      !IS_STREAM (Stream2)                        ||
+      IS_END_OF_STREAM (Stream2)                  ||
+      (Stream1->Direction != Stream2->Direction)  ||
+      (Size == 0)) {
+    ASSERT (0);
+    return FALSE;
+  }
+
+  // Check the Size is not longer than the remaining size of
+  // Stream1 and Stream2.
+  MinSize = MIN (
+              AmlStreamGetFreeSpace (Stream1),
+              AmlStreamGetFreeSpace (Stream2)
+              );
+  if (MinSize < Size) {
+    ASSERT (0);
+    return FALSE;
+  }
+
+  CurrPosStream1 = AmlStreamGetCurrPos (Stream1);
+  if (CurrPosStream1 == NULL) {
+    ASSERT (0);
+    return FALSE;
+  }
+  CurrPosStream2 = AmlStreamGetCurrPos (Stream2);
+  if (CurrPosStream2 == NULL) {
+    ASSERT (0);
+    return FALSE;
+  }
+
+  if (Stream1->Direction == EAmlStreamDirectionForward) {
+    return (0 == CompareMem (CurrPosStream1, CurrPosStream2, MinSize));
+  }
+
+  // The stream is already pointing on the last byte, thus the (-1).
+  //          +---------------------+
+  // BStream  | | | | | | | |M|E|T|0|
+  //          +---------------------+
+  //                               ^
+  //                             CurrPos
+  return (0 == CompareMem (
+                  CurrPosStream1 - (MinSize - 1),
+                  CurrPosStream2 - (MinSize - 1),
+                  MinSize
+                  ));
+}
+
+/** Copy Size bytes of the stream's data to DstBuffer.
+
+  For a backward stream, the bytes are copied starting from the
+  current stream position.
+
+  @param  [out] DstBuffer         Destination Buffer to copy the data to.
+  @param  [in]  MaxDstBufferSize  Maximum size of DstBuffer.
+                                  Must be non-zero.
+  @param  [in]  Stream            Pointer to the stream to copy the data from.
+  @param  [in]  Size              Number of bytes to copy from the stream
+                                  buffer.
+                                  Must be lower than MaxDstBufferSize.
+                                  Must be lower than Stream's MaxBufferSize.
+                                  Return success if zero.
+
+  @retval EFI_SUCCESS           The function completed successfully.
+  @retval EFI_INVALID_PARAMETER Invalid parameter.
+**/
+EFI_STATUS
+EFIAPI
+AmlStreamCpyS (
+  OUT CHAR8         * DstBuffer,
+  IN  UINT32          MaxDstBufferSize,
+  IN  AML_STREAM    * Stream,
+  IN  UINT32          Size
+  )
+{
+  CHAR8   * StreamBufferStart;
+
+  // Stream is checked in the function call.
+  if ((DstBuffer == NULL)       ||
+      (MaxDstBufferSize == 0)   ||
+      (Size > MaxDstBufferSize) ||
+      (Size > AmlStreamGetMaxBufferSize (Stream))) {
+    ASSERT (0);
+    return EFI_INVALID_PARAMETER;
+  }
+
+  if (Size == 0) {
+    return EFI_SUCCESS;
+  }
+
+  // Find the address at which the data is starting.
+  StreamBufferStart = (CHAR8*)(IS_STREAM_FORWARD (Stream) ?
+                                 Stream->Buffer :
+                                 AmlStreamGetCurrPos (Stream));
+
+  CopyMem (DstBuffer, StreamBufferStart, Size);
+
+  return EFI_SUCCESS;
+}
diff --git a/DynamicTablesPkg/Library/Common/AmlLib/Stream/AmlStream.h b/DynamicTablesPkg/Library/Common/AmlLib/Stream/AmlStream.h
new file mode 100644
index 0000000000000000000000000000000000000000..cd2da89b072bd38f5c191f9ef35753b445b3f83d
--- /dev/null
+++ b/DynamicTablesPkg/Library/Common/AmlLib/Stream/AmlStream.h
@@ -0,0 +1,451 @@
+/** @file
+  AML Stream.
+
+  Copyright (c) 2019 - 2020, Arm Limited. All rights reserved.<BR>
+
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+**/
+
+#ifndef AML_STREAM_H_
+#define AML_STREAM_H_
+
+#include <AmlInclude.h>
+
+/** Stream direction.
+
+  Enum to choose the direction the stream is progressing.
+*/
+typedef enum EAmlStreamDirection {
+  EAmlStreamDirectionInvalid,     ///< Invalid AML Stream direction.
+  EAmlStreamDirectionForward,     ///< Forward direction.
+                                  ///  The Stream goes toward higher addresses.
+  EAmlStreamDirectionBackward,    ///< Forward direction.
+                                  ///  The Stream goes toward lower addresses.
+  EAmlStreamDirectionMax,         ///< Max enum.
+} EAML_STREAM_DIRECTION;
+
+/** Stream.
+
+  This structure is used as a wrapper around a buffer. It allows to do common
+  buffer manipulations (read, write, etc.) while preventing buffer overflows.
+*/
+typedef struct AmlStream {
+  /// Pointer to a buffer.
+  UINT8                 * Buffer;
+
+  /// Size of Buffer.
+  UINT32                  MaxBufferSize;
+
+  /// Index in the Buffer.
+  /// The Index field allows to keep track of how many bytes have been
+  /// read/written in the Buffer, and to retrieve the current stream position.
+  /// 0 <= Index <= MaxBufferSize.
+  /// If Index == MaxBufferSize, no more action is allowed on the stream.
+  UINT32                  Index;
+
+  /// The direction the stream is progressing.
+  /// If the stream goes backward (toward lower addresses), the bytes written
+  /// to the stream are not reverted.
+  /// In the example below, writing "Hello" to the stream will not revert
+  /// the string. The end of the stream buffer will contain "Hello world!".
+  /// Similarly, moving the stream position will be done according to the
+  /// direction of the stream.
+  /// Stream buffer:
+  ///    +---------------+-----+-----+-----+-----+-----+-----+---- +------+
+  ///    |-------------- | ' ' | 'w' | 'o' | 'r' | 'l' | 'd' | '!' | '\0' |
+  ///    +---------------+-----+-----+-----+-----+-----+-----+---- +------+
+  ///                       ^
+  ///                Current position.
+  EAML_STREAM_DIRECTION   Direction;
+} AML_STREAM;
+
+/** Check whether a StreamPtr is a valid Stream.
+
+  @param  [in]  Stream   Pointer to a stream.
+
+  @retval TRUE  Stream is a pointer to a stream.
+  @retval FALSE Otherwise.
+*/
+#define IS_STREAM(Stream)  (                                                  \
+          (((AML_STREAM*)Stream) != NULL)                                 &&  \
+          (((AML_STREAM*)Stream)->Buffer != NULL))
+
+/** Check whether a Stream is at the end of its buffer.
+
+  @param  [in]  Stream   Pointer to a stream.
+
+  @retval TRUE  Stream is a pointer to a non-full stream.
+  @retval FALSE Otherwise.
+*/
+#define IS_END_OF_STREAM(Stream)  (                                           \
+          (((AML_STREAM*)Stream)->Index ==                                    \
+             ((AML_STREAM*)Stream)->MaxBufferSize))
+
+/** Check Stream goes forward.
+
+  @param  [in]  Stream    Pointer to a stream.
+
+  @retval TRUE  Stream goes forward.
+  @retval FALSE Otherwise.
+*/
+#define IS_STREAM_FORWARD(Stream)   (                                         \
+    ((AML_STREAM*)Stream)->Direction == EAmlStreamDirectionForward)
+
+/** Check Stream goes backward.
+
+  @param  [in]  Stream   Pointer to a stream.
+
+  @retval TRUE  Stream goes backward.
+  @retval FALSE Otherwise.
+*/
+#define IS_STREAM_BACKWARD(Stream)   (                                        \
+    ((AML_STREAM*)Stream)->Direction == EAmlStreamDirectionBackward)
+
+/** Initialize a stream.
+
+  @param  [in, out] Stream          Pointer to the stream to initialize.
+  @param  [in]      Buffer          Buffer to initialize Stream with.
+                                    Point to the beginning of the Buffer.
+  @param  [in]      MaxBufferSize   Maximum size of Buffer.
+  @param  [in]      Direction       Direction Stream is progressing
+                                    (forward, backward).
+
+  @retval EFI_SUCCESS             The function completed successfully.
+  @retval EFI_INVALID_PARAMETER   Invalid parameter.
+**/
+EFI_STATUS
+EFIAPI
+AmlStreamInit (
+  IN  OUT AML_STREAM              * Stream,
+  IN      UINT8                   * Buffer,
+  IN      UINT32                    MaxBufferSize,
+  IN      EAML_STREAM_DIRECTION     Direction
+  );
+
+/** Clone a stream.
+
+  Cloning a stream means copying all the values of the input Stream
+  in the ClonedStream.
+
+  @param  [in]  Stream          Pointer to the stream to clone.
+  @param  [in]  ClonedStream    Pointer to the stream to initialize.
+
+  @retval EFI_SUCCESS             The function completed successfully.
+  @retval EFI_INVALID_PARAMETER   Invalid parameter.
+**/
+EFI_STATUS
+EFIAPI
+AmlStreamClone (
+  IN  CONST AML_STREAM    * Stream,
+  OUT        AML_STREAM   * ClonedStream
+  );
+
+/** Initialize a sub-stream from a stream.
+
+  A sub-stream is a stream initialized at the current position of the input
+  stream:
+    - the Buffer field points to the current position of the input stream;
+    - the Index field is set to 0;
+    - the MaxBufferSize field is set to the remaining size of the input stream;
+    - the direction is conserved;
+
+  E.g.: For a forward stream:
+                   +----------------+----------------+
+                   |ABCD.........XYZ|   Free Space   |
+                   +----------------+----------------+
+                   ^                ^                ^
+  Stream:        Buffer          CurrPos         EndOfBuff
+  Sub-stream:                Buffer/CurrPos      EndOfBuff
+
+  @param  [in]  Stream      Pointer to the stream from which a sub-stream is
+                            created.
+  @param  [in]  SubStream   Pointer to the stream to initialize.
+
+  @retval EFI_SUCCESS             The function completed successfully.
+  @retval EFI_INVALID_PARAMETER   Invalid parameter.
+**/
+EFI_STATUS
+EFIAPI
+AmlStreamInitSubStream (
+  IN  CONST AML_STREAM  * Stream,
+  OUT       AML_STREAM  * SubStream
+  );
+
+/** Get the buffer of a stream.
+
+  @param  [in]  Stream    Pointer to a stream.
+
+  @return The stream's Buffer.
+          NULL otherwise.
+**/
+UINT8 *
+EFIAPI
+AmlStreamGetBuffer (
+  IN  CONST AML_STREAM  * Stream
+  );
+
+/** Get the size of Stream's Buffer.
+
+  @param  [in]  Stream    Pointer to a stream.
+
+  @return The Size of Stream's Buffer.
+          Return 0 if Stream is invalid.
+**/
+UINT32
+EFIAPI
+AmlStreamGetMaxBufferSize (
+  IN  CONST AML_STREAM  * Stream
+  );
+
+/** Reduce the maximal size of Stream's Buffer (MaxBufferSize field).
+
+  @param  [in]  Stream    Pointer to a stream.
+  @param  [in]  Diff      Value to subtract to the Stream's MaxBufferSize.
+                          0 < x < MaxBufferSize - Index.
+
+  @retval EFI_SUCCESS             The function completed successfully.
+  @retval EFI_INVALID_PARAMETER   Invalid parameter.
+**/
+EFI_STATUS
+EFIAPI
+AmlStreamReduceMaxBufferSize (
+  IN  AML_STREAM  * Stream,
+  IN  UINT32        Diff
+  );
+
+/** Get Stream's Index.
+
+  Stream's Index is incremented when writing data, reading data,
+  or moving the position in the Stream.
+  It can be seen as an index:
+   - starting at the beginning of Stream's Buffer if the stream goes forward;
+   - starting at the end of Stream's Buffer if the stream goes backward.
+
+  @param  [in]  Stream    Pointer to a stream.
+
+  @return Stream's Index.
+          Return 0 if Stream is invalid.
+**/
+UINT32
+EFIAPI
+AmlStreamGetIndex (
+  IN  CONST AML_STREAM  * Stream
+  );
+
+/** Get Stream's Direction.
+
+  @param  [in]  Stream    Pointer to a stream.
+
+  @return Stream's Direction.
+          Return EAmlStreamDirectionUnknown if Stream is invalid.
+**/
+EAML_STREAM_DIRECTION
+EFIAPI
+AmlStreamGetDirection (
+  IN  CONST AML_STREAM  * Stream
+  );
+
+/** Return a pointer to the current position in the stream.
+
+  @param  [in]  Stream    Pointer to a stream.
+
+  @return The current position in the stream.
+          Return NULL if error.
+**/
+UINT8 *
+EFIAPI
+AmlStreamGetCurrPos (
+  IN  CONST AML_STREAM  * Stream
+  );
+
+/** Get the space available in the stream.
+
+  @param  [in]  Stream    Pointer to a stream.
+
+  @return Remaining space available in the stream.
+          Zero in case of error or if the stream is at its end.
+**/
+UINT32
+EFIAPI
+AmlStreamGetFreeSpace (
+  IN  CONST AML_STREAM  * Stream
+  );
+
+/** Move Stream by Offset bytes.
+
+  The stream current position is moved according to the stream direction
+  (forward, backward).
+
+  @param  [in]  Stream  Pointer to a stream.
+                        The stream must not be at its end.
+  @param  [in]  Offset  Offset to move the stream of.
+
+  @retval EFI_SUCCESS             The function completed successfully.
+  @retval EFI_INVALID_PARAMETER   Invalid parameter.
+  @retval EFI_BUFFER_TOO_SMALL    No space left in the buffer.
+**/
+EFI_STATUS
+EFIAPI
+AmlStreamProgress (
+  IN  AML_STREAM  * Stream,
+  IN  UINT32        Offset
+  );
+
+/** Rewind Stream of Offset bytes.
+
+  The stream current position is rewound according to the stream direction
+  (forward, backward). A stream going forward will be rewound backward.
+
+  @param  [in]  Stream  Pointer to a stream.
+  @param  [in]  Offset  Offset to rewind the stream of.
+
+  @retval EFI_SUCCESS             The function completed successfully.
+  @retval EFI_INVALID_PARAMETER   Invalid parameter.
+  @retval EFI_BUFFER_TOO_SMALL    No space left in the buffer.
+**/
+EFI_STATUS
+EFIAPI
+AmlStreamRewind (
+  IN  AML_STREAM  * Stream,
+  IN  UINT32        Offset
+  );
+
+/** Reset the Stream (move the current position to the initial position).
+
+  @param  [in]  Stream  Pointer to a stream.
+
+  @retval EFI_SUCCESS             The function completed successfully.
+  @retval EFI_INVALID_PARAMETER   Invalid parameter.
+**/
+EFI_STATUS
+EFIAPI
+AmlStreamReset (
+  IN  AML_STREAM  * Stream
+  );
+
+/** Peek one byte at Stream's current position.
+
+  Stream's position is not moved when peeking.
+
+  @param  [in]  Stream    Pointer to a stream.
+                          The stream must not be at its end.
+  @param  [out] OutByte   Pointer holding the byte value of
+                          the stream current position.
+
+  @retval EFI_SUCCESS           The function completed successfully.
+  @retval EFI_INVALID_PARAMETER Invalid parameter.
+  @retval EFI_BUFFER_TOO_SMALL  No space left in the buffer.
+**/
+EFI_STATUS
+EFIAPI
+AmlStreamPeekByte (
+  IN  AML_STREAM  * Stream,
+  OUT UINT8       * OutByte
+  );
+
+/** Read one byte at Stream's current position.
+
+  The stream current position is moved when reading.
+
+  @param  [in]  Stream    Pointer to a stream.
+                          The stream must not be at its end.
+  @param  [out] OutByte   Pointer holding the byte value of
+                          the stream current position.
+
+  @retval EFI_SUCCESS           The function completed successfully.
+  @retval EFI_INVALID_PARAMETER Invalid parameter.
+  @retval EFI_BUFFER_TOO_SMALL  No space left in the buffer.
+**/
+EFI_STATUS
+EFIAPI
+AmlStreamReadByte (
+  IN  AML_STREAM  * Stream,
+  OUT UINT8       * OutByte
+  );
+
+/** Write Size bytes in the stream.
+
+  If the stream goes backward (toward lower addresses), the bytes written
+  to the stream are not reverted.
+  In the example below, writing "Hello" to the stream will not revert
+  the string. The end of the stream buffer will contain "Hello world!".
+  Stream buffer:
+     +---------------+-----+-----+-----+-----+-----+-----+---- +------+
+     |         ..... | ' ' | 'w' | 'o' | 'r' | 'l' | 'd' | '!' | '\0' |
+     +---------------+-----+-----+-----+-----+-----+-----+---- +------+
+                        ^
+                 Current position.
+
+  @param  [in]  Stream  Pointer to a stream.
+                        The stream must not be at its end.
+  @param  [in]  Buffer  Pointer to the data to write.
+  @param  [in]  Size    Number of bytes to write.
+
+  @retval EFI_SUCCESS             The function completed successfully.
+  @retval EFI_INVALID_PARAMETER   Invalid parameter.
+  @retval EFI_BUFFER_TOO_SMALL    No space left in the buffer.
+**/
+EFI_STATUS
+EFIAPI
+AmlStreamWrite (
+  IN        AML_STREAM  * Stream,
+  IN  CONST UINT8       * Buffer,
+  IN        UINT32        Size
+  );
+
+/** Compare Size bytes between Stream1 and Stream2 from their
+    respective current position.
+
+  Stream1 and Stream2 must go in the same direction.
+  Stream1 and Stream2 are left unchanged.
+
+  @param  [in]  Stream1   First stream to compare.
+                          The stream must not be at its end.
+  @param  [in]  Stream2   Second stream to compare.
+                          The stream must not be at its end.
+  @param  [in]  Size      Number of bytes to compare.
+                          Must be lower than the minimum remaining space of
+                          Stream1 and Stream2.
+                          Must be non-zero.
+
+  @retval TRUE  If Stream1 and Stream2 have Size bytes equal,
+                from their respective current position.
+                The function completed successfully.
+  @retval FALSE Otherwise.
+**/
+BOOLEAN
+EFIAPI
+AmlStreamCmp (
+  IN  CONST AML_STREAM    * Stream1,
+  IN  CONST AML_STREAM    * Stream2,
+  IN        UINT32          Size
+  );
+
+/** Copy Size bytes of the stream's data to DstBuffer.
+
+  For a backward stream, the bytes are copied starting from the
+  current stream position.
+
+  @param  [out] DstBuffer         Destination Buffer to copy the data to.
+  @param  [in]  MaxDstBufferSize  Maximum size of DstBuffer.
+                                  Must be non-zero.
+  @param  [in]  Stream            Pointer to the stream to copy the data from.
+  @param  [in]  Size              Number of bytes to copy from the stream
+                                  buffer.
+                                  Must be lower than MaxDstBufferSize.
+                                  Must be lower than Stream's MaxBufferSize.
+                                  Return success if zero.
+
+  @retval EFI_SUCCESS           The function completed successfully.
+  @retval EFI_INVALID_PARAMETER Invalid parameter.
+**/
+EFI_STATUS
+EFIAPI
+AmlStreamCpyS (
+  OUT CHAR8         * DstBuffer,
+  IN  UINT32          MaxDstBufferSize,
+  IN  AML_STREAM    * Stream,
+  IN  UINT32          Size
+  );
+
+#endif // AML_STREAM_H_
-- 
'Guid(CE165669-3EF3-493F-B85D-6190EE5B9759)'