The USED_SIZE FV_EXT_TYPE is introduced by PI 1.6 spec.

The EFI_FIRMWARE_VOLUME_EXT_ENTRY_USED_SIZE_TYPE can be used to find
out how many EFI_FVB2_ERASE_POLARITY bytes are at the end of the FV.

When the FV gets shadowed into memory you only need to copy the used
bytes into memory and fill the rest of the memory buffer with the
erase value.

Cc: Liming Gao <liming.gao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Star Zeng <star.zeng@intel.com>
---
 MdeModulePkg/Core/Pei/FwVol/FwVol.c | 91 +++++++++++++++++++++++++++++++++++--
 1 file changed, 88 insertions(+), 3 deletions(-)

diff --git a/MdeModulePkg/Core/Pei/FwVol/FwVol.c b/MdeModulePkg/Core/Pei/FwVol/FwVol.c
index 3da90f95312d..d96d591a47dc 100644
--- a/MdeModulePkg/Core/Pei/FwVol/FwVol.c
+++ b/MdeModulePkg/Core/Pei/FwVol/FwVol.c
@@ -1295,6 +1295,69 @@ PeiFfsGetVolumeInfo (
 }
 
 /**
+  Find USED_SIZE FV_EXT_TYPE entry in FV extension header and get the FV used size.
+
+  @param[in]  FvHeader      Pointer to FV header.
+  @param[out] FvUsedSize    Pointer to FV used size returned,
+                            only valid if USED_SIZE FV_EXT_TYPE entry is found.
+  @param[out] EraseByte     Pointer to erase byte returned,
+                            only valid if USED_SIZE FV_EXT_TYPE entry is found.
+
+  @retval TRUE              USED_SIZE FV_EXT_TYPE entry is found,
+                            FV used size and erase byte are returned.
+  @retval FALSE             No USED_SIZE FV_EXT_TYPE entry found.
+
+**/
+BOOLEAN
+GetFvUsedSize (
+  IN EFI_FIRMWARE_VOLUME_HEADER     *FvHeader,
+  OUT UINT32                        *FvUsedSize,
+  OUT UINT8                         *EraseByte
+  )
+{
+  UINT16                                        ExtHeaderOffset;
+  EFI_FIRMWARE_VOLUME_EXT_HEADER                *ExtHeader;
+  EFI_FIRMWARE_VOLUME_EXT_ENTRY                 *ExtEntryList;
+  UINTN                                         ExtEntryListSize;
+  EFI_FIRMWARE_VOLUME_EXT_ENTRY_USED_SIZE_TYPE  *ExtEntryUsedSize;
+
+  ExtHeaderOffset = ReadUnaligned16 (&FvHeader->ExtHeaderOffset);
+  if (ExtHeaderOffset != 0) {
+    ExtHeader = (EFI_FIRMWARE_VOLUME_EXT_HEADER *) ((UINT8 *) FvHeader + ExtHeaderOffset);
+    ExtEntryList = (EFI_FIRMWARE_VOLUME_EXT_ENTRY *) (ExtHeader + 1);
+    ExtEntryListSize = ReadUnaligned32 (&ExtHeader->ExtHeaderSize) - sizeof (EFI_FIRMWARE_VOLUME_EXT_HEADER);
+    while (ExtEntryListSize >= sizeof (EFI_FIRMWARE_VOLUME_EXT_ENTRY)) {
+      if (ReadUnaligned16 (&ExtEntryList->ExtEntryType) == EFI_FV_EXT_TYPE_USED_SIZE_TYPE) {
+        //
+        // USED_SIZE FV_EXT_TYPE entry is found.
+        //
+        ExtEntryUsedSize = (EFI_FIRMWARE_VOLUME_EXT_ENTRY_USED_SIZE_TYPE *) ExtEntryList;
+        *FvUsedSize = ReadUnaligned32 (&ExtEntryUsedSize->UsedSize);
+        if ((ReadUnaligned32 (&FvHeader->Attributes) & EFI_FVB2_ERASE_POLARITY) != 0) {
+          *EraseByte = 0xFF;
+        } else {
+          *EraseByte = 0;
+        }
+        DEBUG ((
+          DEBUG_INFO,
+          "FV at 0x%x has 0x%x used size, and erase byte is 0x%02x\n",
+          FvHeader,
+          *FvUsedSize,
+          *EraseByte
+          ));
+        return TRUE;
+      }
+      ExtEntryListSize -= ReadUnaligned16 (&ExtEntryList->ExtEntrySize);
+    }
+  }
+
+  //
+  // No USED_SIZE FV_EXT_TYPE entry found.
+  //
+  return FALSE;
+}
+
+/**
   Get Fv image from the FV type file, then install FV INFO(2) ppi, Build FV hob.
 
   @param PrivateData          PeiCore's private data structure
@@ -1326,7 +1389,9 @@ ProcessFvFile (
   EFI_FV_FILE_INFO              FileInfo;
   UINT64                        FvLength;
   UINT32                        AuthenticationStatus;
-  
+  UINT32                        FvUsedSize;
+  UINT8                         EraseByte;
+
   //
   // Check if this EFI_FV_FILETYPE_FIRMWARE_VOLUME_IMAGE file has already
   // been extracted.
@@ -1391,8 +1456,16 @@ ProcessFvFile (
       FvAlignment = 8;
     }
 
+    DEBUG ((
+      DEBUG_INFO,
+      "%a() FV at 0x%x, FvAlignment required is 0x%x\n",
+      __FUNCTION__,
+      FvHeader,
+      FvAlignment
+      ));
+
     //
-    // Check FvImage
+    // Check FvImage alignment.
     //
     if ((UINTN) FvHeader % FvAlignment != 0) {
       FvLength    = ReadUnaligned64 (&FvHeader->FvLength);
@@ -1400,7 +1473,19 @@ ProcessFvFile (
       if (NewFvBuffer == NULL) {
         return EFI_OUT_OF_RESOURCES;
       }
-      CopyMem (NewFvBuffer, FvHeader, (UINTN) FvLength);
+      if (GetFvUsedSize (FvHeader, &FvUsedSize, &EraseByte)) {
+        //
+        // Copy the used bytes and fill the rest with the erase value.
+        //
+        CopyMem (NewFvBuffer, FvHeader, (UINTN) FvUsedSize);
+        SetMem (
+          (UINT8 *) NewFvBuffer + FvUsedSize,
+          (UINTN) (FvLength - FvUsedSize),
+          EraseByte
+          );
+      } else {
+        CopyMem (NewFvBuffer, FvHeader, (UINTN) FvLength);
+      }
       FvHeader = (EFI_FIRMWARE_VOLUME_HEADER*) NewFvBuffer;
     }
   }
-- 
2.7.0.windows.1

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